Hop, Walk or Bound? Limb Proportions in Kangaroos and the Probable Locomotion of the extinct genus Protemnodon

Hop, Walk or Bound? Limb Proportions in Kangaroos and the Probable Locomotion of the extinct genus Protemnodon | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Hop, Walk or Bound? Limb Proportions in Kangaroos and the Probable Locomotion of the extinct genus Protemnodon Billie Jones, Christine Marie Janis This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4006700/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 01 Jun, 2024 Read the published version in Journal of Mammalian Evolution → Version 1 posted 7 You are reading this latest preprint version Abstract Kangaroos (Macropodoidea) display a diversity of locomotor modes, from bounding quadrupedally to hopping bipedally, but hopping has a body mass limit, which was exceeded by a number of extinct taxa. In the Pleistocene a variety of "giant” kangaroos existed: members of the extinct subfamily Sthenurinae have been previously considered to have a type of locomotion different from extant kangaroos (bipedal striding), but the primary locomotor mode of the large species of the extinct "giant" genus Protemnodon , closely related to extant large kangaroos, has undergone little question. Here, the association between limb proportions and locomotor mode across Macropodoidea is assessed by examination of functional limb indices. We show that large (> 100 kg) Protemnodon species are unlike any other known macropodoids; their position in this functional morphospace, along with other evidence on humeral morphology, supports prior hypotheses of a primarily quadrupedal mode of locomotion, likely some sort of bounding. Macropodoidea Protemnodon Biomechanics Locomotion Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Introduction The conventional view of a kangaroo (superfamily Macropodoidea) is of a relatively large animal that locomotes via hopping (also referred to as bipedal saltation or ricochetal locomotion). Indeed, the “poster child” of kangaroos is the red or Eastern grey kangaroo ( Osphranter rufus and Macropus giganteus , respectively): however, members of Macropodoidea encompass a range of sizes and locomotor modes. Today, kangaroos (macropodoids, kangaroos in the broad sense) range from body masses of 500 g ( Hypsiprymnodon moschatus , the Musky Rat-Kangaroo) to > 70 kg ( O. rufus ) (Kear et al. 2008 ). With the exception of H. moschatus all extant kangaroos use hopping as a fast gait. For slow gaits kangaroos either employ a quadrupedal bound, or some mostly larger species (in the genera Macropus , Onychogalea , Osphranter , and Wallabia ) employ a “pentapedal walk” where the tail is used as a fifth limb in supporting the body (Dawson et al. 2015 ). Some species have abandoned hopping almost entirely to become primarily quadrupedal: for example, the tree kangaroos ( Dendrolagus spp.) hop intermittently when on the ground but usually bound or use a four-footed walk, the latter gait being used most often along tree branches (Windsor and Dagg 1971 ). Secondary reliance on quadrupedal locomotion has arisen multiple times within Macropodoidea. Potoroids (rat-kangaroos, Potoroidae) use their forelimbs to dig for food, and so can be termed “semi-fossorial”, and some potoroids (species of Potorous and Bettongia ) have been observed to climb (Seebeck and Rose 1989 ). Figure 1 shows a phylogeny of macropodoids including their mode of locomotion. Today the most efficient kangaroos in terms of energy consumption are the largest ( Osphranter rufus , Macropus giganteus and M. fuliginosus ); during hopping locomotion their oxygen consumption at speeds over 3.9 m/s does not increase with speed, a stark difference to the linear increase in oxygen consumption with speed for similar-sized quadrupedal mammals (Baudinette et al. 1992 ). Nevertheless, even the largest kangaroos, extant or extinct, are small in comparison with quadrupeds of similar ecology; i.e., ungulate placental mammals. Optimum body mass for hopping has in fact been found to be ~ 50 kg, the average body mass for today’s largest kangaroos (Bennett and Taylor 1995 ). As kangaroos increase in body mass they experience unusually high skeletal and tendon stresses (McGowan et al. 2008 ); this ultimately limits locomotor ability with a body mass limit to hopping predicted at 160 kg (Snelling et al. 2017 ). In the Pleistocene a variety of “giant” kangaroos existed that attained masses greatly above this optimum, reaching up to 230 kg (Helgen et al. 2006 ), and calling into question their ability to hop. Recent studies have found that the diversity of locomotor modes within Macropodoidea was likely far greater in the past than it is present day. The extinct sthenurines (Macropodidae: Sthenurinae) demonstrate anatomical evidence for a bipedal striding type locomotion (Janis et al. 2014 ), a notion supported by trackway data (Camens and Worthy 2019 ). Sthenurine forelimbs were likely not primarily weight-bearing at any gait (Wells and Tedford 1995 ; Janis et al. 2014 ; 2020 ; Jones et al. 2022 ), and their rigid lumbar region would also make spinal flexion for quadrupedal locomotion difficult (Wells and Tedford 1995 ). Wagstaffe et al. ( 2022 ) found that the resistance to bending stresses are different in the foot bones of similarly sized sthenurines and macropodines, supporting the hypothesis of different modes of locomotion in the two subfamilies. Several extinct macropodid taxa are hypothesized to have been at least semi-arboreal if not fully so. These include species in the Balbaridae (Oligo-Miocene stem macropodoids; Den Boer et al. 2019 ); Bohra , a Pleistocene stem dendrolagine but much larger than extant dendrolagines (tree-kangaroos); (Warburton and Prideaux 2010 ); and a derived Pleistocene macropodin, Congruus kitcheni , likely related to Protemnodon (see Fig. 1 ), around the size of an extant grey kangaroos (Warburton and Prideaux 2021 ). Of particular interest here is species in the genus Protemnodon , a close relative of the Macropus group of taxa in the Macropodini (i.e., Macropus , Osphranter and Notamacropus ) (Llamas et al. 2015 ). Although the genus originally was comprised of a miscellany of many different extinct and extant macropods, it is now limited to the smaller New Guinea species ( P. otibandus, P. snewini , ~ 50kg; Flannery 1994 , plus the related Nombe nombe ; Kerr and Prideaux 2022 ) and larger Australian species ( P. roechus 160 kg, P. anak ~ 131 kg, P. brehus ~ 110 kg; Helgen et al. 2006 ). The locomotor mode of this genus has remained somewhat a mystery, though in recent years more evidence has begun coming to light. The largest species of Protemnodon approached the body mass limit to hopping. With extremely short feet and long arms their body plan appears unsuited to hopping; nevertheless, it has long been assumed that the larger species of Protemnodon were consistent hoppers like their Macropus relatives, although the smaller New Guinea species that have short tibiae have been considered to have been quadrupedal (Kear et al. 2008 ). It has been suggested that the anatomy of the large species of Protemnodon may also reflect more reliance on quadrupedal locomotion (Den Boer 2018 ). Janis et al. ( 2020 ) and Jones et al. ( 2022 ) found that the proximal and distal humeral morphology of Protemnodon indicates a significantly greater proportion of the body weight was borne on the forelimbs than in extant hopping macropodids, supporting this hypothesis of quadrupedality. Here we present a study of relative limb proportions within Macropodoidea. Relative limb proportions and limb indices have been widely employed as a functional indicator of locomotor mode in extant and extinct mammals, although to date among large mammals only placentals have been considered (e.g., Van Valkenburgh 1987 ; Croft and Anderson 2008 ; Samuels and Van Valkenburgh 2008 ; Meachen-Samuels and Van Valkenburgh 2009 ; Meachen-Samuels 2012; Samuels et al. 2013 ; Shockey et al., 2007 ; Dunn 2018 ). The use of limb indices (i.e., proportions of one limb relative to another) has relative pros and cons over the use of individual linear measurements (see discussion in Dunn 2018 ): limb indices are considered to be a correlate of the mechanical advantage of the primary locomotor muscles (Samuels and Van Valkenburgh 2008 ). Limb indices also eliminate the effects of size, though not allometry (Chen and Wilson 2015 ). One disadvantage is that the data should be collected from a single individual, at least for any given index, which may be difficult given the fragmentary nature of fossils (see discussion below for data problems). If an extinct macropodid was employing a mode of locomotion divergent from extant taxa the relative proportions of its limbs will likely reflect this. Thus, the divergent types of locomotion proposed above for sthenurines and large species of Protemnodon are expected to be apparent in their limb proportions. This study will enable a better understanding of macropodoid biodiversity and ecomorphology, especially the locomotor diversity of Pleistocene forms. A potential locomotor mode for large species of Protemnodon is presented, given the evidence found here and in previous studies (Den Boer 2018 ; Janis et al. 2022; Jones et al. 2022 ). Material and Methods Investigation of macropodoid limb proportions Materials Linear measurements of macropodoid hindlimbs were taken from Janis et al. ( 2014 ) and forelimb plus some additional hindlimb data were collected in 2019 by Christine Janis from the South Australian Museum. Data consisted of 89 individuals spanning 52 species (Online Resource 1: Tables S1, S2), encompassing the entire macropodid locomotor and body mass range, comprising all known extant and most extinct genera. Each species was grouped into one of three locomotor modes from information from the literature: saltators (employ a significant amount of saltation, or hopping); sthenurines (included as their own group, assumed to be bipedal striders following Janis et al. 2014 : Procoptodon gilli , 54 kg. Procoptodon goliah , 232 kg, Simosthenurus occidentalis 118 kg, Sthenurus andersoni 72 kg. S. stirlingi 173 kg, S. tindalei , 127 kg; body masses from Helgen et al. 2006 ); and quadrupedal, comprising habitual quadrupeds (engaging in little to no saltation but capable of this gait, including tree-kangaroos) and obligate quadrupeds ( H. moschatus ). Extinct Macropus species ( M. titan ) were assumed to be saltators. Protemnodon species ( P. anak ~ 131 kg, P. brehus ~ 110 kg: body masses from Helgen et al. 2006 ) were included as unknowns. Methods The degree of completeness of the measurements varied between individuals. Several additional measurements were taken in ImageJ to the nearest 0.01 mm (Schneider et al. 2012 ), using high-resolution photographs taken by CMJ. All measurements were taken three times and an average calculated to ensure maximum accuracy. Sixteen linear measurements (Fig. 2 ) were combined into a set of thirteen osteological indices (Table 1 ). Some of the indices were adopted from previous studies (see previous list of authors), whereas others are novel to this study. The number of indices that could be calculated for each individual for extinct taxa varied greatly according to the measurements available. All indices were calculated from single individuals except for a couple of extinct taxa ( Procoptodon gilli and Protemnodon anak , see Online Resource 1, Table S1 ). Although caution is warranted when using indices, due to the inability to control the effects of the denominator on the numerator and an inability to control for allometric effects (Dunn 2018 ), previous studies using indices (see above list) have nevertheless produced strong ecomorphological interpretations. Variation in the denominator and numerator between species was checked in this study to ensure values for each taxon were comparable. Table 1 List of the 13 osteological indices used in this study. See Fig. 2 for the abbreviations for the names of the bones. Bolded indices indicate those featured in Fig. 3 Index (Abbreviation) Forelimb Calculation Functional significance Brachial Index (BI) (U1/H1) x 100 Relative length of the forearm. Longer distal limb segments increase stride length. Longer proximal limb segments increase power during grasping and pulling (e.g., Richards et al. 2015 ). Epicondyle index (EI) (H4 + H3/H1) x 100 A measure of the volume of the carpal and digital flexor muscles (e.g., Samuels et al. 2013 ). Indicates capacity to manipulate items with the hands. Humeral Robustness Index (HRI) (H2/H1) x 100 Measure of the ability of the humerus to resist bending stresses (e.g., Echeverría et al. 2014 ); thus, an indication of the degree of weight bearing on the forelimbs. Olecranon Process Index (OPI) (U2/U1) x 100 Relates to the mechanical advantage of the triceps brachii muscle; a measure of the power of extension of the forelimb (e.g., Dunn 2018 ). Radial Index (RI) (R1/R2) x 100 Measure of the propensity for forearm supination. Higher values mean a more oval-shaped radial head and a restricted humero-radial joint (e.g., Dunn 2018 ). Hindlimb Crural Index (CI) (T1/F1) x 100 Relative length of the tibia. A longer distal hindlimb increases effective stride length and allows for a longer gastrocnemius (Achilles) tendon, the main tendon in elastic energy storage in macropodids. As used in Chen and Wilson ( 2015 ). Intermediate Phalanx Index (IPI)* (Ph2-L/Ph2-W) x 100 A measure of the length of the intermediate phalanx, independent of the length of the whole foot. Metatarsal Index (MI)* (Mt4-1/Mt4-2) x 100 A measure of the relative length of the metatarsal, independent of the length of the hindlimb. Metatarsal-Femur Index (MFI) (Mt4-1/F1) x 100 Relative length of the metatarsals (assuming femur length does not vary greatly between locomotor modes). A traditional measure of cursoriality and locomotor performance (e.g., Garland and Janis 1993 ). Metatarsal-Hindlimb Index (MHI)* (Mt4-1/F1 + T1 + Mt4-1) x 100 A measure of the proportion of the hindlimb taken up by the metatarsal. Proximal Phalanx Index (PPI)* (Ph1-L/ Ph1-W) x 100 A measure of the length of the proximal phalanx, independent of the length of the whole foot. Forelimb-Hindlimb Intermembral Index (IM) (H1 + U1/F1 + T1 + Mt4-1) x 100 Relative length of the forelimb versus the hindlimb. A measure of quadrupedality: fore- and hindlimbs are similar in length in quadrupeds. Forelimbs are reduced in size in bipeds. Often used in the study of primates (e.g., Granatosky 2018 ). Ulna-Femur Index (UFI)* (U1/F1) x 100 A measure of the relative length of the ulna independent of overall forelimb length. Calculations made based on the linear measurements shown in Fig. 2 . *Indicates an index that is novel to this study. The thirteen indices were subjected to analyses to determine the degree to which each discriminated between the locomotor groups and the placement of the Protemnodon species relative to the defined groups. The performance of the best seven indices is shown in Fig. 3 , but all were used in creating the principal components analysis (Fig. 4 ). All statistical tests were carried out in IBM SPSS Statistics v.26 (IBM Corp 2019 ). Kolmogorov-Smirnov (for indices where sample size was more than 50; Smirnov 1939 ) and Shapiro-Wilks (for a sample size of less than 50; Shapiro and Wilk 1965 ) tests were carried out on the indices to test for normality. ANOVA and Kruskal-Wallis tests (Fisher 1934 ; Kruskal and Wallis 1952 ) were then applied depending on the normality of the index to test whether there were significant differences between the locomotor groups. Due to increased risk of type I error when running multiple tests simultaneously results were adjusted using the Bonferroni correction (Bonferroni 1935 ). The following analyses were undertaken in RStudio (RStudio Team 2015 ). To reduce dimensionality and visualize the data, allowing easy comparison of Protemnodon species to the groups of known locomotor mode, a principal component analysis (PCA) was undertaken using the PCA function in the package FactoMineR (Lê et al. 2008 ). The dataset was pruned to include only those taxa (22) for which all indices were available: for the PCA only Protemnodon anak was comprised of several individuals, all from the Museum Victoria (Melbourne) collections and from the same locality (Morwell, Victoria). Fortunately, this did not impact the dataset range of body mass, locomotor mode and taxonomic diversity. A phylogenetic correction analysis (see Online Resource 2) showed little significant effects of phylogeny. Museum abbreviations AMNH = American Museum of Natural History, New York, USA. NHMUK = Natural History Museum, London, UK. NMS = National Museum of Scotland, Edinburgh, UK. NMV = Museum Victoria, Melbourne, Australia. SAM = South Australian Museum, Adelaide, Australia. UMCZ = University Museum of Zoology, Cambridge, UK. Results The indices varied in their ability to distinguish between the locomotor groups. The functional significance of each index is explained in Table 1 . Some other indices (e.g., radial index, epicondyle index) showed very little differentiation among the groups and are not shown in Fig. 3 and Online Resource 1, Table S2 ; others showed clear distinctions. We present here the indices that show the clearest distinctions between taxa: other indices are shown and discussed in Jones 2020 . Limb Indices Saltators and sthenurines have consistent values of Metatarsal-Femur Index (MFI – relative length of the metatarsal to the femur, Fig. 3 a) above 40. The largest extant kangaroos achieve values of around 60–76 (e.g., Osphranter rufus , #12, MFI: 75.8), reflecting a metatarsal more than two-thirds the length of the femur, but the extinct giant kangaroo, M. titan , #16, has a relatively low index (58.86) in comparison with other extant large species. Quadrupedal macropodids show lower values, with the lowest values occurring in the tree-kangaroos (e.g., Dendrolagus matschei , #73, 28.2). Protemnodon species (only the large ones P. anak and P. brehus are included here) have values most comparable to the quadrupeds ( P. anak , 36.38, #89, but P. brehus , #90, has a slightly higher value, 44.73). Quadrupedal taxa and Protemnodon species were significantly different (lower index) from both saltators and sthenurines (see Table S2 ). Patterns similar to MFI occur in other indices in Jones 2020 (Proximal Phalanx Index, Intermediate Phalanx Index, Metatarsal Index and Metatarsal-Hindlimb Index). Intermembral Index (IM – relative length of the forelimb to the hind limb, Fig. 3 b) was consistently below 51 for saltators, reflecting hindlimbs over double the length of the forelimbs. Similar values were seen in the sthenurines and in the terrestrial quadrupedal macropodids (potoroids, Setonix , Dorcopsis ), although these taxa tended to have somewhat higher values than most of the saltators. Conversely, the obligate quadrupedal bounder ( Hypsiprymnodon moschatus , #85, IM = 57.85) and