Trophic relationships among Lujanian mammals 30 years later: brief review and the example of the Arroyo del Vizcaíno Local Fauna

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Fariña This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7363866/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 16 Feb, 2026 Read the published version in Evolutionary Ecology → Version 1 posted 11 You are reading this latest preprint version Abstract The structure of trophic interactions in extinct communities is a key aspect of palaeoecological reconstruction. Three decades after its initial publication, the thermodynamic model proposed for the Lujanian (late Pleistocene–early Holocene) South American megafauna is revisited here, considering its legacy, criticisms, and further developments. The model, based on Damuth’s inverse relationship between body mass and population density, had suggested an energetic imbalance in the classical Luján Local Fauna: insufficient primary productivity for herbivores and an apparent excess of prey biomass for carnivores. Some criticisms focused on assumptions regarding metabolic rates and diet composition. We assess these concerns in light of new evidence and apply the model to the Arroyo del Vizcaíno Local Fauna (AdV, Uruguay), a rich and minimally time-averaged assemblage of Lujanian megafauna. Updated estimates of body mass, population density, and energetic requirements confirm the previous imbalance pattern, suggesting that some taxa. especially among ground sloths, may have included significant animal matter in their diet. A sensitivity analysis varying the field metabolic rate and assimilation efficiency shows that this pattern is robust across a biologically plausible parameter space. Although uncertainties remain, particularly regarding digestive physiology and local productivity, the results underscore the value of thermodynamic constraints for understanding extinct ecosystems. This integrative approach offers a testable framework to explore community structure and the ecological roles of now-extinct taxa in megafaunal systems worldwide. South American megafauna Trophic networks Thermodynamic models Late Pleistocene Ground sloths Arroyo del Vizcaíno Sensitivity analysis Figures Figure 1 Introduction Three decades ago, I finished my PhD thesis and started publishing ideas that were received with controversy, an always welcome outcome in the collective endeavour of creating science. My most cited only author paper (Fariña 1996 , published in the now extinct journal Evolutionary Theory) is an example of the interest given since then to the studies of the South American megafauna palaeobiology, its composition, the habits of its species, their palaeoecology and also their demise in geologically very recent times (Fariña et al. 2013 ; Fariña & Vizcaíno 2024 ). Using a trophic thermodynamical approach based on the formidable finding by John Damuth ( 1981 ) about the variation of population density with body mass, I claimed that the Luján local fauna, the one that gives its name to the latest Pleistocene South American Land Mammal Age (SALMA) and Stage/Age (Cione & Tonni 1999 ), was not balanced in regard to the amount of available plant food for its herbivores as well as it had an excess of animal food offered to the carnivorous trophic level, an analysis that led me to the conclusion that possibly some of the traditionally considered herbivores could have had a more diverse diet. Given their strange morphology and at body sizes that renders comparison with their modern relatives so difficult, the giant sloths were the main suspects to have been those meat eaters in disguise. My intellectual solo effort pride and joy, Fariña’s ( 1996 ) study on trophic classification in South American Quaternary mammals has proven an important source of inspiration for a wide range of palaeoecological and evolutionary analyses that cited it. Citation metrics from databases such as Google Scholar underscore its continued impact across such disciplines as palaeontology, ecology and functional morphology. Although citation frequency can vary over time, the following representative studies authored by scholars other than myself exemplify the methodological and conceptual influence of that work. Apart from further developments and applications of the model, as well as source of clues for interpreting food habits in Xenarthrans by my own team and other closely related research groups (Fariña & Blanco 1996 ; Palmqvist et al. 2003 ; Vizcaino et al. 2006; Fariña et al. 2014 ; Di Giacomo & Fariña, 2017 ; to cite only a few) and references in general publications on the South American