the tree-kangaroos showed much higher values (e.g., De. goodfellowi , #69, IM = 69.90). The high values of the tree-kangaroos reflect adaptations to arboreality, with both relatively longer forelimbs and shorter hind limbs (Warburton & Prideaux 2021 ). The Protemnodon species have values most comparable to the obligate quadrupedal bounder H. moschatus . Crural Index (CI – relative length of the tibia to the femur, Fig, 3c) shows values over 120 in the saltators and the sthenurines, indicating a relatively long tibia. The largest extant kangaroos have a tibia more than twice the length of their femur (e.g., Macropus fuliginosus , #2, CI = 226.52), and have relatively longer tibiae than sthenurines (see Janis et al. 2023 ). Tree-kangaroos possess the lowest CI (e.g., De. dorianus , #68, CI = 97.8); their femur and tibia show little to no differentiation in length. Low values occur across the quadrupedal group (e.g., H. moschatus , #85, CI = 110.90; S. brachyurus , #78, CI = 115.3), with the exception of the dorcopsids (e.g., Dorcopsis muelleri , 98, CI = 141.70). Protemnodon species have relatively high values of CI (e.g., Pr. brehus , # 90, CI = 168.23). Quadrupedal taxa were statistically different (lower index) from saltators, sthenurines and Protemnodon species (see Online Resource 1, Table S3). Olecranon process index (OPI – relative length of the olecranon process to the shaft of the ulna, Fig. 3 d). Sthenurines have a notably low OPI (~ 10–13) and can be statistically distinguished from quadrupedal taxa and Protemnodon species (OPI ~ 18–21) (see Online Resource 1, Table S3). Most saltating macropodid taxa also have a low OPI (~ 10–17), but the semi-fossorial potoroids show much higher values (e.g., Aepyprymnus rufescens , #49, OPI = 26.00; Bettongia lesueur , #51, OPI = 20.44; Potorous longipes , #83, OPI = 23.02). Interestingly, the OPI of the Protemnodon species is relatively high, in particular Pr. brehus (#90, OPI = 21.18), with values comparable to those of B. lesueur and Po. longipes . Humeral robustness index (HRI – relative midshaft diameter of the humerus relative to its articular length, Fig. 3 e) shows the highest values (HRI ~ 10–13) in tree-kangaroos (#s 69, OPI = 10.65 and 72, OPI = 11.21) and in both semi-fossorial (e.g., B. lesueur , #51, OPI = 11.79) and quadrupedal (e.g., Do. luctuosa , #78, OPI = 13.13) taxa. However, some saltators ( Notamacropus eugenii , #11, OPI = 11.0; Onychogalea fraenata , #40, OPI = 12.88; Lagostrophus fasciatus , #46, OPI = 13.19) also have high values; the reason for this is not clear, and most saltators have values less than 10.5. Protemnodon species also exhibit some of the highest HRI values ( Pr. brehus , #90, OPI = 12.45, although the difference between Pr. brehus and Pr. anak (#s 86 and 87, OPIs = 10.15 and 10.47) may reflect different sexes and sexual dimorphism rather than functional differences. Ulna-Femur (UFI – relative length of the ulna to the femur; Fig. 3 F) and reflects elongation of the distal forelimb. The highest UFI values (> 70) are seen in the tree-kangaroos, the sthenurines and especially in the Protemnodon species. High values are also seen in the large macropodids, and in Notamacropus dorsalis (#19, a male specimen). The Protemnodon species are significantly different (higher) from the saltators (despite the high values of the large saltators), and the quadrupedal species (see Online Resource 1, Table S3). Brachial Index (BI – relative length of the ulna to the humerus; Fig. 3 g). This index also reflects elongation of the distal forelimb but relative to the proximal forelimb rather than to the femur. The lowest values of BI ( 135), reflecting a longer forearm relative to the humerus, are seen in the large saltators, Protemnodon species (especially Pr. anak , #s 86, 87, BI = 145.8) and, perhaps surprisingly, in the small (~ 50 kg, Helgen et al. 2006 ) sthenurine Procoptodon gilli (#56, BI = 171.13). Protemnodon species are statistically different from all other locomotor groups (higher index), and the sthenurines are statistically different from the saltators (lower index) (see Online Resource 1, Table S3). Principal Components Analysis The first three components of the PCA together explain 76.66% of the total variance. Figure 4 shows a plot of PC1 against PC2 (other PC axes were not significantly different with respect to the sorting of the taxa, see Online Resource 1, Table S4). The first component largely distinguishes the saltators and the sthenurines (positive scores) from the quadrupedal taxa and Protemnodon species (negative scores). This is because indices reflecting metatarsal length (e.g., Metarsal-Femur Index, MFI) have high positive values on this axis, whereas indices reflecting forelimb length (e.g., Intramembral Index, IM) have high negative values (see Online Resource 1, Table S4). The second component distinguishes Protemnodon species, the sthenurines and the large specialized saltators (i.e., Macropus and Osphranter ) (high Crural Index, CI, and Ulna-Femur Index, UFI; positive scores) from the quadrupeds and generalized (lower CI) and semi-fossorial saltators (high Olecranon Process Index, OPI; negative scores). Note: the extremely high score of O. rufus on PC1 is in part due to sexual dimorphism: this individual (NHMUK 205, #14 in Fig. 3 ) is a large male with an extremely high UFI (in contrast, the Macropus giganteus , NMV C5532, with lower scores on PC1, is a female). The sthenurines have similar scores to the large macropodines on PC1, but are separated from them on PC2, probably due to high UFIs. Although Protemnodon species possess a high UFI and relatively high CI, giving them high scores on PC1, their divergence from extant large macropodines along PC2 is related to their low MFI and high IM, plus relatively high Humeral Robustness Index. Discussion The results show that osteological indices are a good reflection of primary gait among macropodoids. Large Protemnodon species possess an unusual suit of osteological traits both similar to and different from quadrupedal and saltating extant macropodoids and also from the potentially bipedally-striding sthenurines. On the other hand, the sthenurines are similar to the large hopping macropodines in their hindlimb proportions, but differ in their forelimb proportions, likely due to their highly specialized hands reflecting a habit of using the forelimbs to procure food (Tedford 1966 ). Metatarsal length shows a strong relationship with primary locomotor mode, in particular when distinguishing between quadrupedal bounders vs. saltators (Kear et al. 2008 ). Metatarsal-Femur Index (MFI) is essentially a measure of stride length relative to the power of hindlimb extension (Polly 2020 ). Long metatarsals increase stride length (Hildebrand and Goslow 1982 ) and increase the lever arm for the action of the gastrocnemius tendon, allowing high speed, efficient hopping. More quadrupedal macropodines (e.g., Dorcopsis spp., Setonix ) have relatively short metatarsals in comparison to specialised hoppers like species of Macropus and Osphranter , as do tree-kangaroos ( Dendrolagus spp.). The short metatarsals of Protemnodon species, otherwise only seen in more quadrupedal extant kangaroos, must represent a secondary condition from the related Macropus complex extant macropodines, and are a strong indication they no longer relied on saltation as a dominant mode of locomotion. Figure 5 shows the feet of Protemnodon brehus in comparison with a specialized hopper ( M. giganteus ) and a tree-kangaroo ( D. inustus ), showing not only the short metatarsals of Protemnodon , but also the highly divergent fifth digit, more divergent than in the tree-kangaroo with similarly short metatarsals (although tree-kangaroos have relatively longer and more robust fifth digits). Sthenurines show fairly elongated metatarsals, but they are not as extremely elongated as those of the large specialized saltators. Intermembral Index (IM) measures the relative length of the fore- and hindlimbs. Relative lengthening of the hindlimbs in saltators is particularly striking because the forelimbs do not show similar modifications (Hildebrand and Goslow 1982 ); thus, saltators have low values of IM (Finch and Freedman 1988 ). A higher IM reflects less differentiation in the length of the fore- and hindlimbs, a necessary adaption if consistently walking quadrupedally and especially necessary when living an arboreal lifestyle; therefore, quadrupedal and arboreal macropodoids have high values of IM. With IM values close to that of quadrupedal bounding species ( Dendrolagus spp., H. moschatus ), the IMs of the large Protemnodon species suggest they engaged in consistently more quadrupedal locomotion than extant large kangaroos. Relatively low values of IM in sthenurines are likely a result of the adoption of fully bipedal locomotion, allowing the forelimbs to be specialized for food manipulation only (Janis et al. 2014 , 2020 ). Elongation of the distal limb is associated with adaptations for locomotor efficiency (Janis and Wilhelm 1993 ). Relative lengthening of the tibia (high Crural Index = CI) is part of the suit of morphological adaptations allowing efficient saltation in macropodoids (Hildebrand and Goslow 1982 ; Dawson et al. 2015 ), although it is a primarily a feature of the large macropodines (> 35 kg) where tibia length scales with positive allometry (Janis et al. 2023 ). Increasing the length of the tibia relative to the femur allows for a longer effective side length with little increase in the cost of limb recycling (Dawson and Webster 2010 ), and allows for long gastrocnemius tendons for storage of elastic energy. Note that, while both large Protemnodon species and sthenurines had long tibiae (sthenurines show a CI almost equivalent to the large hopping macropodines), these tibiae were still somewhat shorter than in the large extant macropodines (Janis et al. 2023 ). Although large Protemnodon species were likely too big and robust to be built for speed, retention of the long tibia from their macropodine ancestors indicates they may have benefited from the increased efficiency a longer distal hind limb provides with respect to maintaining an increased stride length (see discussion in Janis et al. 2023 ). Nevertheless, the long tibiae of large species of Protemnodon remain a puzzling feature, especially as the smaller New Guinea species had short tibiae (Kear et al. 2008 ), although the similarly sized Pliocene Australian species P. snewini did not (Bartholomai 1978 ). Extreme elongation of the tibia in large macropodines precludes their ability to employ a quadrupedal bound, necessitating adoption of the pentapedal walk at slow speeds (Dawson et al. 2015 ). Pentapedal locomotion is an extremely inefficient gait, more so than quadrupedal bounding (Bennett 2000 ). Positive correlation between body mass and time spent active for herbivores (Belovsky and Slade 1986 ) indicates a large animal such as Protemnodon would favour an efficient slow gait for foraging, but the large macropodines are restricted to using the inefficient pentapedal gait for this behaviour. The IM of large Protemnodon species is consistently greater than that of the pentapedal extant macropodines, indicating that they could have used a more efficient form of slow locomotion. A combination of long forelimbs and short feet may have allowed Protemnodon species to circumvent the constraints a high CI poses to extant macropodines, necessitating pentapedal walking (Dawson et al. 2015 ). Indeed, the relatively long distal transverse and mammillary processes the anterior caudal vertebrae (as seen in Pr. anak , NMV 39105) appear to indicate lack of weight-bearing tail use during locomotion (pers. obs. following Dawson 2015 ), although this requires further investigation. Nonetheless, it appears Protemnodon species were not entirely prioritising locomotor efficiency. The Olecranon Process Index (OPI) of Protemnodon species, in particular Pr. brehus , is remarkably similar to that of semi-fossorial potoroids. A longer olecranon process (high OPI) produces a greater mechanical advantage of the triceps brachii muscle (Dunn 2018 ), allowing the production of higher output forces from the forelimbs, a necessity for digging into the substrate. A shorter olecranon process allows full extension of the elbow, increasing forelimb length and stride length (Rodman 1979 ). Wells and Tedford ( 1995 ) note that the short olecranon processes of sthenurines (reflected here in their low OPI) would allow for arm extension during feeding. Large Protemnodon species appear to have been prioritizing forelimb power over stride length and this may be indicative that they engaged in digging (as proposed by Moore 2008 ). Furthermore, the robustness of a bone relates to its ability to resist the bending forces associated with either supporting the body weight or developing forces for specific limb functions, e.g., digging (Elissamburu and de Santis 2011 ). Digging behaviour is also reflected in the high Humeral Robustness Index (HRI) of large Protemnodon species, though this may be associated with increased quadrupedalism alone. It is interesting that the distal humeral morphology of large Protemnodon species is similar to that of the common wombat ( Vombatus ursinus ) (Jones et al. 2022 ). Figueirido et al. ( 2016 ) note the greater degree of forelimb stabilization in the wombat may relate to its semi-fossorial nature. Restriction of the forelimb to parasagittal movement is advantageous for digging as it prevents dislocation of the joint under pressure (Moore 2008 ). It is therefore entirely possible that the combination of features of a high degree of forelimb stabilization, large olecranon process and robust forelimbs of Protemnodon evince adaptations for digging. The short feet, with a divergent fifth digit (Fig. 5 ) and hooked phalanges (see below) would also have provided a stable base for this activity. Moore ( 2008 ) noted additional morphological similarities between Protemnodon species and the burrower Bettongia. lesueur (the boodie), and her discriminant function analysis of macropodoid forelimb anatomy found P. anak to plot between forage digging and shelter digging macropodoids. However, with no extant analogues it is difficult to distinguish between digging adaptations and simply the necessary adaptations for a large macropodid to bear weight consistently on its forelimbs. In contrast, sthenurines have some of the lowest OPIs of all macropodoids (see Fig. 3 ). A small olecranon process limits the ability of the arm to support the anterior body weight on the hands and use the arms for propulsion along the ground (Wells and Tedford 1995 ), supporting the notion that the sthenurines did not employ their forelimbs during locomotion. A final interesting feature of large Protemnodon species (the smaller ones have not been examined), which has not before been noted, is the strange nature of the intermediate pedal phalanges and the posture of the phalanges. The intermediate pedal phalanx is extremely short and broad, with a “puffy” appearance, very unlike any other macropodoid (see Fig. 6 ). The resistance to bending in the intermediate phalanx of Protemnodon brehus is different to other large macropodines, showing very little difference in resistance along the length of the bone; in contrast, other macropodines have a definite trough between proximal and distal peaks (Wagstaffe et al. 2022 ). A study of resistance to bending in small macropodids showed a similar resistance pattern in the tree-kangaroo Dendrolagus inustus , but not in any terrestrial taxon (Jones 2020 ). The phalanges of large Protemnodon species have a strange articulation (as observed by CMJ in at least a dozen different specimens, and see also Wagstaffe 2018 ). If placed flat on a surface they cannot be placed in articulation, unlike the condition in other kangaroos. Rather, the natural articulation appears for there to be a “hooking” between the intermediate and ungual phalanges (see Fig. 7 ). The function of this is not clear, but it likely allowed for a degree of gripping with the feet, enhanced by the long, curved ungual phalanges. The possible locomotor mode of Protemnodon While the superficial anatomy of large Protemnodon species is clearly that of a kangaroo, their detailed anatomy makes it a puzzling animal. This study has determined that the postcranial anatomy of Protemnodon is strongly divergent from that of large extant macropodines: large species of Protemnodon likely could not have employed sustained hopping locomotion like large extant kangaroos, although trackway data do indicate that they hopped at least occasionally (Belperio and Fotheringhamm 1990; Carey et al. 2011 ). Aspects of their forelimb anatomy indicate a much greater degree of weight-bearing on the forelimbs than large extant kangaroos, including the morphology of the proximal (Janis et al. 2020 ) and distal humerus (Jones et al. 2022 ). Large Protemnodon species plot in a vacant area of macropodoid morphospace (Fig. 4 ), indicating that there are no extant analogues. While the locomotor mode of large Protemnodon species will never be known for certain, much can be inferred based on the robust morphological observations presented here. Multiple lines of evidence indicate large Protemnodon species may have been predominantly quadrupedal. Den Boer ( 2018 ) noted the general curvature of their ungual phalanges (see Fig. 7 a, b): making comparisons to extant tree-kangaroos; she concluded this morphology may have provided grip and aided in maintaining balance on irregular substrates. The “hooking” of the pedal phalanges (Fig. 7 a, b) would also help with this. Given the size of large Protemnodon species and the forearm motion relatively restricted to the parasagittal plane (Janis et al. 2020 ; Jones et al. 2022 ), it is not suggested that they were engaging in arboreal activities (for which they would surely have been too large), but rather an enhancement of locomotion within a closed habitat. Isotopic values in the teeth of a species of Protemnodon at the Cuddie Springs site indicate a closed habitat ecology (DeSantis et al. 2017 ), and quadrupedal locomotion enables easier directional changes when navigating obstacles in dense forest habitats (Windsor and Dagg 1971 ). If large Protemnodon species inhabited woodland or forest, given their size adoption of quadrupedal locomotion may have been necessary to enable navigation of the dense forest floor, using their short, wide feet with divergent fifth digits and hooked toes to gain purchase on the irregular ground. As previously noted, the forearm morphology of large Protemnodon species is consistent with digging, and the short, broad feet may have aided in gaining purchase during such activities (see Hildebrand and Goslow 1982 ). A major question remains: were large Protemnodon species bounding using their hind legs synchronously (as in bounding kangaroos and other small bounding mammals) or asynchronously (i.e., some kind of galloping gait)? Asynchronous use of all four limbs is only seen today in the genus Dendrolagus (Windsor and Dagg 1971 ). The sacrum of Protemnodon is unusually large and broad (see Fig. 8 ). Janis et al. ( 2014 ) interpreted the large, broad sacrum of sthenurines as indicative of walking with alternate limbs, resisting rotational torsion at the sacroiliac joint. Although Protemnodon species never have more than two sacral vertebrae (as in other macropodids), while sthenurines sometimes have three (as shown here), the sacrum is proportionally much broader and more massive in general even than in sthenurines (see Fig. 8 ). Therefore, the large sacrum of Protemnodon could also be suggestive of the need to brace against the rotational forces associated with using the hindlimbs independently, perhaps indicating some sort of galloping quadrupedal gait (in contrast to bounding, which uses the hind limbs in synchrony). Jones et al. ( 2022 ) presented a restoration of Protemnodon anak based on the common way in which the genus is portrayed (from the mounted skeleton of Pr. anak in the South Australian Museum). Using new knowledge gained from this study an alternate restoration of Protemnodon anak is now proposed (Fig. 9 ). While the hypothesis that large species of Protemnodon may have had a quadrupedal, ‘semi-fossorial’ lifestyle is necessarily speculative, it is nonetheless grounded in the new understanding of its unique postcranial anatomy gained through this study. Conclusion The relative proportions of an macropodid limbs can be shown to be functionally relevant in determining its locomotor mode. Macropodid limb proportions differ significantly between the species specializing in the two different dominant modes of locomotion in extant macropodids: i.e., predominantly quadrupedal or predominantly saltatory. The morphology of the extinct sthenurines and large species of the extinct macropodine Protemnodon show them to be clearly distinguishable from extant species practicing these two dominant modes of locomotion. The results presented support prior hypotheses that macropodid locomotion was more diverse in the past and strengthen previous hypotheses that sthenurines employed bipedal striding and large species of Protemnodon were predominantly quadrupedal. A quadrupedal, closed habitat lifestyle is suggested for large species of Protemnodon in which they may have used their feet to grip the substrate. Additionally, multiple lines of evidence suggest these Protemnodon species may have engaged in digging behaviour. Declarations Competing Interests None Funding Funds from the University of Bristol Program in Palaeobiology enabled the scans. Funds to CMJ from the Bushnell Foundation (Brown University) aided in the collection of linear measurement data for the body mass estimations. Author Contribution BJ performed the original research from data largely provided from CJ. BJ and CJ wrote the main manuscript and prepared the initial figures (BJ Figs 1-4, 6, 9; CJ 5, 7-8). BJ and CJ reviewed the manuscript Acknowledgements We thank Jin Meng and Judy Galkin (Vertebrate Paleontology) at the American Museum of Natural History (New York, USA) for access to specimens in their care, and Ruth O’Leary and Ana Balcarel for facilitating the scans of Macropus giganteus and Sthenurus stirlingi (and thanks to all, plus Alana Gishlik, for the loan of the foot of Protemnodon brehus ). We thank other museum curators for access to specimens in their care for the measurements used: Jin Meng and Judy Galkin (Vertebrate Paleontology) and Eileen Westwig and Rob McPhee (Mammalogy) at the American Museum of Natural History (New York, USA); Rob Asher and Mathew Lowe at the University of Cambridge Museum of Zoology (Cambridge, UK); Roberto Portela Miguez at the Natural History Museum (London, UK); David Stemmer and Mary-Anne Binnie at the South Australian Museum, Adelaide, Australia. Helen Ryan and Kenny Travouillon at the Western Australian Museum (Perth, Australia); Adam Yates at the Museum and Art Gallery of the Northern Territory (Alice Springs, Australia); Tim Ziegler and Karen Roberts at the Museum Victoria, Melbourne, Australia); Sandy Ingleby and Anja Divaljan (Australian Museum, Sydney, Australia); Kirsten Spring and Scott Hocknull (Queensland Museum, Brisbane, AUS). For the scanning of the loaned specimens at the University of Bristol we thank Tom Davies and Liz Martin-Silverstone. For the figures, we thank Nuria Melisa Morales-García and Emily Green at Science Graphic Design. Data Availability All data generated or analyzed during this study are included in this published article and its supplementary information files References Bartholomai A (1978) The Macropodidae (Marsupialia) from the Allingham Formation, northern Queensland; results of the Ray E Lemley expedition, Part 2. Mem Queensl Mus 18:127–143 Baudinette R, Snyder GK, Frappell PB (1992) Energetic cost of locomotion in the tammar wallaby. Am J Physiol-Reg I 262:R771–R778 https://doi.org/10.1152/ajpregu.1992.262.5.R771 Belovsky GE, Slade J (1986) Time budgets of grassland herbivores: body size similarities. Oecol 70:53–62 https://doi.org/10.1007/BF00377110 Belperio AP, Fotheringham DG (1990) Geological setting of two quaternary footprint sites, western South Australia. Aust J Earth Sci 37:37–42 https://doi.org/10.1080/08120099008727903 Bennett M (2000) Unifying principles in terrestrial locomotion: do hopping Australian marsupials fit in? Physiol Biochem Zool 73:726–735 https://doi.org/10.1086/318110 Bennett MB, Taylor CR (1995) Scaling of elastic strain energy in kangaroos and the benefits of being big. Nature 378:56–59 Bonferroni CE (1935) Il calcolo delle assicurazioni su gruppi di teste. In: Carboni SO (ed) Onore del Professore Salvatore Ortu Carboni. Bardi, Rome, pp 13–60 Camens AB, Worthy TH (2019) Walk like a kangaroo: new fossil trackways reveal a bipedally striding macropodid in the Pliocene of Central Australia. J Vertebr Paleontol, Programs and Abstracts 2019:72 Carey SP, Camens AB, Cupper ML, Grun R, Hellstrom JC, McKnight SW, McLennan I, Pickering DA, Trusler M, Aubert M (2011) A diverse Pleistocene marsupial trackway assemblage from the Victorian Volcanic Plains. Australia Quaternary Sci Rev 30:591–610 https://doi.org/10.1016/j.quascirev.2010.11.021 Chen M, Wilson GP (2015) A multivariate approach to infer locomotor modes in Mesozoic mammals. Paleobiology 4:280–312 https://doi.org/10.1017/pab.2014.14 Croft DA, Anderson LC (2008) Locomotion in the extinct notoungulate Protypotherium . Palaeontol Electron, 1111A, 1–20 Dawson RS (2015) Morphological correlates of pentapedal locomotion in kangaroos and wallabies (Family: Macropodidae). Dissertation, The University of Western Australia, Perth Dawson RS, Warburton NM, Richards HL, Milne N (2015) Walking on five legs: investigating tail use during slow gait in kangaroos and wallabies. Aust J Zool 63:192–200 https://doi.org/10.1071/ZO15007 Dawson TJ, Webster K (2010) Energetic characteristics of macropodoid locomotion. In: Coulson G, Eldridge MDB (eds) Macropods: The Biology of Kangaroos, Wallabies, and Rat–kangaroos. CSIRO Publishing, Collingwood, Australia, pp 99–108 Den Boer W (2018) Evolutionary progression of the iconic Australasian kangaroos, rat-kangaroos, and their fossil relatives (Marsupiala: Macropodiformes). Dissertation, Uppsala University Den Boer W, Campione NE, Kear BP (2019) Climbing adaptations, locomotory disparity and ecological convergence in ancient stem ‘kangaroos’. R Soc Open Sci 6:181617 https://doi.org/10.1098/rsos.181617 DeSantis LRG, Field JH, Wroe S, Dodson JR (2017) Dietary responses of Sahul (Pleistocene Australia-New Guinea) megafauna to climate and environmental change. Paleobiology 43:181–185 https://doi.org/10.1017/pab.2016.50 Dunn RH (2018) Functional morphology of the postcranial skeleton. In: Croft DA, Su DF, Simpson SW (eds) Methods in Paleoecology: Reconstructing Cenozoic Terrestrial Environments and Ecological Communities. Springer International Publishing, Cham, pp 23–36 Echeverría AI, Becerra F, Vassallo AI (2014) Postnatal ontogeny of limb proportions and functional indices in the subterranean rodent Ctenomys talarum (Rodentia: Ctenomyidae). J Morphol 275:902–913 https://doi.org/10.1002/jmor.20267 Elissamburu A, de Santis L (2011) Forelimb proportions and fossorial adaptations in the scratch–digging rodent Ctenomys (Caviomorpha). J Mammal 92:683–689 https://doi.org/10.1644/09-MAMM-A-113.1 Figueirido B, Martín-Serra A, Janis CM (2016) Ecomorphological determinations in the absence of living analogues: the predatory behavior of the marsupial lion ( Thylacoleo carnifex ) as revealed by elbow joint morphology. Paleobiology 42:508–531 https://doi.org/10.1017/pab.2015.55 Finch M, Freedman L (1988) Functional-morphology of the limbs of Thylacoleo carnifex Owen (Thylacoleonidae, Marsupialia). Aust J Zool 36:251–272 https://doi.org/10.1071/ZO9880251 Fisher RA (1934) Statistical methods for research workers. In: Kots S, Johnson NL (eds) Breakthroughs in Statistics. Springer, New York, pp 66–70 Flannery TF (1994) The fossil land mammal record of New Guinea: a review. Sci New Guinea 20:39–48 Garland T Jr, Janis CM (1993) Does metatarsal/femur ratio predict maximal running speed in cursorial mammals? J Zool 229:133–151 https://doi.org/10.1111/j.1469-7998.1993.tb02626.x Granatosky MC (2018) A review of locomotor diversity in mammals with analyses exploring the influence of substrate use, body mass and intermembral index in primates. J Zool 306:207–216 https://doi.org/10.1111/jzo.12608 Helgen KM, Wells RT, Kear BP, Gerdtz WR, Flannery TF (2006) Ecological and evolutionary significance of sizes of giant extinct kangaroos. Aust J Zool 54:293–303 https://doi.org/10.1071/ZO05077 Hildebrand M, Goslow G (1982) Analysis of Vertebrate Structure. Wiley, NJ IBM Corp (2019) IBM SPSS Statistics for Macintosh, Version 260. Armonk, NY Janis CM, Wilhelm PB (1993) Were there mammalian pursuit predators in the Tertiary? Dances with wolf avatars. J Mamm Evol 1:103–125 https://doi.org/10.1007/BF01041590 Janis CM, Buttrill K, Figueirido B (2014) Locomotion in extinct giant kangaroos: were sthenurines hop-less monsters? PLoS One 9:e109888 https://doi.org/10.1371/journal.pone.0109888 Janis CM, Napoli JG, Billingham C, Martín-Serra A (2020) Proximal humerus morphology indicates divergent patterns of locomotion in extinct giant kangaroos. J Mammal Evol 27:627–647 https://doi.org/10.1007/s10914-019-09494-5 Janis CM, O’Driscoll AM, Kear BP (2023) Myth of the QANTAS leap: perspectives on the evolution of kangaroo locomotion. Alcheringa 47:671–685 https://doi.org/10.1080/03115518.2023.2195895 Jones B (2020) Locomotor divergence in Macropodoidea: Protemnodon was not a giant hopping kangaroo. Masters’ thesis, University of Bristol, Bristol Jones B, Martín-Serra A, Rayfield EJ, Janis CM (2022) Distal humeral morphology indicates locomotory divergence in extinct giant kangaroos. J Mammal Evol 29:27–41 https://doi.org/10.1007/s10914-021-09576-3 Kear BP, Lee MSY, Gerdtz WR, Flannery TF (2008) Evolution of hind limb proportions in kangaroos (Marsupalia: Macropodoidea). In: Sargis EF, Dagosto M (eds) Mammalian Evolutionary Morphology: A Tribute to Frederick S. Szalay. Springer, New York, pp 25–55 Kerr IA, Prideaux GJ (2022) A new genus of kangaroo (Marsupialia, Macropodidae) from the late Pleistocene of Papua New Guinea. T Roy Soc South Aust 146:295–318 https://doi.org/10.1080/03721426.2022.2086518 Kruskal WH, Wallis WA (1952) Use of ranks in one–criterion variance analysis. J Am Stat Assoc 47:583–621 https://doi.org/10.1080/01621459.1952.10483441 Llamas B, Brotherton P, Mitchell KJ, Templeton JEL, Thomson VA, Metcalf JL, Armstrong KN, Kasper M, Richards SM, Camens AB, Lee MSY, Cooper A (2015) Late Pleistocene Australian marsupial DNA clarifies the affinities of extinct megafaunal kangaroos and wallabies. Mol Biol Evol 32:574–584 https://doi.org/10.1093/molbev/msu338 Lê S, Josse J, Husson F (2008) FactoMineR: an R package for multivariate analysis. J Stat Softw 25:1–18 https://doi.org/10.18637/jss.v025.i01 McGowan CP, Skinner J, Biewener AA (2008) Hind limb scaling of kangaroos and wallabies (superfamily Macropodoidea): implications for hopping performance, safety factor, and elastic scaling. J Anat 212:153–163 https://doi.org/10.1111/j.1469-7580.2007.00841.x Meachen–Samuels J (2012) Morphological convergence of the prey–killing arsenal of sabretooth predators. Paleobiology 38:1–14 https://doi.org/10.1666/10036.1 Meachen-Samuels J, Van Valkenburgh B (2009) Forelimb indicators of prey-size preference in the Felidae. J Morphol 270:729–744 https://doi.org/10.1002/jmor.10712 Moore L (2008) Functional morphology and palaeoecology of extinct macropodoids, sthenurines and Protemnodon spp (Marsupialia; Diprotodontia) BSc thesis, Flinders University, South Australia Polly PD (2020) Ecometrics and Neogene faunal turnover: the roles of cats and hindlimb morphology in the assembly of carnivoran communities in the New World. Geodiversitas 42:257–304 https://doi.org/10.5252/geodiversitas2020v42a17 Richards H, Grueter C, Milne N (2015) Strong arm tactics: sexual dimorphism in macropodid limb proportions. J Zool 297:123–131 https://doi.org/10.1111/jzo.12264 Rodman PS (1979) Skeletal differentiation of Macaca fascicularis and Macaca nemestrina in relation to arboreal and terrestrial quadrupedalism. Am J Phys Anthropol 51:51–62 https://doi.org/10.1002/ajpa.1330510107 RSTUDIO Team (2015) RStudio: Integrated Development for R RStudio, Inc. Boston, MA. Available on: http://wwwrstudiocom/ Samuels JX, Van Valkenburgh B (2008) Skeletal indicators of locomotor adaptations in living and extinct rodents. J Morphol 269:1387–1411 https://doi.org/10.1002/jmor.10662 Samuels JX, Meachen JA, Sakai SA (2013) Postcranial morphology and the locomotor habits of living and extinct carnivorans. J Morphol 274:121–146 https://doi.org/10.1002/jmor.20077 Schneider CA, Rasband WS, Eliceiri KW (2012) NIH Image to ImageJ: 25 years of image analysis. Nat Methods 9:671–675 https://doi.org/10.1038/nmeth.2089 Seebeck JH, rose RW (1989) Potoroidae 1989. In: Walton DW, Richardson, BJ (eds) Fauna of Australia: Mammalia. Surrey Beatty, Sydney, pp. 716–739 Shapiro SS, Wilk MB (1965) An analysis of variance test for normality (complete samples). Biometrika 52:591–611 https://doi.org/10.2307/2333709 Shockey BJ, Croft DA, Anaya F (2007) Analysis of function in the absence of extant functional homologues: a case study using mesotheriid notoungulates (Mammalia). Paleobiology 33:227–247 https://doi.org/10.1666/05052.1 Smirnov NV (1939) Estimate of deviation between empirical distribution functions in two independent samples. Bull Mosc Univ 2:3–16 Snelling EP, Biewener AA, Hu Q, Taggart DA, Fuller A, Mitchell D, Maloney SK, Seymour RS (2017) Scaling of the ankle extensor muscle-tendon units and the biomechanical implications for bipedal hopping locomotion in the post-pouch kangaroo Macropus fuliginousus . J Anat 231:921–930 https://doi.org/10.1111/joa.12715 Tedford RH (1966) A review of the macropodid genus Sthenurus . Univ of Calif Publ in Geol Sci 64:1–165 Van Valkenburgh B (1987) Skeletal indicators of locomotor behavior in living and extinct carnivores. J Vertebr Paleontol 7:162–182 https://doi.org/10.1080/02724634.1987.10011651 Wagstaffe, AY (2018) The biomechanics of kangaroo feet: hopping for a better resolution. Masters’ thesis, University of Bristol, UK Wagstaffe AY, Kunz C, O'Driscoll AM, Janis CM, Rayfield EJ (2022) Divergent locomotion in “giant” kangaroos: Evidence from foot bone bending resistance and microanatomy. J Morphol 283:313–332 doi: 10.1002/jmor.21445 Warburton NM, Prideaux GJ (2010) Functional pedal morphology of the extinct tree-kangaroo Bohra (Diprotodontia: Macropodidae). In: Coulson G, Eldridge MDB (eds) Macropods: The Biology of Kangaroos, Wallabies, and Rat–kangaroos. CSIRO Publishing, Collingwood, Australia, pp 137–151 Warburton NM, Prideaux GJ (2021) The skeleton of Congruus kitcheneri , a semiarboreal kangaroo from the Pleistocene of southern Australia. R Soc Open Sci 8:202216. https://doi.org/10.1098/rsos.202216 Wells RT, Tedford RH (1995) Sthenurus (Macropodidae, Marsupialia) from the Pleistocene of Lake Callabonna, South Australia. Bull Am Mus Nat Hist 225:1–111 Westerman M, Loke S, Tan MH, Kear BP (2022) Mitogenome of the extinct Desert ‘rat-kangaroo’ times the adaptation to aridity in macropodoids. Sci Rep 12:5829 https://doi.org/10.1038/s41518-022-09568-0 Windsor D, Dagg A (1971) The gaits of the Macropodinae (Marsupialia). J Zool 163:165–175 https://doi.org/10.1111/j.1469-7998.1971.tb04530.x Additional Declarations No competing interests reported. Supplementary Files JonesandJanisOnlineResource1.doc Online Resource 1: Supplementary tables. JonesandJanisOnlineresource2.doc Online Resource 2: Phylogenetic analysis of principal components analysis Cite Share Download PDF Status: Published Journal Publication published 01 Jun, 2024 Read the published version in Journal of Mammalian Evolution → Version 1 posted Editorial decision: Revision requested 11 Apr, 2024 Reviews received at journal 22 Mar, 2024 Reviewers agreed at journal 15 Mar, 2024 Reviewers invited by journal 08 Mar, 2024 Editor assigned by journal 03 Mar, 2024 Submission checks completed at journal 03 Mar, 2024 First submitted to journal 02 Mar, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4006700","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":276552667,"identity":"a4221cb7-09ba-4bab-9977-18af67d07bc0","order_by":0,"name":"Billie Jones","email":"","orcid":"","institution":"University of Bristol","correspondingAuthor":false,"prefix":"","firstName":"Billie","middleName":"","lastName":"Jones","suffix":""},{"id":276552668,"identity":"ceaee3cb-1485-4b07-a1d9-fa9dcbc41eac","order_by":1,"name":"Christine Marie Janis","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABAklEQVRIie2PsUrEQBRFrwS0eZB2ZFj3F0YCKrj4LTMEJtVKwGarkA/QtY34E+lkK2cZ0MYPENZmexuxiSjoGFfWZhJLwTnFNO+ed98AgcBfhAGmfQEJCOyI1WCj7FTkWkl+pbThb1Tdp8SXZ8v5S3NwHAPL5zwvsitub3iO0aA2npKHW2FJspPtEimvhB3PplrzCjrxKYJpWPcX5QKSkzDj+o72FgSrupR545Rrg/SVRJGJL+W9UzH02QJo1xLJlWK8Crt3h5FmqjLQhyTs7ux0M3N1aXLhUeJKR0/NqFDnJaULeiuG+xTZhCZHg6lHWTN8lD8P7ou3bPVuDQQCgX/KBzB0WS2zlku/AAAAAElFTkSuQmCC","orcid":"","institution":"University of Bristol","correspondingAuthor":true,"prefix":"","firstName":"Christine","middleName":"Marie","lastName":"Janis","suffix":""}],"badges":[],"createdAt":"2024-03-02 14:15:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4006700/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4006700/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10914-024-09725-4","type":"published","date":"2024-06-01T05:17:33+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":52062606,"identity":"1b343342-d463-4211-ab3d-cf7082a16385","added_by":"auto","created_at":"2024-03-06 05:50:59","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":177097,"visible":true,"origin":"","legend":"\u003cp\u003eSimplified phylogeny of macropodoids\u003cstrong\u003e \u003c/strong\u003e(modified from Llamas et al. 2015, with the position of the Balbaridae from Den Boer et al. 2019, and the term Macropodia from Westerman et al. 2022).