megafauna (Fariña et al. 2013 ; Fariña & Vizcaíno 2024 ), the model was considered and applied (e.g. Saarinen 2019 ) or new ones were created that found their source in that paper, including in other regions (Brazil: Donatti et al. 2007 ; Australia: Wroe et al. 2004 ; United States. France et al. 2007 ; Europe: Palmqvist et al. 2003 , Rodríguez-Gómez et al. 2024 and references therein) and ages such as Miocene (Rodríguez-Gómez et al. 2020) and Middle Pleistocene (Domingo et al. 2017 ). Stepping ahead of that model, Pires et al. ( 2015 ) demonstrated how megafauna interaction networks became more vulnerable following the arrival of modern humans on the continent, while Segura et al. ( 2016 ) found that the structure of Pleistocene food webs resembled that of modern faunas, despite the exceptional body sizes of many taxa. Finally, there are also cases of publications that hardly agree (if at all) with the views I expressed there, such as Prevosti & Vizcaíno ( 2006 ), Prevosti & Forasiepi ( 2009 , 2018) and Bocherens et al. 2016 , 2017 (for discussion, see Varela & Fariña 2018; Bocherens et al. 2018 ). Among other possible weaknesses, the problem of time-averaging is an always likely possibility that inferences made on a fossil site or fauna could be rendered invalid due to the species represented could have lived in different times. To address that, the richly fossiliferous Arroyo del Vizcaíno site (hereafter AdV, Fariña et al. 2014b ) was chosen. It consists of a finding that has provided remains of 16 species of mammals belonging to the Lujanian Land Mammal Age (late Pleistocene-early Holocene), especially of the impressive South American megafauna (Fariña et al. 2013 ). With a chronology of over 33 cal kybp (Fariña et al. 2022 ), it must have been formed at the very end of the MIS 3 (Lisiecki & Raymo, 2005 ; Kleman et al. 2021 ) and, according to the rather gentle topography and the consequent form of the remain-providing region of only a few tens of square kilometres, the individuals represented must have lived in the neighbouring areas during a time span of only a few centuries at most (see radiocarbon dates in Fariña et al. 2014b ; Baleka et al. 2022 ; Fariña et al. 2022 ), so yielding a good example of a geologically very moderate time-averaging while spanning through a long enough ecological time to have sampled the biota of that time and place. Material and Methods Body mass and diet All species identified within the AdV site and listed above were categorised based on their inferred dietary preferences. Body mass estimates for Lestodon armatus , Glossotherium robustum , Glyptodon reticulatus , Doedicurus clavicaudatus , Panochthus tuberculatus , Toxodon platensis , Notiomastodon platensis and Smilodon populator were sourced from the means in Fariña et al. ( 1998 ) rounded to the next hundred. In the case of Mylodon darwinii , the figure given by Christiansen & Fariña ( 2001 ) was taken. Valgipes bucklandi was discussed to have had a significant variation in size, as summed up by Lobato et al. ( 2021 ), but the dimensions of the tibiofibula there described is compatible with a scelidotherine of about 700 kg. The remaining sloth found, Nothrotheriops sp., was estimated by Varela et al. ( 2023 ) as falling withing the size range of Nothrotheriops shastense (McDonald 2005 ). The two horse species found have been identified as Hippidion principale and Equus (Amerhippus) neogeus (Varela et al. 2023 ), the estimates for them were rounded from Alberdi et al. ( 1995 ). In the case of the cervids, the calcaneus CAV 432 (Cervidae indet. sp. 1) is of a size similar to that of Antifer ultra and hence the estimation for this species will be used (Cassini et al. 2016 ), while the dimensions of the humerus CAV 576 (Cervidae indet. sp. 2) yield an average of about 80 kg using Scott’s ( 1990 ) equations H1, H1', H3, H4, H5, H7 and H8, so that value will be used. At 236 mm in length, the metapodial CAV 1465 has dimensions and robustness compatible with Hemiauchenia paradoxa or, less likely, La ma guanicoe , but its length yields estimates of circa 130 kg when the appropriate equations in Scott ( 1990 ) are used. Population density Population densities for each herbivorous taxon were estimated using the general equation proposed by Damuth ( 1981 ): log D = -0.75 log m + 4.23, where D represents population density in individuals per square kilometre, and m denotes body mass in grams. This equation is empirical, derived from a broad survey of modern ecosystems. The standard error of the slope is 0.026; applying a slope one standard error lower than − 0.75 does not significantly affect the overall outcomes. Mass specific metabolic rates for herbivores were computed using the equation presented by Peters ( 1983 ): log R = -0.25 log m + 0.6128, where R denotes the mass-specific metabolic rate (in J kg⁻¹ s⁻¹) and m the body mass in grams. The validity of this formulation, originally derived from Kleiber's (1932) work, was challenged by Packard and Birchard ( 2008 ), who identified a mathematical artefact that leads to an overestimation of metabolic rates in large mammals. A revised formulation was later proposed by McNab ( 2008 ), representing a significant effort to improve the modelling of metabolic scaling in extant mammals. Fariña et al. ( 2013 ) employed this corrected version in their analysis. Although some change is seen in the results when either model was used, they were not relevant to the conclusions, that remained largely consistent. For the carnivore, population densities were estimated using Damuth’s (1993) equation for African flesh-eaters: log D = -0.64 log m + 2.23, employing the same variables as above. Basal metabolic rates for these Carnivora were calculated using another equation also cited by Peters ( 1983 ): log R = -0.27 log m + 0.6551 Sensitivity analysis To assess the robustness of the trophic model and its assumptions, a univariate sensitivity analysis was conducted. The analysis explored how variations in two key parameters, field metabolic rate (FMR) and assimilation efficiency, affect the total daily energy demand per square kilometre. The body mass of a representative mid-sized megaherbivore (3000 kg) was used, and population density was estimated following Damuth’s relationship, as in the main model. The FMR was varied between 2.0 and 3.0 times the basal metabolic rate (BMR), a range supported by field observations in extant mammals. Assimilation efficiency was varied from 0.4 to 0.6, to reflect dietary and digestive variability across herbivores. The resulting total energetic demands ranged from 356 to 802 MJ m − 2 year − 1 . These values represent a 2.3-fold difference across the tested parameter space, illustrating the significant influence of both physiological and ecological assumptions on overall model output. Importantly, even at the lowest estimated demand, the required productivity remains high relative to known values for grassland ecosystems, thus supporting the conclusion of an energy imbalance independently of exact parameter values. The interaction between FMR and assimilation efficiency also proved non-linear, reinforcing the importance of integrated parameter evaluation in future studies. While a more extensive Monte Carlo analysis could refine these insights, the present sensitivity framework already highlights the resilience of the main conclusions against moderate biological uncertainty. The results are summarised in Fig. 1 and Table 3 . Results The energy demands for each species (Table 1 ) were determined by multiplying its on-crop biomass by its mass-specific metabolic rate. An assimilation efficiency of 50% (based on edible material) was assumed, and the average field rate was considered to be 2.5 times the basal metabolic rate, following Peters ( 1983 ); the results were corrected using McNab’s ( 2008 ) equation as discussed in the M&M section. Summing the energy requirements across all species included in the analysis and converting the resulting values to standard units yields an estimated need of approximately 644 kJ m⁻² year⁻¹ in terms of habitat primary productivity, with the megaherbivores alone accounting for just over 300 kJ m⁻² year⁻¹ of this consumption. Table 1 Herbivorous mammals found in the AdV site, their estimated mass, their calculated on, crop biomass, and their mass, specific basal metabolic rate. Species Mass (kg) On-crop biomass (kg km − 2 ) Basal metabolic rate (J kg − 1 s − ) Lestodon armatus 3400 667 0,42 Glossotherium robustum 1700 561 0,52 Mylodon darwinii 1700 561 0,52 Nothrotheriops sp. 500 413 0,76 Valgipes bucklandi 700 450 0,68 Glyptodon reticulatus 900 535 0,58 Panochthus tuberculatus 1100 562 0,55 Doedicurus clavicaudatus 1500 608 0,50 Toxodon platensis 1600 190 1,11 Hippidion principale 500 142 1,59 Equus (Amerhippus) neogeus 400 134 1,70 Camelidae indet. 