\u003cstrong\u003e \u003c/strong\u003eThe interrelationships of the “\u003cem\u003eMacropus\u003c/em\u003e complex” genera, \u003cem\u003eMacropus\u003c/em\u003e, \u003cem\u003eNotamacropus\u003c/em\u003eand \u003cem\u003eOsphranter\u003c/em\u003e, remain in debate.\u003cstrong\u003e \u003c/strong\u003eSee the text for explanations of the locomotor categories.\u003cstrong\u003e \u003c/strong\u003eDagger symbol (†) indicates an extinct taxon. Sources for silhouettes: \u003cem\u003eHypsiprymnodon moschatus, Bettongia lesueur, Setonix brachyurus\u003c/em\u003e and \u003cem\u003eTrichosurus vulpecula\u003c/em\u003e from \u003ca href=\"http://phylopic.org/\" target=\"_blank\"\u003ephylopic.org\u003c/a\u003e (Credits: Carly Monks [\u003cem\u003eB. lesueur\u003c/em\u003e], T. Michael Keesey [others], \u003cem\u003eS. brachyurus\u003c/em\u003e photo taken by Sean Mack, images available for reuse under the Attribution-ShareAlike 3.0 Unported license \u003ca href=\"https://creativecommons.org/licenses/by-sa/3.0/\" target=\"_blank\"\u003ehttps://creativecommons.org/licenses/by-sa/3.0/\u003c/a\u003e). All other silhouettes created by BJ using Inkscape, 2020. \u003cem\u003eOsphranter rufus\u003c/em\u003e created from a composite of images in the public domain; \u003cem\u003eSthenurus stirlingi\u003c/em\u003e modified from Regal in Janis et al. (2014), with permission from Brian Regal; \u003cem\u003eDendrolagus goodfellowi\u003c/em\u003e created from a photo taken by BJ of an animal in the Bristol Zoological Gardens; \u003cem\u003eProtemnodon anak\u003c/em\u003e created from a photo taken by CMJ of the mounted specimen in the South Australian Museum. Figure created in Adobe Illustrator by Science Graphic Design (sciencegraphicdesign.com)\u003c/p\u003e","description":"","filename":"JonesJanisFig1.png","url":"https://assets-eu.researchsquare.com/files/rs-4006700/v1/89eeb7948b7257d471b3314b.png"},{"id":52062601,"identity":"1633e9b0-5f77-4c81-bda1-ecf348a25d91","added_by":"auto","created_at":"2024-03-06 05:50:58","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":655547,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of the linear measurements obtained from the postcranial skeleton of 89 individual macropodoids spanning 52 extant and extinct species\u003cem\u003e. \u003c/em\u003eFigure created in Adobe Illustrator by Science Graphic Design (sciencegraphicdesign.com)\u003c/p\u003e","description":"","filename":"JonesJanisFig2.png","url":"https://assets-eu.researchsquare.com/files/rs-4006700/v1/03758f7d3b96f1096bb54a90.png"},{"id":52062599,"identity":"42a317f4-4cd9-4fa9-b490-d351a95a5d73","added_by":"auto","created_at":"2024-03-06 05:50:57","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":254126,"visible":true,"origin":"","legend":"\u003cp\u003eClustered column plots of the osteological indices calculated in this study. \u003cstrong\u003ea\u003c/strong\u003e. Metatarsal-Femur Index (MFI), dotted line denotes the minimum value achieved by saltators; \u003cstrong\u003eb\u003c/strong\u003e. Intermembral Index (IM), dotted line denotes the maximum value achieved by saltators; \u003cstrong\u003ec.\u003c/strong\u003e Crural Index (CI), dotted line denotes the minimum value achieved by saltators; \u003cstrong\u003ed.\u003c/strong\u003e Olecranon Process Index (OPI), dotted line denotes the value above which only extant semi-fossorial taxa (engage in digging for food) plot; \u003cstrong\u003ee.\u003c/strong\u003e Humeral Robustness Index (HR). F. Ulna-Femur Index (UFI); \u003cstrong\u003eg.\u003c/strong\u003e Brachial Index (BI). Locomotor type indicated by colors in the online version. A full list of taxa (and referring numbers) and indices can be found in Table S2\u003cem\u003e. \u003c/em\u003eFigure created in Adobe Illustrator by Science Graphic Design (sciencegraphicdesign.com)\u003c/p\u003e","description":"","filename":"JonesJanisFig3.png","url":"https://assets-eu.researchsquare.com/files/rs-4006700/v1/17973d3c7cfa68fbc877855b.png"},{"id":52062607,"identity":"48e1722a-e109-4d00-bf48-deedbd8d2f14","added_by":"auto","created_at":"2024-03-06 05:50:59","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":267944,"visible":true,"origin":"","legend":"\u003cp\u003ePrincipal Component Analysis (PCA) of the 13 osteological indices used in this study. Symbols differentiate the locomotor groups (plus colors in the online version). The variables factor map illustrates the loading of the indices in the morphospace. See Table S1 for taxon information. P. anak is a composite specimen constructed from all Protemnodon anak individuals in the dataset. All the rest are from single individuals. Sources for silhouettes: from Phylopic.org – Hypsiprymnodon moschatus and Setonix brachyurus by T. Michael Keesey (S. brachyurus photo taken by Sean Mack), Bettongia lesueur by Carly Monks, Notamacropus eugenii by Geoff Shaw, Potorous tridactylus by Rachael T. Mason, Wallabia bicolor by Michael Scroggle; images available for reuse under the Attribution-ShareAlike 3.0 Unported license \u003ca href=\"https://creativecommons.org/licenses/by-sa/3.0/\" target=\"_blank\"\u003ehttps://creativecommons.org/licenses/by-sa/3.0/\u003c/a\u003e). All other silhouettes created by BJ using Inkscape, 2020 (see legend for Fig. 1)\u003cem\u003e. \u003c/em\u003eFigure created in Adobe Illustrator by Science Graphic Design (sciencegraphicdesign.com)\u003c/p\u003e","description":"","filename":"JonesJanisFig4.png","url":"https://assets-eu.researchsquare.com/files/rs-4006700/v1/55e74cacf9d1b2745f8dffc5.png"},{"id":52062604,"identity":"e762284e-5508-4e5d-9f7d-cfdc74e12587","added_by":"auto","created_at":"2024-03-06 05:50:59","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":661282,"visible":true,"origin":"","legend":"\u003cp\u003eCranial views of kangaroo feet, anterior to the top, digits II and III not depicted. \u003cstrong\u003ea.\u003c/strong\u003e \u003cem\u003eProtemnodon brehus\u003c/em\u003e AMNM 145501; \u003cstrong\u003eb.\u003c/strong\u003e \u003cem\u003eMacropus giganteus,\u003c/em\u003e NMV C5532; \u003cstrong\u003ec.\u003c/strong\u003e \u003cem\u003eDendrolagus inustus,\u003c/em\u003e UMZC A12.72/1. Scale bars = 5 cm. Figure created in Procreate by Science Graphic Design (sciencegraphicdesign.com)\u003c/p\u003e","description":"","filename":"JonesJanisFig5.png","url":"https://assets-eu.researchsquare.com/files/rs-4006700/v1/ef07b94100ae64496aca11f0.png"},{"id":52062608,"identity":"4615ff41-cbeb-4984-891f-92c75a470838","added_by":"auto","created_at":"2024-03-06 05:50:59","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1036740,"visible":true,"origin":"","legend":"\u003cp\u003eIntermediate pedal phalanges of fourth digit of macropodids, derived from CT scans, in cranial view and lateral view, proximal to the top. \u003cstrong\u003ea.\u003c/strong\u003e \u003cem\u003eProtemnodon brehus,\u003c/em\u003e AMNM 145501; \u003cstrong\u003eb.\u003c/strong\u003e \u003cem\u003eMacropus giganteus,\u003c/em\u003e AMNH 2390; \u003cstrong\u003ec.\u003c/strong\u003e \u003cem\u003eSthenurus stirlingi,\u003c/em\u003e AMNH 117494A; \u003cstrong\u003ed.\u003c/strong\u003e \u003cem\u003eDorcopsis hageni,\u003c/em\u003e NMS unnumbered; \u003cstrong\u003ee.\u003c/strong\u003e \u003cem\u003eDendrolagus inustus\u003c/em\u003e, UMZC A12.72/1. Scale bars = 1 cm. Figure created in Adobe Illustrator by Science Graphic Design (sciencegraphicdesign.com)\u003c/p\u003e","description":"","filename":"JonesJanisFig6.png","url":"https://assets-eu.researchsquare.com/files/rs-4006700/v1/0c734c1cdbaa0598f7ae98b2.png"},{"id":52062600,"identity":"a46fab51-ebb9-46ef-a564-f6124ddb5592","added_by":"auto","created_at":"2024-03-06 05:50:58","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":1349919,"visible":true,"origin":"","legend":"\u003cp\u003eLateral view of kangaroo phalanges of the fourth pedal digit in natural articulation. \u003cstrong\u003ea.\u003c/strong\u003e \u003cem\u003eProtemnodon brehus,\u003c/em\u003e AMNM 145501; \u003cstrong\u003eb.\u003c/strong\u003e \u003cem\u003eProtemnodon anak, \u003c/em\u003eNMV P38132 (the inset shows the bones placed flat against the ground); \u003cstrong\u003ec. \u003c/strong\u003e\u003cem\u003eSthenurus stirlingi,\u003c/em\u003eNMV P150282.2-4; \u003cstrong\u003ed.\u003c/strong\u003e \u003cem\u003eMacropus giganteus,\u003c/em\u003e NMV C5532; \u003cstrong\u003ee.\u003c/strong\u003e \u003cem\u003eDendrolagus inustus,\u003c/em\u003e UMZC A12.72/1. Scale bars = 3 cm. Figure created in Procreate by Science Graphic Design (sciencegraphicdesign.com)\u003c/p\u003e","description":"","filename":"JonesJanisFig7.png","url":"https://assets-eu.researchsquare.com/files/rs-4006700/v1/900646db7313806386c118eb.png"},{"id":52062602,"identity":"60dd172a-aab6-4da9-a588-369ccbcb8aa1","added_by":"auto","created_at":"2024-03-06 05:50:58","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":363848,"visible":true,"origin":"","legend":"\u003cp\u003eCranial views of kangaroo sacra, anterior to top. \u003cstrong\u003ea\u003c/strong\u003e. \u003cem\u003eProtemnodon brehus\u003c/em\u003e, SAM unnumbered, Salt Creek, Normanville (Pleistocene); \u003cstrong\u003eb.\u003c/strong\u003e \u003cem\u003eMacropus\u003c/em\u003e cf. \u003cem\u003eM. giganteus\u003c/em\u003e, SAM P17495, Green Waterhole (Pleistocene); \u003cstrong\u003ec.\u003c/strong\u003e \u003cem\u003eSimosthenurus occidentalis\u003c/em\u003e, SAM P18308, Green Waterhole (Pleistocene). These sacra come from animals of similar body size (femoral length). Scale bar = 5 cm. Figure created in Procreate by Science Graphic Design (sciencegraphicdesign.com)\u003c/p\u003e","description":"","filename":"JonesJanisFig8.png","url":"https://assets-eu.researchsquare.com/files/rs-4006700/v1/0369d0ac31ffbd3cf333d17c.png"},{"id":52062609,"identity":"992e9765-92b4-4e6d-af9e-58f5655fbe93","added_by":"auto","created_at":"2024-03-06 05:51:00","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":763298,"visible":true,"origin":"","legend":"\u003cp\u003eProposed new restoration of Protemnodon anak based on the anatomical evidence presented in this study. Average adult female human for size comparison (1.66 m). Also shown for comparison is Osphranter rufus, the largest species of kangaroo today\u003cem\u003e. \u003c/em\u003eFigure created in Adobe Illustrator by Science Graphic Design (sciencegraphicdesign.com)\u003c/p\u003e","description":"","filename":"JonesJanisFig9.png","url":"https://assets-eu.researchsquare.com/files/rs-4006700/v1/508d68408627b0de76c6fe3c.png"},{"id":59899751,"identity":"95c39d1d-e5b8-49e8-a218-d0e06d125d4a","added_by":"auto","created_at":"2024-07-09 05:17:45","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7883216,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4006700/v1/01bf2ea0-e1f1-4c39-89de-977ba3694150.pdf"},{"id":52062605,"identity":"5f627b1c-ab37-4902-adc1-a9da955e256c","added_by":"auto","created_at":"2024-03-06 05:50:59","extension":"doc","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":422400,"visible":true,"origin":"","legend":"\u003cp\u003eOnline Resource 1: Supplementary tables.\u003c/p\u003e","description":"","filename":"JonesandJanisOnlineResource1.doc","url":"https://assets-eu.researchsquare.com/files/rs-4006700/v1/3d297c869948848cb5976a04.doc"},{"id":52062603,"identity":"72bdb44b-003a-4f1e-a28c-b05102c44b9d","added_by":"auto","created_at":"2024-03-06 05:50:59","extension":"doc","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":13444096,"visible":true,"origin":"","legend":"\u003cp\u003eOnline Resource 2: Phylogenetic analysis of principal components analysis\u003c/p\u003e","description":"","filename":"JonesandJanisOnlineresource2.doc","url":"https://assets-eu.researchsquare.com/files/rs-4006700/v1/2e9de26050c0bbb29b928edc.doc"}],"financialInterests":"No competing interests reported.","formattedTitle":"Hop, Walk or Bound? Limb Proportions in Kangaroos and the Probable Locomotion of the extinct genus Protemnodon","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe conventional view of a kangaroo (superfamily Macropodoidea) is of a relatively large animal that locomotes via hopping (also referred to as bipedal saltation or ricochetal locomotion). Indeed, the \u0026ldquo;poster child\u0026rdquo; of kangaroos is the red or Eastern grey kangaroo (\u003cem\u003eOsphranter rufus\u003c/em\u003e and \u003cem\u003eMacropus giganteus\u003c/em\u003e, respectively): however, members of Macropodoidea encompass a range of sizes and locomotor modes. Today, kangaroos (macropodoids, kangaroos in the broad sense) range from body masses of 500 g (\u003cem\u003eHypsiprymnodon moschatus\u003c/em\u003e, the Musky Rat-Kangaroo) to \u0026gt;\u0026thinsp;70 kg (\u003cem\u003eO. rufus\u003c/em\u003e) (Kear et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2008\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWith the exception of \u003cem\u003eH. moschatus\u003c/em\u003e all extant kangaroos use hopping as a fast gait. For slow gaits kangaroos either employ a quadrupedal bound, or some mostly larger species (in the genera \u003cem\u003eMacropus\u003c/em\u003e, \u003cem\u003eOnychogalea\u003c/em\u003e, \u003cem\u003eOsphranter\u003c/em\u003e, and \u003cem\u003eWallabia\u003c/em\u003e) employ a \u0026ldquo;pentapedal walk\u0026rdquo; where the tail is used as a fifth limb in supporting the body (Dawson et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Some species have abandoned hopping almost entirely to become primarily quadrupedal: for example, the tree kangaroos (\u003cem\u003eDendrolagus\u003c/em\u003e spp.) hop intermittently when on the ground but usually bound or use a four-footed walk, the latter gait being used most often along tree branches (Windsor and Dagg \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e1971\u003c/span\u003e). Secondary reliance on quadrupedal locomotion has arisen multiple times within Macropodoidea. Potoroids (rat-kangaroos, Potoroidae) use their forelimbs to dig for food, and so can be termed \u0026ldquo;semi-fossorial\u0026rdquo;, and some potoroids (species of \u003cem\u003ePotorous\u003c/em\u003e and \u003cem\u003eBettongia\u003c/em\u003e) have been observed to climb (Seebeck and Rose \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e1989\u003c/span\u003e). Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows a phylogeny of macropodoids including their mode of locomotion.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eToday the most efficient kangaroos in terms of energy consumption are the largest (\u003cem\u003eOsphranter rufus\u003c/em\u003e, \u003cem\u003eMacropus giganteus\u003c/em\u003e and \u003cem\u003eM. fuliginosus\u003c/em\u003e); during hopping locomotion their oxygen consumption at speeds over 3.9 m/s does not increase with speed, a stark difference to the linear increase in oxygen consumption with speed for similar-sized quadrupedal mammals (Baudinette et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1992\u003c/span\u003e). Nevertheless, even the largest kangaroos, extant or extinct, are small in comparison with quadrupeds of similar ecology; i.e., ungulate placental mammals. Optimum body mass for hopping has in fact been found to be ~\u0026thinsp;50 kg, the average body mass for today\u0026rsquo;s largest kangaroos (Bennett and Taylor \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1995\u003c/span\u003e). As kangaroos increase in body mass they experience unusually high skeletal and tendon stresses (McGowan et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2008\u003c/span\u003e); this ultimately limits locomotor ability with a body mass limit to hopping predicted at 160 kg (Snelling et al. \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the Pleistocene a variety of \u0026ldquo;giant\u0026rdquo; kangaroos existed that attained masses greatly above this optimum, reaching up to 230 kg (Helgen et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2006\u003c/span\u003e), and calling into question their ability to hop. Recent studies have found that the diversity of locomotor modes within Macropodoidea was likely far greater in the past than it is present day. The extinct sthenurines (Macropodidae: Sthenurinae) demonstrate anatomical evidence for a bipedal striding type locomotion (Janis et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), a notion supported by trackway data (Camens and Worthy \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Sthenurine forelimbs were likely not primarily weight-bearing at any gait (Wells and Tedford \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Janis et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Jones et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), and their rigid lumbar region would also make spinal flexion for quadrupedal locomotion difficult (Wells and Tedford \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e1995\u003c/span\u003e). Wagstaffe et al. (\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) found that the resistance to bending stresses are different in the foot bones of similarly sized sthenurines and macropodines, supporting the hypothesis of different modes of locomotion in the two subfamilies.\u003c/p\u003e \u003cp\u003eSeveral extinct macropodid taxa are hypothesized to have been at least semi-arboreal if not fully so. These include species in the Balbaridae (Oligo-Miocene stem macropodoids; Den Boer et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2019\u003c/span\u003e); \u003cem\u003eBohra\u003c/em\u003e, a Pleistocene stem dendrolagine but much larger than extant dendrolagines (tree-kangaroos); (Warburton and Prideaux \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2010\u003c/span\u003e); and a derived Pleistocene macropodin, \u003cem\u003eCongruus kitcheni\u003c/em\u003e, likely related to \u003cem\u003eProtemnodon\u003c/em\u003e (see Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), around the size of an extant grey kangaroos (Warburton and Prideaux \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eOf particular interest here is species in the genus \u003cem\u003eProtemnodon\u003c/em\u003e, a close relative of the \u003cem\u003eMacropus\u003c/em\u003e group of taxa in the Macropodini (i.e., \u003cem\u003eMacropus\u003c/em\u003e, \u003cem\u003eOsphranter\u003c/em\u003e and \u003cem\u003eNotamacropus\u003c/em\u003e) (Llamas et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Although the genus originally was comprised of a miscellany of many different extinct and extant macropods, it is now limited to the smaller New Guinea species (\u003cem\u003eP. otibandus, P. snewini\u003c/em\u003e, ~\u0026thinsp;50kg; Flannery \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e1994\u003c/span\u003e, plus the related \u003cem\u003eNombe nombe\u003c/em\u003e; Kerr and Prideaux \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) and larger Australian species (\u003cem\u003eP. roechus\u003c/em\u003e 160 kg, \u003cem\u003eP. anak\u003c/em\u003e\u0026thinsp;~\u0026thinsp;131 kg, \u003cem\u003eP. brehus\u003c/em\u003e\u0026thinsp;~\u0026thinsp;110 kg; Helgen et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). The locomotor mode of this genus has remained somewhat a mystery, though in recent years more evidence has begun coming to light. The largest species of \u003cem\u003eProtemnodon\u003c/em\u003e approached the body mass limit to hopping. With extremely short feet and long arms their body plan appears unsuited to hopping; nevertheless, it has long been assumed that the larger species of \u003cem\u003eProtemnodon\u003c/em\u003e were consistent hoppers like their \u003cem\u003eMacropus\u003c/em\u003e relatives, although the smaller New Guinea species that have short tibiae have been considered to have been quadrupedal (Kear et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). It has been suggested that the anatomy of the large species of \u003cem\u003eProtemnodon\u003c/em\u003e may also reflect more reliance on quadrupedal locomotion (Den Boer \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Janis et al. (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) and Jones et al. (\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) found that the proximal and distal humeral morphology of \u003cem\u003eProtemnodon\u003c/em\u003e indicates a significantly greater proportion of the body weight was borne on the forelimbs than in extant hopping macropodids, supporting this hypothesis of quadrupedality.\u003c/p\u003e \u003cp\u003eHere we present a study of relative limb proportions within Macropodoidea. Relative limb proportions and limb indices have been widely employed as a functional indicator of locomotor mode in extant and extinct mammals, although to date among large mammals only placentals have been considered (e.g., Van Valkenburgh \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; Croft and Anderson \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Samuels and Van Valkenburgh \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Meachen-Samuels and Van Valkenburgh \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Meachen-Samuels 2012; Samuels et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Shockey et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Dunn \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The use of limb indices (i.e., proportions of one limb relative to another) has relative pros and cons over the use of individual linear measurements (see discussion in Dunn \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2018\u003c/span\u003e): limb indices are considered to be a correlate of the mechanical advantage of the primary locomotor muscles (Samuels and Van Valkenburgh \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Limb indices also eliminate the effects of size, though not allometry (Chen and Wilson \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). One disadvantage is that the data should be collected from a single individual, at least for any given index, which may be difficult given the fragmentary nature of fossils (see discussion below for data problems).\u003c/p\u003e \u003cp\u003eIf an extinct macropodid was employing a mode of locomotion divergent from extant taxa the relative proportions of its limbs will likely reflect this. Thus, the divergent types of locomotion proposed above for sthenurines and large species of \u003cem\u003eProtemnodon\u003c/em\u003e are expected to be apparent in their limb proportions.\u003c/p\u003e \u003cp\u003eThis study will enable a better understanding of macropodoid biodiversity and ecomorphology, especially the locomotor diversity of Pleistocene forms. A potential locomotor mode for large species of \u003cem\u003eProtemnodon\u003c/em\u003e is presented, given the evidence found here and in previous studies (Den Boer \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Janis et al. 2022; Jones et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e"},{"header":"Material and Methods","content":"\u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eInvestigation of macropodoid limb proportions\u003c/span\u003e \u003c/p\u003e \u003cp\u003eMaterials\u003c/p\u003e \u003cp\u003eLinear measurements of macropodoid hindlimbs were taken from Janis et al. (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) and forelimb plus some additional hindlimb data were collected in 2019 by Christine Janis from the South Australian Museum. Data consisted of 89 individuals spanning 52 species (Online Resource 1: Tables S1, S2), encompassing the entire macropodid locomotor and body mass range, comprising all known extant and most extinct genera. Each species was grouped into one of three locomotor modes from information from the literature: saltators (employ a significant amount of saltation, or hopping); sthenurines (included as their own group, assumed to be bipedal striders following Janis et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2014\u003c/span\u003e: \u003cem\u003eProcoptodon gilli\u003c/em\u003e, 54 kg. \u003cem\u003eProcoptodon goliah\u003c/em\u003e, 232 kg, \u003cem\u003eSimosthenurus occidentalis\u003c/em\u003e 118 kg, \u003cem\u003eSthenurus andersoni\u003c/em\u003e 72 kg. \u003cem\u003eS. stirlingi\u003c/em\u003e 173 kg, \u003cem\u003eS. tindalei\u003c/em\u003e, 127 kg; body masses from Helgen et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2006\u003c/span\u003e); and quadrupedal, comprising habitual quadrupeds (engaging in little to no saltation but capable of this gait, including tree-kangaroos) and obligate quadrupeds (\u003cem\u003eH. moschatus\u003c/em\u003e). Extinct \u003cem\u003eMacropus\u003c/em\u003e species (\u003cem\u003eM. titan\u003c/em\u003e) were assumed to be saltators. \u003cem\u003eProtemnodon\u003c/em\u003e species (\u003cem\u003eP. anak\u003c/em\u003e\u0026thinsp;~\u0026thinsp;131 kg, \u003cem\u003eP. brehus\u003c/em\u003e\u0026thinsp;~\u0026thinsp;110 kg: body masses from Helgen et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2006\u003c/span\u003e) were included as unknowns.\u003c/p\u003e \u003cp\u003eMethods\u003c/p\u003e \u003cp\u003eThe degree of completeness of the measurements varied between individuals. Several additional measurements were taken in ImageJ to the nearest 0.01 mm (Schneider et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), using high-resolution photographs taken by CMJ. All measurements were taken three times and an average calculated to ensure maximum accuracy.\u003c/p\u003e \u003cp\u003eSixteen linear measurements (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) were combined into a set of thirteen osteological indices (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Some of the indices were adopted from previous studies (see previous list of authors), whereas others are novel to this study. The number of indices that could be calculated for each individual for extinct taxa varied greatly according to the measurements available. All indices were calculated from single individuals except for a couple of extinct taxa (\u003cem\u003eProcoptodon gilli\u003c/em\u003e and \u003cem\u003eProtemnodon anak\u003c/em\u003e, see Online Resource 1, Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Although caution is warranted when using indices, due to the inability to control the effects of the denominator on the numerator and an inability to control for allometric effects (Dunn \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), previous studies using indices (see above list) have nevertheless produced strong ecomorphological interpretations. Variation in the denominator and numerator between species was checked in this study to ensure values for each taxon were comparable.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eList of the 13 osteological indices used in this study. See Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e for the abbreviations for the names of the bones. Bolded indices indicate those featured in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIndex (Abbreviation)\u003c/p\u003e \u003cp\u003eForelimb\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCalculation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFunctional significance\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBrachial Index (BI)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(U1/H1) x 100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRelative length of the forearm. Longer distal limb segments increase stride length. Longer proximal limb segments increase power during grasping and pulling (e.g., Richards et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEpicondyle index (EI)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(H4\u0026thinsp;+\u0026thinsp;H3/H1) x 100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eA measure of the volume of the carpal and digital flexor muscles (e.g., Samuels et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Indicates capacity to manipulate items with the hands.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHumeral Robustness Index (HRI)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(H2/H1) x 100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMeasure of the ability of the humerus to resist bending stresses (e.g., Echeverr\u0026iacute;a et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2014\u003c/span\u003e); thus, an indication of the degree of weight bearing on the forelimbs.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOlecranon Process Index (OPI)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(U2/U1) x 100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRelates to the mechanical advantage of the triceps brachii muscle; a measure of the power of extension of the forelimb (e.g., Dunn \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRadial Index (RI)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(R1/R2) x 100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMeasure of the propensity for forearm supination. Higher values mean a more oval-shaped radial head and a restricted humero-radial joint (e.g., Dunn \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHindlimb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCrural Index (CI)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(T1/F1) x 100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRelative length of the tibia. A longer distal hindlimb increases effective stride length and allows for a longer gastrocnemius (Achilles) tendon, the main tendon in elastic energy storage in macropodids. As used in Chen and Wilson (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIntermediate Phalanx Index (IPI)*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(Ph2-L/Ph2-W) x 100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eA measure of the length of the intermediate phalanx, independent of the length of the whole foot.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMetatarsal Index (MI)*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(Mt4-1/Mt4-2) x 100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eA measure of the relative length of the metatarsal, independent of the length of the hindlimb.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMetatarsal-Femur Index (MFI)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(Mt4-1/F1) x 100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRelative length of the metatarsals (assuming femur length does not vary greatly between locomotor modes). A traditional measure of cursoriality and locomotor performance (e.g., Garland and Janis \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e1993\u003c/span\u003e).\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMetatarsal-Hindlimb Index (MHI)*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(Mt4-1/F1\u0026thinsp;+\u0026thinsp;T1\u0026thinsp;+\u0026thinsp;Mt4-1) x 100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eA measure of the proportion of the hindlimb taken up by the metatarsal.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProximal Phalanx Index (PPI)*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(Ph1-L/ Ph1-W) x 100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eA measure of the length of the proximal phalanx, independent of the length of the whole foot.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eForelimb-Hindlimb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIntermembral Index (IM)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(H1\u0026thinsp;+\u0026thinsp;U1/F1\u0026thinsp;+\u0026thinsp;T1\u0026thinsp;+\u0026thinsp;Mt4-1) x 100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRelative length of the forelimb versus the hindlimb. A measure of quadrupedality: fore- and hindlimbs are similar in length in quadrupeds. Forelimbs are reduced in size in bipeds. Often used in the study of primates (e.g., Granatosky \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eUlna-Femur Index (UFI)*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(U1/F1) x 100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eA measure of the relative length of the ulna independent of overall forelimb length.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eCalculations made based on the linear measurements shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. *Indicates an index that is novel to this study.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe thirteen indices were subjected to analyses to determine the degree to which each discriminated between the locomotor groups and the placement of the \u003cem\u003eProtemnodon\u003c/em\u003e species relative to the defined groups. The performance of the best seven indices is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, but all were used in creating the principal components analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). All statistical tests were carried out in IBM SPSS Statistics v.26 (IBM Corp \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Kolmogorov-Smirnov (for indices where sample size was more than 50; Smirnov \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e1939\u003c/span\u003e) and Shapiro-Wilks (for a sample size of less than 50; Shapiro and Wilk \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e1965\u003c/span\u003e) tests were carried out on the indices to test for normality. ANOVA and Kruskal-Wallis tests (Fisher \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e1934\u003c/span\u003e; Kruskal and Wallis \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e1952\u003c/span\u003e) were then applied depending on the normality of the index to test whether there were significant differences between the locomotor groups. Due to increased risk of type I error when running multiple tests simultaneously results were adjusted using the Bonferroni correction (Bonferroni \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1935\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe following analyses were undertaken in RStudio (RStudio Team \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). To reduce dimensionality and visualize the data, allowing easy comparison of \u003cem\u003eProtemnodon\u003c/em\u003e species to the groups of known locomotor mode, a principal component analysis (PCA) was undertaken using the PCA function in the package FactoMineR (L\u0026ecirc; et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). The dataset was pruned to include only those taxa (22) for which all indices were available: for the PCA only \u003cem\u003eProtemnodon anak\u003c/em\u003e was comprised of several individuals, all from the Museum Victoria (Melbourne) collections and from the same locality (Morwell, Victoria). Fortunately, this did not impact the dataset range of body mass, locomotor mode and taxonomic diversity. A phylogenetic correction analysis (see Online Resource 2) showed little significant effects of phylogeny.\u003c/p\u003e \u003cp\u003eMuseum abbreviations\u003c/p\u003e \u003cp\u003eAMNH\u0026thinsp;=\u0026thinsp;American Museum of Natural History, New York, USA. NHMUK\u0026thinsp;=\u0026thinsp;Natural History Museum, London, UK. NMS\u0026thinsp;=\u0026thinsp;National Museum of Scotland, Edinburgh, UK. NMV\u0026thinsp;=\u0026thinsp;Museum Victoria, Melbourne, Australia. SAM\u0026thinsp;=\u0026thinsp;South Australian Museum, Adelaide, Australia. UMCZ\u0026thinsp;=\u0026thinsp;University Museum of Zoology, Cambridge, UK.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eThe indices varied in their ability to distinguish between the locomotor groups. The functional significance of each index is explained in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Some other indices (e.g., radial index, epicondyle index) showed very little differentiation among the groups and are not shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and Online Resource 1, Table \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e; others showed clear distinctions. We present here the indices that show the clearest distinctions between taxa: other indices are shown and discussed in Jones \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2020\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eLimb Indices\u003c/span\u003e \u003c/p\u003e \u003cp\u003eSaltators and sthenurines have consistent values of Metatarsal-Femur Index (MFI \u0026ndash; relative length of the metatarsal to the femur, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea) above 40. The largest extant kangaroos achieve values of around 60\u0026ndash;76 (e.g., \u003cem\u003eOsphranter rufus\u003c/em\u003e, #12, MFI: 75.8), reflecting a metatarsal more than two-thirds the length of the femur, but the extinct giant kangaroo, \u003cem\u003eM. titan\u003c/em\u003e, #16, has a relatively low index (58.86) in comparison with other extant large species. Quadrupedal macropodids show lower values, with the lowest values occurring in the tree-kangaroos (e.g., \u003cem\u003eDendrolagus matschei\u003c/em\u003e, #73, 28.2). \u003cem\u003eProtemnodon\u003c/em\u003e species (only the large ones \u003cem\u003eP. anak\u003c/em\u003e and \u003cem\u003eP. brehus\u003c/em\u003e are included here) have values most comparable to the quadrupeds (\u003cem\u003eP. anak\u003c/em\u003e, 36.38, #89, but \u003cem\u003eP. brehus\u003c/em\u003e, #90, has a slightly higher value, 44.73). Quadrupedal taxa and \u003cem\u003eProtemnodon\u003c/em\u003e species were significantly different (lower index) from both saltators and sthenurines (see Table \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e). Patterns similar to MFI occur in other indices in Jones \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2020\u003c/span\u003e (Proximal Phalanx Index, Intermediate Phalanx Index, Metatarsal Index and Metatarsal-Hindlimb Index).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIntermembral Index (IM \u0026ndash; relative length of the forelimb to the hind limb, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb) was consistently below 51 for saltators, reflecting hindlimbs over double the length of the forelimbs. Similar values were seen in the sthenurines and in the terrestrial quadrupedal macropodids (potoroids, \u003cem\u003eSetonix\u003c/em\u003e, \u003cem\u003eDorcopsis\u003c/em\u003e), although these taxa tended to have somewhat higher values than most of the saltators. Conversely, the obligate quadrupedal bounder (\u003cem\u003eHypsiprymnodon moschatus\u003c/em\u003e, #85, IM\u0026thinsp;=\u0026thinsp;57.85) and the tree-kangaroos showed much higher values (e.g., \u003cem\u003eDe. goodfellowi\u003c/em\u003e, #69, IM\u0026thinsp;=\u0026thinsp;69.90). The high values of the tree-kangaroos reflect adaptations to arboreality, with both relatively longer forelimbs and shorter hind limbs (Warburton \u0026amp; Prideaux \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The \u003cem\u003eProtemnodon\u003c/em\u003e species have values most comparable to the obligate quadrupedal bounder \u003cem\u003eH. moschatus\u003c/em\u003e.\u003c/p\u003e \u003cp\u003eCrural Index (CI \u0026ndash; relative length of the tibia to the femur, Fig, 3c) shows values over 120 in the saltators and the sthenurines, indicating a relatively long tibia. The largest extant kangaroos have a tibia more than twice the length of their femur (e.g., \u003cem\u003eMacropus fuliginosus\u003c/em\u003e, #2, CI\u0026thinsp;=\u0026thinsp;226.52), and have relatively longer tibiae than sthenurines (see Janis et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Tree-kangaroos possess the lowest CI (e.g., \u003cem\u003eDe. dorianus\u003c/em\u003e, #68, CI\u0026thinsp;=\u0026thinsp;97.8); their femur and tibia show little to no differentiation in length. Low values occur across the quadrupedal group (e.g., \u003cem\u003eH. moschatus\u003c/em\u003e, #85, CI\u0026thinsp;=\u0026thinsp;110.90; \u003cem\u003eS. brachyurus\u003c/em\u003e, #78, CI\u0026thinsp;=\u0026thinsp;115.3), with the exception of the dorcopsids (e.g., \u003cem\u003eDorcopsis muelleri\u003c/em\u003e, 98, CI\u0026thinsp;=\u0026thinsp;141.70). \u003cem\u003eProtemnodon\u003c/em\u003e species have relatively high values of CI (e.g., \u003cem\u003ePr. brehus\u003c/em\u003e, # 90, CI\u0026thinsp;=\u0026thinsp;168.23). Quadrupedal taxa were statistically different (lower index) from saltators, sthenurines and \u003cem\u003eProtemnodon\u003c/em\u003e species (see Online Resource 1, Table S3).\u003c/p\u003e \u003cp\u003eOlecranon process index (OPI \u0026ndash; relative length of the olecranon process to the shaft of the ulna, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). Sthenurines have a notably low OPI (~\u0026thinsp;10\u0026ndash;13) and can be statistically distinguished from quadrupedal taxa and \u003cem\u003eProtemnodon\u003c/em\u003e species (OPI\u0026thinsp;~\u0026thinsp;18\u0026ndash;21) (see Online Resource 1, Table S3). Most saltating macropodid taxa also have a low OPI (~\u0026thinsp;10\u0026ndash;17), but the semi-fossorial potoroids show much higher values (e.g., \u003cem\u003eAepyprymnus rufescens\u003c/em\u003e, #49, OPI\u0026thinsp;=\u0026thinsp;26.00; \u003cem\u003eBettongia lesueur\u003c/em\u003e, #51, OPI\u0026thinsp;=\u0026thinsp;20.44; \u003cem\u003ePotorous longipes\u003c/em\u003e, #83, OPI\u0026thinsp;=\u0026thinsp;23.02). Interestingly, the OPI of the \u003cem\u003eProtemnodon\u003c/em\u003e species is relatively high, in particular \u003cem\u003ePr. brehus\u003c/em\u003e (#90, OPI\u0026thinsp;=\u0026thinsp;21.18), with values comparable to those of \u003cem\u003eB. lesueur\u003c/em\u003e and \u003cem\u003ePo. longipes\u003c/em\u003e.\u003c/p\u003e \u003cp\u003eHumeral robustness index (HRI \u0026ndash; relative midshaft diameter of the humerus relative to its articular length, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee) shows the highest values (HRI\u0026thinsp;~\u0026thinsp;10\u0026ndash;13) in tree-kangaroos (#s 69, OPI\u0026thinsp;=\u0026thinsp;10.65 and 72, OPI\u0026thinsp;=\u0026thinsp;11.21) and in both semi-fossorial (e.g., \u003cem\u003eB. lesueur\u003c/em\u003e, #51, OPI\u0026thinsp;=\u0026thinsp;11.79) and quadrupedal (e.g., \u003cem\u003eDo. luctuosa\u003c/em\u003e, #78, OPI\u0026thinsp;=\u0026thinsp;13.13) taxa. However, some saltators (\u003cem\u003eNotamacropus eugenii\u003c/em\u003e, #11, OPI\u0026thinsp;=\u0026thinsp;11.0; \u003cem\u003eOnychogalea fraenata\u003c/em\u003e, #40, OPI\u0026thinsp;=\u0026thinsp;12.88; \u003cem\u003eLagostrophus fasciatus\u003c/em\u003e, #46, OPI\u0026thinsp;=\u0026thinsp;13.19) also have high values; the reason for this is not clear, and most saltators have values less than 10.5. \u003cem\u003eProtemnodon\u003c/em\u003e species also exhibit some of the highest HRI values (\u003cem\u003ePr. brehus\u003c/em\u003e, #90, OPI\u0026thinsp;=\u0026thinsp;12.45, although the difference between \u003cem\u003ePr. brehus\u003c/em\u003e and \u003cem\u003ePr. anak\u003c/em\u003e (#s 86 and 87, OPIs\u0026thinsp;=\u0026thinsp;10.15 and 10.47) may reflect different sexes and sexual dimorphism rather than functional differences.\u003c/p\u003e \u003cp\u003eUlna-Femur (UFI \u0026ndash; relative length of the ulna to the femur; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eF) and reflects elongation of the distal forelimb. The highest UFI values (\u0026gt;\u0026thinsp;70) are seen in the tree-kangaroos, the sthenurines and especially in the \u003cem\u003eProtemnodon\u003c/em\u003e species. High values are also seen in the large macropodids, and in \u003cem\u003eNotamacropus dorsalis\u003c/em\u003e (#19, a male specimen). The \u003cem\u003eProtemnodon\u003c/em\u003e species are significantly different (higher) from the saltators (despite the high values of the large saltators), and the quadrupedal species (see Online Resource 1, Table S3).\u003c/p\u003e \u003cp\u003eBrachial Index (BI \u0026ndash; relative length of the ulna to the humerus; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg). This index also reflects elongation of the distal forelimb but relative to the proximal forelimb rather than to the femur. The lowest values of BI (\u0026lt;\u0026thinsp;110) occur in the tree-kangaroos and the large sthenurine \u003cem\u003eS. stirling\u003c/em\u003e (#63, BI\u0026thinsp;=\u0026thinsp;112.65), reflecting a relatively long humerus and short forearm. In contrast high values (\u0026gt;\u0026thinsp;135), reflecting a longer forearm relative to the humerus, are seen in the large saltators, \u003cem\u003eProtemnodon\u003c/em\u003e species (especially \u003cem\u003ePr. anak\u003c/em\u003e, #s 86, 87, BI\u0026thinsp;=\u0026thinsp;145.8) and, perhaps surprisingly, in the small (~\u0026thinsp;50 kg, Helgen et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2006\u003c/span\u003e) sthenurine \u003cem\u003eProcoptodon gilli\u003c/em\u003e (#56, BI\u0026thinsp;=\u0026thinsp;171.13). \u003cem\u003eProtemnodon\u003c/em\u003e species are statistically different from all other locomotor groups (higher index), and the sthenurines are statistically different from the saltators (lower index) (see Online Resource 1, Table S3).\u003c/p\u003e \u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003ePrincipal Components Analysis\u003c/span\u003e \u003c/p\u003e \u003cp\u003eThe first three components of the PCA together explain 76.66% of the total variance. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows a plot of PC1 against PC2 (other PC axes were not significantly different with respect to the sorting of the taxa, see Online Resource 1, Table S4). The first component largely distinguishes the saltators and the sthenurines (positive scores) from the quadrupedal taxa and \u003cem\u003eProtemnodon\u003c/em\u003e species (negative scores). This is because indices reflecting metatarsal length (e.g., Metarsal-Femur Index, MFI) have high positive values on this axis, whereas indices reflecting forelimb length (e.g., Intramembral Index, IM) have high negative values (see Online Resource 1, Table S4). The second component distinguishes \u003cem\u003eProtemnodon\u003c/em\u003e species, the sthenurines and the large specialized saltators (i.e., \u003cem\u003eMacropus\u003c/em\u003e and \u003cem\u003eOsphranter\u003c/em\u003e) (high Crural Index, CI, and Ulna-Femur Index, UFI; positive scores) from the quadrupeds and generalized (lower CI) and semi-fossorial saltators (high Olecranon Process Index, OPI; negative scores). Note: the extremely high score of \u003cem\u003eO. rufus\u003c/em\u003e on PC1 is in part due to sexual dimorphism: this individual (NHMUK 205, #14 in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) is a large male with an extremely high UFI (in contrast, the \u003cem\u003eMacropus giganteus\u003c/em\u003e, NMV C5532, with lower scores on PC1, is a female). The sthenurines have similar scores to the large macropodines on PC1, but are separated from them on PC2, probably due to high UFIs. Although \u003cem\u003eProtemnodon\u003c/em\u003e species possess a high UFI and relatively high CI, giving them high scores on PC1, their divergence from extant large macropodines along PC2 is related to their low MFI and high IM, plus relatively high Humeral Robustness Index.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe results show that osteological indices are a good reflection of primary gait among macropodoids.\u003c/p\u003e \u003cp\u003eLarge \u003cem\u003eProtemnodon\u003c/em\u003e species possess an unusual suit of osteological traits both similar to and different from quadrupedal and saltating extant macropodoids and also from the potentially bipedally-striding sthenurines. On the other hand, the sthenurines are similar to the large hopping macropodines in their hindlimb proportions, but differ in their forelimb proportions, likely due to their highly specialized hands reflecting a habit of using the forelimbs to procure food (Tedford \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e1966\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eMetatarsal length shows a strong relationship with primary locomotor mode, in particular when distinguishing between quadrupedal bounders vs. saltators (Kear et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Metatarsal-Femur Index (MFI) is essentially a measure of stride length relative to the power of hindlimb extension (Polly \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Long metatarsals increase stride length (Hildebrand and Goslow \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e1982\u003c/span\u003e) and increase the lever arm for the action of the gastrocnemius tendon, allowing high speed, efficient hopping. More quadrupedal macropodines (e.g., \u003cem\u003eDorcopsis\u003c/em\u003e spp., \u003cem\u003eSetonix\u003c/em\u003e) have relatively short metatarsals in comparison to specialised hoppers like species of \u003cem\u003eMacropus\u003c/em\u003e and \u003cem\u003eOsphranter\u003c/em\u003e, as do tree-kangaroos (\u003cem\u003eDendrolagus\u003c/em\u003e spp.). The short metatarsals of \u003cem\u003eProtemnodon\u003c/em\u003e species, otherwise only seen in more quadrupedal extant kangaroos, must represent a secondary condition from the related \u003cem\u003eMacropus\u003c/em\u003e complex extant macropodines, and are a strong indication they no longer relied on saltation as a dominant mode of locomotion. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows the feet of \u003cem\u003eProtemnodon brehus\u003c/em\u003e in comparison with a specialized hopper (\u003cem\u003eM. giganteus\u003c/em\u003e) and a tree-kangaroo (\u003cem\u003eD. inustus\u003c/em\u003e), showing not only the short metatarsals of \u003cem\u003eProtemnodon\u003c/em\u003e, but also the highly divergent fifth digit, more divergent than in the tree-kangaroo with similarly short metatarsals (although tree-kangaroos have relatively longer and more robust fifth digits). Sthenurines show fairly elongated metatarsals, but they are not as extremely elongated as those of the large specialized saltators.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIntermembral Index (IM) measures the relative length of the fore- and hindlimbs. Relative lengthening of the hindlimbs in saltators is particularly striking because the forelimbs do not show similar modifications (Hildebrand and Goslow \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e1982\u003c/span\u003e); thus, saltators have low values of IM (Finch and Freedman \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). A higher IM reflects less differentiation in the length of the fore- and hindlimbs, a necessary adaption if consistently walking quadrupedally and especially necessary when living an arboreal lifestyle; therefore, quadrupedal and arboreal macropodoids have high values of IM. With IM values close to that of quadrupedal bounding species (\u003cem\u003eDendrolagus\u003c/em\u003e spp., \u003cem\u003eH. moschatus\u003c/em\u003e), the IMs of the large \u003cem\u003eProtemnodon\u003c/em\u003e species suggest they engaged in consistently more quadrupedal locomotion than extant large kangaroos. Relatively low values of IM in sthenurines are likely a result of the adoption of fully bipedal locomotion, allowing the forelimbs to be specialized for food manipulation only (Janis et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2014\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eElongation of the distal limb is associated with adaptations for locomotor efficiency (Janis and Wilhelm \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1993\u003c/span\u003e). Relative lengthening of the tibia (high Crural Index\u0026thinsp;=\u0026thinsp;CI) is part of the suit of morphological adaptations allowing efficient saltation in macropodoids (Hildebrand and Goslow \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e1982\u003c/span\u003e; Dawson et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), although it is a primarily a feature of the large macropodines (\u0026gt;\u0026thinsp;35 kg) where tibia length scales with positive allometry (Janis et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Increasing the length of the tibia relative to the femur allows for a longer effective side length with little increase in the cost of limb recycling (Dawson and Webster \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), and allows for long gastrocnemius tendons for storage of elastic energy. Note that, while both large \u003cem\u003eProtemnodon\u003c/em\u003e species and sthenurines had long tibiae (sthenurines show a CI almost equivalent to the large hopping macropodines), these tibiae were still somewhat shorter than in the large extant macropodines (Janis et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Although large \u003cem\u003eProtemnodon\u003c/em\u003e species were likely too big and robust to be built for speed, retention of the long tibia from their macropodine ancestors indicates they may have benefited from the increased efficiency a longer distal hind limb provides with respect to maintaining an increased stride length (see discussion in Janis et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eNevertheless, the long tibiae of large species of \u003cem\u003eProtemnodon\u003c/em\u003e remain a puzzling feature, especially as the smaller New Guinea species had short tibiae (Kear et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), although the similarly sized Pliocene Australian species \u003cem\u003eP. snewini\u003c/em\u003e did not (Bartholomai \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1978\u003c/span\u003e). Extreme elongation of the tibia in large macropodines precludes their ability to employ a quadrupedal bound, necessitating adoption of the pentapedal walk at slow speeds (Dawson et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Pentapedal locomotion is an extremely inefficient gait, more so than quadrupedal bounding (Bennett \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). Positive correlation between body mass and time spent active for herbivores (Belovsky and Slade \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1986\u003c/span\u003e) indicates a large animal such as \u003cem\u003eProtemnodon\u003c/em\u003e would favour an efficient slow gait for foraging, but the large macropodines are restricted to using the inefficient pentapedal gait for this behaviour. The IM of large \u003cem\u003eProtemnodon\u003c/em\u003e species is consistently greater than that of the pentapedal extant macropodines, indicating that they could have used a more efficient form of slow locomotion. A combination of long forelimbs and short feet may have allowed \u003cem\u003eProtemnodon\u003c/em\u003e species to circumvent the constraints a high CI poses to extant macropodines, necessitating pentapedal walking (Dawson et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Indeed, the relatively long distal transverse and mammillary processes the anterior caudal vertebrae (as seen in \u003cem\u003ePr. anak\u003c/em\u003e, NMV 39105) appear to indicate lack of weight-bearing tail use during locomotion (pers. obs. following Dawson \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), although this requires further investigation.\u003c/p\u003e \u003cp\u003eNonetheless, it appears \u003cem\u003eProtemnodon\u003c/em\u003e species were not entirely prioritising locomotor efficiency. The Olecranon Process Index (OPI) of \u003cem\u003eProtemnodon\u003c/em\u003e species, in particular \u003cem\u003ePr. brehus\u003c/em\u003e, is remarkably similar to that of semi-fossorial potoroids. A longer olecranon process (high OPI) produces a greater mechanical advantage of the triceps brachii muscle (Dunn \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), allowing the production of higher output forces from the forelimbs, a necessity for digging into the substrate. A shorter olecranon process allows full extension of the elbow, increasing forelimb length and stride length (Rodman \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e1979\u003c/span\u003e). Wells and Tedford (\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e1995\u003c/span\u003e) note that the short olecranon processes of sthenurines (reflected here in their low OPI) would allow for arm extension during feeding. Large \u003cem\u003eProtemnodon\u003c/em\u003e species appear to have been prioritizing forelimb power over stride length and this may be indicative that they engaged in digging (as proposed by Moore \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Furthermore, the robustness of a bone relates to its ability to resist the bending forces associated with either supporting the body weight or developing forces for specific limb functions, e.g., digging (Elissamburu and de Santis \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Digging behaviour is also reflected in the high Humeral Robustness Index (HRI) of large \u003cem\u003eProtemnodon\u003c/em\u003e species, though this may be associated with increased quadrupedalism alone. It is interesting that the distal humeral morphology of large \u003cem\u003eProtemnodon\u003c/em\u003e species is similar to that of the common wombat (\u003cem\u003eVombatus ursinus\u003c/em\u003e) (Jones et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Figueirido et al. (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) note the greater degree of forelimb stabilization in the wombat may relate to its semi-fossorial nature. Restriction of the forelimb to parasagittal movement is advantageous for digging as it prevents dislocation of the joint under pressure (Moore \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2008\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIt is therefore entirely possible that the combination of features of a high degree of forelimb stabilization, large olecranon process and robust forelimbs of \u003cem\u003eProtemnodon\u003c/em\u003e evince adaptations for digging. The short feet, with a divergent fifth digit (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) and hooked phalanges (see below) would also have provided a stable base for this activity. Moore (\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) noted additional morphological similarities between \u003cem\u003eProtemnodon\u003c/em\u003e species and the burrower \u003cem\u003eBettongia. lesueur\u003c/em\u003e (the boodie), and her discriminant function analysis of macropodoid forelimb anatomy found \u003cem\u003eP. anak\u003c/em\u003e to plot between forage digging and shelter digging macropodoids. However, with no extant analogues it is difficult to distinguish between digging adaptations and simply the necessary adaptations for a large macropodid to bear weight consistently on its forelimbs. In contrast, sthenurines have some of the lowest OPIs of all macropodoids (see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). A small olecranon process limits the ability of the arm to support the anterior body weight on the hands and use the arms for propulsion along the ground (Wells and Tedford \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e1995\u003c/span\u003e), supporting the notion that the sthenurines did not employ their forelimbs during locomotion.\u003c/p\u003e \u003cp\u003eA final interesting feature of large \u003cem\u003eProtemnodon\u003c/em\u003e species (the smaller ones have not been examined), which has not before been noted, is the strange nature of the intermediate pedal phalanges and the posture of the phalanges. The intermediate pedal phalanx is extremely short and broad, with a \u0026ldquo;puffy\u0026rdquo; appearance, very unlike any other macropodoid (see Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). The resistance to bending in the intermediate phalanx of \u003cem\u003eProtemnodon brehus\u003c/em\u003e is different to other large macropodines, showing very little difference in resistance along the length of the bone; in contrast, other macropodines have a definite trough between proximal and distal peaks (Wagstaffe et al. \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). A study of resistance to bending in small macropodids showed a similar resistance pattern in the tree-kangaroo \u003cem\u003eDendrolagus inustus\u003c/em\u003e, but not in any terrestrial taxon (Jones \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe phalanges of large \u003cem\u003eProtemnodon\u003c/em\u003e species have a strange articulation (as observed by CMJ in at least a dozen different specimens, and see also Wagstaffe \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). If placed flat on a surface they cannot be placed in articulation, unlike the condition in other kangaroos. Rather, the natural articulation appears for there to be a \u0026ldquo;hooking\u0026rdquo; between the intermediate and ungual phalanges (see Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). The function of this is not clear, but it likely allowed for a degree of gripping with the feet, enhanced by the long, curved ungual phalanges.\u003c/p\u003e \u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eThe possible locomotor mode of\u003c/span\u003e \u003cspan type=\"ItalicUnderline\" class=\"ItalicUnderline\" name=\"Emphasis\"\u003eProtemnodon\u003c/span\u003e\u003c/p\u003e \u003cp\u003eWhile the superficial anatomy of large \u003cem\u003eProtemnodon\u003c/em\u003e species is clearly that of a kangaroo, their detailed anatomy makes it a puzzling animal. This study has determined that the postcranial anatomy of \u003cem\u003eProtemnodon\u003c/em\u003e is strongly divergent from that of large extant macropodines: large species of \u003cem\u003eProtemnodon\u003c/em\u003e likely could not have employed sustained hopping locomotion like large extant kangaroos, although trackway data do indicate that they hopped at least occasionally (Belperio and Fotheringhamm 1990; Carey et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Aspects of their forelimb anatomy indicate a much greater degree of weight-bearing on the forelimbs than large extant kangaroos, including the morphology of the proximal (Janis et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) and distal humerus (Jones et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Large \u003cem\u003eProtemnodon\u003c/em\u003e species plot in a vacant area of macropodoid morphospace (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), indicating that there are no extant analogues. While the locomotor mode of large \u003cem\u003eProtemnodon\u003c/em\u003e species will never be known for certain, much can be inferred based on the robust morphological observations presented here.\u003c/p\u003e \u003cp\u003eMultiple lines of evidence indicate large \u003cem\u003eProtemnodon\u003c/em\u003e species may have been predominantly quadrupedal. Den Boer (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) noted the general curvature of their ungual phalanges (see Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea, b): making comparisons to extant tree-kangaroos; she concluded this morphology may have provided grip and aided in maintaining balance on irregular substrates. The \u0026ldquo;hooking\u0026rdquo; of the pedal phalanges (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea, b) would also help with this. Given the size of large \u003cem\u003eProtemnodon\u003c/em\u003e species and the forearm motion relatively restricted to the parasagittal plane (Janis et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Jones et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), it is not suggested that they were engaging in arboreal activities (for which they would surely have been too large), but rather an enhancement of locomotion within a closed habitat. Isotopic values in the teeth of a species of \u003cem\u003eProtemnodon\u003c/em\u003e at the Cuddie Springs site indicate a closed habitat ecology (DeSantis et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), and quadrupedal locomotion enables easier directional changes when navigating obstacles in dense forest habitats (Windsor and Dagg \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e1971\u003c/span\u003e). If large \u003cem\u003eProtemnodon\u003c/em\u003e species inhabited woodland or forest, given their size adoption of quadrupedal locomotion may have been necessary to enable navigation of the dense forest floor, using their short, wide feet with divergent fifth digits and hooked toes to gain purchase on the irregular ground. As previously noted, the forearm morphology of large \u003cem\u003eProtemnodon\u003c/em\u003e species is consistent with digging, and the short, broad feet may have aided in gaining purchase during such activities (see Hildebrand and Goslow \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e1982\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA major question remains: were large \u003cem\u003eProtemnodon\u003c/em\u003e species bounding using their hind legs synchronously (as in bounding kangaroos and other small bounding mammals) or asynchronously (i.e., some kind of galloping gait)? Asynchronous use of all four limbs is only seen today in the genus \u003cem\u003eDendrolagus\u003c/em\u003e (Windsor and Dagg \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e1971\u003c/span\u003e). The sacrum of \u003cem\u003eProtemnodon\u003c/em\u003e is unusually large and broad (see Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). Janis et al. (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) interpreted the large, broad sacrum of sthenurines as indicative of walking with alternate limbs, resisting rotational torsion at the sacroiliac joint. Although \u003cem\u003eProtemnodon\u003c/em\u003e species never have more than two sacral vertebrae (as in other macropodids), while sthenurines sometimes have three (as shown here), the sacrum is proportionally much broader and more massive in general even than in sthenurines (see Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). Therefore, the large sacrum of \u003cem\u003eProtemnodon\u003c/em\u003e could also be suggestive of the need to brace against the rotational forces associated with using the hindlimbs independently, perhaps indicating some sort of galloping quadrupedal gait (in contrast to bounding, which uses the hind limbs in synchrony).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eJones et al. (\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) presented a restoration of \u003cem\u003eProtemnodon anak\u003c/em\u003e based on the common way in which the genus is portrayed (from the mounted skeleton of \u003cem\u003ePr. anak\u003c/em\u003e in the South Australian Museum). Using new knowledge gained from this study an alternate restoration of \u003cem\u003eProtemnodon anak\u003c/em\u003e is now proposed (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). While the hypothesis that large species of \u003cem\u003eProtemnodon\u003c/em\u003e may have had a quadrupedal, \u0026lsquo;semi-fossorial\u0026rsquo; lifestyle is necessarily speculative, it is nonetheless grounded in the new understanding of its unique postcranial anatomy gained through this study.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe relative proportions of an macropodid limbs can be shown to be functionally relevant in determining its locomotor mode. Macropodid limb proportions differ significantly between the species specializing in the two different dominant modes of locomotion in extant macropodids: i.e., predominantly quadrupedal or predominantly saltatory. The morphology of the extinct sthenurines and large species of the extinct macropodine \u003cem\u003eProtemnodon\u003c/em\u003e show them to be clearly distinguishable from extant species practicing these two dominant modes of locomotion.\u003c/p\u003e \u003cp\u003eThe results presented support prior hypotheses that macropodid locomotion was more diverse in the past and strengthen previous hypotheses that sthenurines employed bipedal striding and large species of \u003cem\u003eProtemnodon\u003c/em\u003e were predominantly quadrupedal. A quadrupedal, closed habitat lifestyle is suggested for large species of \u003cem\u003eProtemnodon\u003c/em\u003e in which they may have used their feet to grip the substrate. Additionally, multiple lines of evidence suggest these \u003cem\u003eProtemnodon\u003c/em\u003e species may have engaged in digging behaviour.\u003c/p\u003e"},{"header":"Declarations","content":" \u003cp\u003e \u003cstrong\u003eCompeting Interests\u003c/strong\u003e \u003cp\u003eNone\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eFunds from the University of Bristol Program in Palaeobiology enabled the scans. Funds to CMJ from the Bushnell Foundation (Brown University) aided in the collection of linear measurement data for the body mass estimations.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eBJ performed the original research from data largely provided from CJ. BJ and CJ wrote the main manuscript and prepared the initial figures (BJ Figs 1-4, 6, 9; CJ 5, 7-8). BJ and CJ reviewed the manuscript\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eWe thank Jin Meng and Judy Galkin (Vertebrate Paleontology) at the American Museum of Natural History (New York, USA) for access to specimens in their care, and Ruth O\u0026rsquo;Leary and Ana Balcarel for facilitating the scans of \u003cem\u003eMacropus giganteus\u003c/em\u003e and \u003cem\u003eSthenurus stirlingi\u003c/em\u003e (and thanks to all, plus Alana Gishlik, for the loan of the foot of \u003cem\u003eProtemnodon brehus\u003c/em\u003e). We thank other museum curators for access to specimens in their care for the measurements used: Jin Meng and Judy Galkin (Vertebrate Paleontology) and Eileen Westwig and Rob McPhee (Mammalogy) at the American Museum of Natural History (New York, USA); Rob Asher and Mathew Lowe at the University of Cambridge Museum of Zoology (Cambridge, UK); Roberto Portela Miguez at the Natural History Museum (London, UK); David Stemmer and Mary-Anne Binnie at the South Australian Museum, Adelaide, Australia. Helen Ryan and Kenny Travouillon at the Western Australian Museum (Perth, Australia); Adam Yates at the Museum and Art Gallery of the Northern Territory (Alice Springs, Australia); Tim Ziegler and Karen Roberts at the Museum Victoria, Melbourne, Australia); Sandy Ingleby and Anja Divaljan (Australian Museum, Sydney, Australia); Kirsten Spring and Scott Hocknull (Queensland Museum, Brisbane, AUS). For the scanning of the loaned specimens at the University of Bristol we thank Tom Davies and Liz Martin-Silverstone. For the figures, we thank Nuria Melisa Morales-Garc\u0026iacute;a and Emily Green at Science Graphic Design.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e \u003cp\u003eAll data generated or analyzed during this study are included in this published article and its supplementary information files\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBartholomai A (1978) The Macropodidae (Marsupialia) from the Allingham Formation, northern Queensland; results of the Ray E Lemley expedition, Part 2. Mem Queensl Mus 18:127\u0026ndash;143\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBaudinette R, Snyder GK, Frappell PB (1992) Energetic cost of locomotion in the tammar wallaby. Am J Physiol-Reg I 262:R771\u0026ndash;R778 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1152/ajpregu.1992.262.5.R771\u003c/span\u003e\u003cspan address=\"10.1152/ajpregu.1992.262.5.R771\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBelovsky GE, Slade J (1986) Time budgets of grassland herbivores: body size similarities. Oecol 70:53\u0026ndash;62 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/BF00377110\u003c/span\u003e\u003cspan address=\"10.1007/BF00377110\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBelperio AP, Fotheringham DG (1990) Geological setting of two quaternary footprint sites, western South Australia. Aust J Earth Sci 37:37\u0026ndash;42 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/08120099008727903\u003c/span\u003e\u003cspan address=\"10.1080/08120099008727903\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBennett M (2000) Unifying principles in terrestrial locomotion: do hopping Australian marsupials fit in? Physiol Biochem Zool 73:726\u0026ndash;735 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1086/318110\u003c/span\u003e\u003cspan address=\"10.1086/318110\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBennett MB, Taylor CR (1995) Scaling of elastic strain energy in kangaroos and the benefits of being big. Nature 378:56\u0026ndash;59\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBonferroni CE (1935) Il calcolo delle assicurazioni su gruppi di teste. In: Carboni SO (ed) Onore del Professore Salvatore Ortu Carboni. Bardi, Rome, pp 13\u0026ndash;60\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCamens AB, Worthy TH (2019) Walk like a kangaroo: new fossil trackways reveal a bipedally striding macropodid in the Pliocene of Central Australia. J Vertebr Paleontol, Programs and Abstracts 2019:72\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCarey SP, Camens AB, Cupper ML, Grun R, Hellstrom JC, McKnight SW, McLennan I, Pickering DA, Trusler M, Aubert M (2011) A diverse Pleistocene marsupial trackway assemblage from the Victorian Volcanic Plains. Australia Quaternary Sci Rev 30:591\u0026ndash;610 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.quascirev.2010.11.021\u003c/span\u003e\u003cspan address=\"10.1016/j.quascirev.2010.11.021\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen M, Wilson GP (2015) A multivariate approach to infer locomotor modes in Mesozoic mammals. Paleobiology 4:280\u0026ndash;312 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1017/pab.2014.14\u003c/span\u003e\u003cspan address=\"10.1017/pab.2014.14\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCroft DA, Anderson LC (2008) Locomotion in the extinct notoungulate \u003cem\u003eProtypotherium\u003c/em\u003e. Palaeontol Electron, 1111A, 1\u0026ndash;20\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDawson RS (2015) Morphological correlates of pentapedal locomotion in kangaroos and wallabies (Family: Macropodidae). Dissertation, The University of Western Australia, Perth\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDawson RS, Warburton NM, Richards HL, Milne N (2015) Walking on five legs: investigating tail use during slow gait in kangaroos and wallabies. Aust J Zool 63:192\u0026ndash;200 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1071/ZO15007\u003c/span\u003e\u003cspan address=\"10.1071/ZO15007\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDawson TJ, Webster K (2010) Energetic characteristics of macropodoid locomotion. In: Coulson G, Eldridge MDB (eds) Macropods: The Biology of Kangaroos, Wallabies, and Rat\u0026ndash;kangaroos. CSIRO Publishing, Collingwood, Australia, pp 99\u0026ndash;108\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDen Boer W (2018) Evolutionary progression of the iconic Australasian kangaroos, rat-kangaroos, and their fossil relatives (Marsupiala: Macropodiformes). Dissertation, Uppsala University\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDen Boer W, Campione NE, Kear BP (2019) Climbing adaptations, locomotory disparity and ecological convergence in ancient stem \u0026lsquo;kangaroos\u0026rsquo;. R Soc Open Sci 6:181617 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1098/rsos.181617\u003c/span\u003e\u003cspan address=\"10.1098/rsos.181617\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDeSantis LRG, Field JH, Wroe S, Dodson JR (2017) Dietary responses of Sahul (Pleistocene Australia-New Guinea) megafauna to climate and environmental change. Paleobiology 43:181\u0026ndash;185 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1017/pab.2016.50\u003c/span\u003e\u003cspan address=\"10.1017/pab.2016.50\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDunn RH (2018) Functional morphology of the postcranial skeleton. In: Croft DA, Su DF, Simpson SW (eds) Methods in Paleoecology: Reconstructing Cenozoic Terrestrial Environments and Ecological Communities. Springer International Publishing, Cham, pp 23\u0026ndash;36\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEcheverr\u0026iacute;a AI, Becerra F, Vassallo AI (2014) Postnatal ontogeny of limb proportions and functional indices in the subterranean rodent \u003cem\u003eCtenomys talarum\u003c/em\u003e (Rodentia: Ctenomyidae). J Morphol 275:902\u0026ndash;913 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/jmor.20267\u003c/span\u003e\u003cspan address=\"10.1002/jmor.20267\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eElissamburu A, de Santis L (2011) Forelimb proportions and fossorial adaptations in the scratch\u0026ndash;digging rodent \u003cem\u003eCtenomys\u003c/em\u003e (Caviomorpha). J Mammal 92:683\u0026ndash;689 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1644/09-MAMM-A-113.1\u003c/span\u003e\u003cspan address=\"10.1644/09-MAMM-A-113.1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFigueirido B, Mart\u0026iacute;n-Serra A, Janis CM (2016) Ecomorphological determinations in the absence of living analogues: the predatory behavior of the marsupial lion (\u003cem\u003eThylacoleo carnifex\u003c/em\u003e) as revealed by elbow joint morphology. Paleobiology 42:508\u0026ndash;531 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1017/pab.2015.55\u003c/span\u003e\u003cspan address=\"10.1017/pab.2015.55\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFinch M, Freedman L (1988) Functional-morphology of the limbs of \u003cem\u003eThylacoleo carnifex\u003c/em\u003e Owen (Thylacoleonidae, Marsupialia). Aust J Zool 36:251\u0026ndash;272 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1071/ZO9880251\u003c/span\u003e\u003cspan address=\"10.1071/ZO9880251\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFisher RA (1934) Statistical methods for research workers. In: Kots S, Johnson NL (eds) Breakthroughs in Statistics. Springer, New York, pp 66\u0026ndash;70\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFlannery TF (1994) The fossil land mammal record of New Guinea: a review. Sci New Guinea 20:39\u0026ndash;48\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGarland T Jr, Janis CM (1993) Does metatarsal/femur ratio predict maximal running speed in cursorial mammals? J Zool 229:133\u0026ndash;151 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/j.1469-7998.1993.tb02626.x\u003c/span\u003e\u003cspan address=\"10.1111/j.1469-7998.1993.tb02626.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGranatosky MC (2018) A review of locomotor diversity in mammals with analyses exploring the influence of substrate use, body mass and intermembral index in primates. J Zool 306:207\u0026ndash;216 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/jzo.12608\u003c/span\u003e\u003cspan address=\"10.1111/jzo.12608\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHelgen KM, Wells RT, Kear BP, Gerdtz WR, Flannery TF (2006) Ecological and evolutionary significance of sizes of giant extinct kangaroos. Aust J Zool 54:293\u0026ndash;303 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1071/ZO05077\u003c/span\u003e\u003cspan address=\"10.1071/ZO05077\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHildebrand M, Goslow G (1982) Analysis of Vertebrate Structure. Wiley, NJ\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIBM Corp (2019) IBM SPSS Statistics for Macintosh, Version 260. Armonk, NY\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJanis CM, Wilhelm PB (1993) Were there mammalian pursuit predators in the Tertiary? Dances with wolf avatars. J Mamm Evol 1:103\u0026ndash;125 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/BF01041590\u003c/span\u003e\u003cspan address=\"10.1007/BF01041590\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJanis CM, Buttrill K, Figueirido B (2014) Locomotion in extinct giant kangaroos: were sthenurines hop-less monsters? PLoS One 9:e109888 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1371/journal.pone.0109888\u003c/span\u003e\u003cspan address=\"10.1371/journal.pone.0109888\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJanis CM, Napoli JG, Billingham C, Mart\u0026iacute;n-Serra A (2020) Proximal humerus morphology indicates divergent patterns of locomotion in extinct giant kangaroos. J Mammal Evol 27:627\u0026ndash;647 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s10914-019-09494-5\u003c/span\u003e\u003cspan address=\"10.1007/s10914-019-09494-5\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJanis CM, O\u0026rsquo;Driscoll AM, Kear BP (2023) Myth of the QANTAS leap: perspectives on the evolution of kangaroo locomotion. Alcheringa 47:671\u0026ndash;685 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/03115518.2023.2195895\u003c/span\u003e\u003cspan address=\"10.1080/03115518.2023.2195895\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJones B (2020) Locomotor divergence in Macropodoidea: \u003cem\u003eProtemnodon\u003c/em\u003e was not a giant hopping kangaroo. Masters\u0026rsquo; thesis, University of Bristol, Bristol\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJones B, Mart\u0026iacute;n-Serra A, Rayfield EJ, Janis CM (2022) Distal humeral morphology indicates locomotory divergence in extinct giant kangaroos. J Mammal Evol 29:27\u0026ndash;41 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s10914-021-09576-3\u003c/span\u003e\u003cspan address=\"10.1007/s10914-021-09576-3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKear BP, Lee MSY, Gerdtz WR, Flannery TF (2008) Evolution of hind limb proportions in kangaroos (Marsupalia: Macropodoidea). In: Sargis EF, Dagosto M (eds) Mammalian Evolutionary Morphology: A Tribute to Frederick S. Szalay. Springer, New York, pp 25\u0026ndash;55\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKerr IA, Prideaux GJ (2022) A new genus of kangaroo (Marsupialia, Macropodidae) from the late Pleistocene of Papua New Guinea. T Roy Soc South Aust 146:295\u0026ndash;318 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/03721426.2022.2086518\u003c/span\u003e\u003cspan address=\"10.1080/03721426.2022.2086518\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKruskal WH, Wallis WA (1952) Use of ranks in one\u0026ndash;criterion variance analysis. J Am Stat Assoc 47:583\u0026ndash;621 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/01621459.1952.10483441\u003c/span\u003e\u003cspan address=\"10.1080/01621459.1952.10483441\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLlamas B, Brotherton P, Mitchell KJ, Templeton JEL, Thomson VA, Metcalf JL, Armstrong KN, Kasper M, Richards SM, Camens AB, Lee MSY, Cooper A (2015) Late Pleistocene Australian marsupial DNA clarifies the affinities of extinct megafaunal kangaroos and wallabies. Mol Biol Evol 32:574\u0026ndash;584 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1093/molbev/msu338\u003c/span\u003e\u003cspan address=\"10.1093/molbev/msu338\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eL\u0026ecirc; S, Josse J, Husson F (2008) FactoMineR: an R package for multivariate analysis. J Stat Softw 25:1\u0026ndash;18 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.18637/jss.v025.i01\u003c/span\u003e\u003cspan address=\"10.18637/jss.v025.i01\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMcGowan CP, Skinner J, Biewener AA (2008) Hind limb scaling of kangaroos and wallabies (superfamily Macropodoidea): implications for hopping performance, safety factor, and elastic scaling. J Anat 212:153\u0026ndash;163 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/j.1469-7580.2007.00841.x\u003c/span\u003e\u003cspan address=\"10.1111/j.1469-7580.2007.00841.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMeachen\u0026ndash;Samuels J (2012) Morphological convergence of the prey\u0026ndash;killing arsenal of sabretooth predators. Paleobiology 38:1\u0026ndash;14 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1666/10036.1\u003c/span\u003e\u003cspan address=\"10.1666/10036.1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMeachen-Samuels J, Van Valkenburgh B (2009) Forelimb indicators of prey-size preference in the Felidae. J Morphol 270:729\u0026ndash;744 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/jmor.10712\u003c/span\u003e\u003cspan address=\"10.1002/jmor.10712\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMoore L (2008) Functional morphology and palaeoecology of extinct macropodoids, sthenurines and \u003cem\u003eProtemnodon\u003c/em\u003e spp (Marsupialia; Diprotodontia) BSc thesis, Flinders University, South Australia\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePolly PD (2020) Ecometrics and Neogene faunal turnover: the roles of cats and hindlimb morphology in the assembly of carnivoran communities in the New World. Geodiversitas 42:257\u0026ndash;304 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.5252/geodiversitas2020v42a17\u003c/span\u003e\u003cspan address=\"10.5252/geodiversitas2020v42a17\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRichards H, Grueter C, Milne N (2015) Strong arm tactics: sexual dimorphism in macropodid limb proportions. J Zool 297:123\u0026ndash;131 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/jzo.12264\u003c/span\u003e\u003cspan address=\"10.1111/jzo.12264\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRodman PS (1979) Skeletal differentiation of \u003cem\u003eMacaca fascicularis\u003c/em\u003e and \u003cem\u003eMacaca nemestrina\u003c/em\u003e in relation to arboreal and terrestrial quadrupedalism. Am J Phys Anthropol 51:51\u0026ndash;62 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/ajpa.1330510107\u003c/span\u003e\u003cspan address=\"10.1002/ajpa.1330510107\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRSTUDIO Team (2015) RStudio: Integrated Development for R RStudio, Inc. Boston, MA. Available on: http://wwwrstudiocom/\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSamuels JX, Van Valkenburgh B (2008) Skeletal indicators of locomotor adaptations in living and extinct rodents. J Morphol 269:1387\u0026ndash;1411 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/jmor.10662\u003c/span\u003e\u003cspan address=\"10.1002/jmor.10662\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSamuels JX, Meachen JA, Sakai SA (2013) Postcranial morphology and the locomotor habits of living and extinct carnivorans. J Morphol 274:121\u0026ndash;146 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/jmor.20077\u003c/span\u003e\u003cspan address=\"10.1002/jmor.20077\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSchneider CA, Rasband WS, Eliceiri KW (2012) NIH Image to ImageJ: 25 years of image analysis. Nat Methods 9:671\u0026ndash;675 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1038/nmeth.2089\u003c/span\u003e\u003cspan address=\"10.1038/nmeth.2089\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSeebeck JH, rose RW (1989) Potoroidae 1989. In: Walton DW, Richardson, BJ (eds) Fauna of Australia: Mammalia. Surrey Beatty, Sydney, pp. 716\u0026ndash;739\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShapiro SS, Wilk MB (1965) An analysis of variance test for normality (complete samples). Biometrika 52:591\u0026ndash;611 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.2307/2333709\u003c/span\u003e\u003cspan address=\"10.2307/2333709\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShockey BJ, Croft DA, Anaya F (2007) Analysis of function in the absence of extant functional homologues: a case study using mesotheriid notoungulates (Mammalia). Paleobiology 33:227\u0026ndash;247 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1666/05052.1\u003c/span\u003e\u003cspan address=\"10.1666/05052.1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSmirnov NV (1939) Estimate of deviation between empirical distribution functions in two independent samples. Bull Mosc Univ 2:3\u0026ndash;16\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSnelling EP, Biewener AA, Hu Q, Taggart DA, Fuller A, Mitchell D, Maloney SK, Seymour RS (2017) Scaling of the ankle extensor muscle-tendon units and the biomechanical implications for bipedal hopping locomotion in the post-pouch kangaroo \u003cem\u003eMacropus fuliginousus\u003c/em\u003e. J Anat 231:921\u0026ndash;930 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/joa.12715\u003c/span\u003e\u003cspan address=\"10.1111/joa.12715\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTedford RH (1966) A review of the macropodid genus \u003cem\u003eSthenurus\u003c/em\u003e. Univ of Calif Publ in Geol Sci 64:1\u0026ndash;165\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVan Valkenburgh B (1987) Skeletal indicators of locomotor behavior in living and extinct carnivores. J Vertebr Paleontol 7:162\u0026ndash;182 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/02724634.1987.10011651\u003c/span\u003e\u003cspan address=\"10.1080/02724634.1987.10011651\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWagstaffe, AY (2018) The biomechanics of kangaroo feet: hopping for a better resolution. Masters\u0026rsquo; thesis, University of Bristol, UK\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWagstaffe AY, Kunz C, O'Driscoll AM, Janis CM, Rayfield EJ (2022) Divergent locomotion in \u0026ldquo;giant\u0026rdquo; kangaroos: Evidence from foot bone bending resistance and microanatomy. J Morphol 283:313\u0026ndash;332 doi:\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/jmor.21445\u003c/span\u003e\u003cspan address=\"10.1002/jmor.21445\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWarburton NM, Prideaux GJ (2010) Functional pedal morphology of the extinct tree-kangaroo \u003cem\u003eBohra\u003c/em\u003e (Diprotodontia: Macropodidae). In: Coulson G, Eldridge MDB (eds) Macropods: The Biology of Kangaroos, Wallabies, and Rat\u0026ndash;kangaroos. CSIRO Publishing, Collingwood, Australia, pp 137\u0026ndash;151\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWarburton NM, Prideaux GJ (2021) The skeleton of \u003cem\u003eCongruus kitcheneri\u003c/em\u003e, a semiarboreal kangaroo from the Pleistocene of southern Australia. R Soc Open Sci 8:202216. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1098/rsos.202216\u003c/span\u003e\u003cspan address=\"10.1098/rsos.202216\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWells RT, Tedford RH (1995) \u003cem\u003eSthenurus\u003c/em\u003e (Macropodidae, Marsupialia) from the Pleistocene of Lake Callabonna, South Australia. Bull Am Mus Nat Hist 225:1\u0026ndash;111\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWesterman M, Loke S, Tan MH, Kear BP (2022) Mitogenome of the extinct Desert \u0026lsquo;rat-kangaroo\u0026rsquo; times the adaptation to aridity in macropodoids. Sci Rep 12:5829 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1038/s41518-022-09568-0\u003c/span\u003e\u003cspan address=\"10.1038/s41518-022-09568-0\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWindsor D, Dagg A (1971) The gaits of the Macropodinae (Marsupialia). J Zool 163:165\u0026ndash;175 \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/j.1469-7998.1971.tb04530.x\u003c/span\u003e\u003cspan address=\"10.1111/j.1469-7998.1971.tb04530.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-mammalian-evolution","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jomm","sideBox":"Learn more about [Journal of Mammalian Evolution](http://link.springer.com/journal/10914)","snPcode":"10914","submissionUrl":"https://submission.nature.com/new-submission/10914/3","title":"Journal of Mammalian Evolution","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Macropodoidea, Protemnodon, Biomechanics, Locomotion","lastPublishedDoi":"10.21203/rs.3.rs-4006700/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4006700/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eKangaroos (Macropodoidea) display a diversity of locomotor modes, from bounding quadrupedally to hopping bipedally, but hopping has a body mass limit, which was exceeded by a number of extinct taxa. In the Pleistocene a variety of \"giant\u0026rdquo; kangaroos existed: members of the extinct subfamily Sthenurinae have been previously considered to have a type of locomotion different from extant kangaroos (bipedal striding), but the primary locomotor mode of the large species of the extinct \"giant\" genus \u003cem\u003eProtemnodon\u003c/em\u003e, closely related to extant large kangaroos, has undergone little question. Here, the association between limb proportions and locomotor mode across Macropodoidea is assessed by examination of functional limb indices. We show that large (\u0026gt;\u0026thinsp;100 kg) \u003cem\u003eProtemnodon\u003c/em\u003e species are unlike any other known macropodoids; their position in this functional morphospace, along with other evidence on humeral morphology, supports prior hypotheses of a primarily quadrupedal mode of locomotion, likely some sort of bounding.\u003c/p\u003e","manuscriptTitle":"Hop, Walk or Bound? Limb Proportions in Kangaroos and the Probable Locomotion of the extinct genus Protemnodon","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-06 05:50:52","doi":"10.21203/rs.3.rs-4006700/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-04-11T11:50:41+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-03-22T15:38:33+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"11858d0f-2642-42b9-a0b8-a33c734ef1bd","date":"2024-03-15T14:23:47+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-03-08T16:34:19+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-03-04T00:25:37+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-03-04T00:25:37+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Mammalian Evolution","date":"2024-03-02T14:02:58+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-mammalian-evolution","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jomm","sideBox":"Learn more about [Journal of Mammalian Evolution](http://link.springer.com/journal/10914)","snPcode":"10914","submissionUrl":"https://submission.nature.com/new-submission/10914/3","title":"Journal of Mammalian Evolution","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"4c25ea9b-091e-478b-8748-65860a2a15c7","owner":[],"postedDate":"March 6th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-07-09T05:17:33+00:00","versionOfRecord":{"articleIdentity":"rs-4006700","link":"https://doi.org/10.1007/s10914-024-09725-4","journal":{"identity":"journal-of-mammalian-evolution","isVorOnly":false,"title":"Journal of Mammalian Evolution"},"publishedOn":"2024-06-01 05:17:33","publishedOnDateReadable":"June 1st, 2024"},"versionCreatedAt":"2024-03-06 05:50:52","video":"","vorDoi":"10.1007/s10914-024-09725-4","vorDoiUrl":"https://doi.org/10.1007/s10914-024-09725-4","workflowStages":[]},"version":"v1","identity":"rs-4006700","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4006700","identity":"rs-4006700","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}