130 101 2,40 Cervidae indet. sp. 1 25 67 3,97 Cervidae indet. sp. 2 120 99 2,46 Notiomastodon platensis 7600 687 0,37 Table 2 presents the sole large Carnivoran species identified in the AdV site: the extinct ~ 350 kg sabre-toothed cat Smilodon populator . On-crop biomass was calculated by multiplying its estimated population density by its body mass. The energy requirement of this large carnivore was 2.3 kJ m⁻² year⁻¹ in terms of habitat secondary productivity to sustain basal metabolism, assuming a 50% assimilation efficiency. The secondary productivity of the abovementioned herbivores must have been 16 m⁻² year⁻¹. Table 2 Smilodon populator , species of the order Carnivora found in the AdV site, its estimated mass, its calculated on, crop biomass and its mass, specific basal metabolic rate. See text. Species Mass (kg) On-crop biomass (kg km − 2 ) Basal metabolic rate (J kg − 1 s − 1 ) Smilodon populator 350 11 1.41 Table 3 Sensitivity analysis data Calculated total energy demand per square metre and per year for different combinations of field metabolic rate (FMR) and assimilation efficiency. FMR factor Assimilation efficiency Energy demand (MJ m − 2 year − 1 ) 2.0 0.4 535 2.5 0.4 668 3.0 0.4 802 2.0 0.5 428 2.5 0.5 535 3.0 0.5 641 2.0 0.6 356 2.5 0.6 445 3.0 0.6 535 Discussion It should be highlighted that the metabolic theory of ecology significantly contributed during the last decades in this framework. Mechanisms explaining metabolic scaling were introduced (West et al. 1997 ; Gillolly et al. 2001; Brown et al. 2004) and scaling were widely used for inferring determinants of macroecological patterns (Sibly et al. 2012 ), food web structure (Arim et al. 2007 ; McCann 2012 ), and species size distribution (Brown et al. 1993 ; Marquet et al. 2008 ). The density - body size scaling was a particular focus of attention (Brown et al. 2004; Gillolly et al. 2003; White et al. 2007 ; Arim et al. 2011 ). In local communities, different scalings could be expected due to, among other factors, local interactions, available resources and changes in trophic position with body size. However, at large geographic scales, the − 0.75 represents the main expectation. Primary productivity Recent work on the Río de la Plata Grasslands (RPG), one of largest areas of natural temperate sub-humid grasslands in the world is one of the world's most fertile areas, one of largest areas of natural temperate sub-humid grasslands in the world (Soriano, 1991, Paruelo et al., 2007 ). The most productive natural grasslands currently found in Uruguay reach approximately 8.6 MJ m⁻² year⁻¹ (or 465 g DM m − 2 year − 1 in the Colinas y Lomas del Este; Guido et al. 2014 ) and slightly larger values are given in Paruelo et al. ( 2022 ). According to the model in Fariña ( 1996 ), about 7.5% of this primary productivity would have been required to sustain the herbivore species found, which exceeds the usual 3–6% and equals the extraordinary value obtained for Rwenzori National Park in 1973 (Owen-Smith 1988). Climate and productivity The area in which the site is found had a colder and more arid climate than today at the obtained age, ~ 34 cal kyBP, i.e. during the MIS 3 (Lisiecki & Raymo, 2005 ; Kleman et al. 2021 ). According to current estimates, the mean annual temperatures should have been slightly lower than present and with greater seasonal variability, while the annual precipitation would have been somewhat reduced, estimated at around two-thirds of current figures. However, those estimates should be taken with caution, as there were frequent D-O events (Jouzel et al. 2007 ) that significantly changed those parameters for time lapses in the order of centuries at least. Besides, the high edaphic quality of the region and the presence of periodic floodings of the Palaeoparana river (Sánchez-Saldías & Fariña (2017) must have enhanced primary productivity, it remains unlikely that it might have exceeded by so much the productivity of Uruguay's best natural cattle pastures. It is worth mentioning that the imbalance found in that fauna was proposed to be compensated by the access of the megammals to currently submerged areas, covered by the Atlantic Ocean when the sea level rose at the end of the Pleistocene (Sánchez-Saldías & Fariña 2014). However, Varela & Fariña ( 2025 ) demonstrated that, at least in the case of the giant sloth Lestodon armatus , the home range inferred after the highly localised 87 Sr/ 86 Sr signature suggests relatively limited movement within a defined area, so ruling out the existence of extensive seasonal migrations in this species. Imbalances Fariña ( 1996 ) claimed it is strikingly different from modern analogues that so few large carnivores were found in a local fauna so rich in megaherbivores as Luján. Prevosti & Vizcaíno ( 2006 ) proposed that this paucity should have been compensated by other carnivorous species present in Buenos Aires province, although they did not add other herbivorous species not recorded in that local fauna. Besides, one of those species is the omnivorous ursid Arctotherium tarijense (Figueirido & Soibelzon 2010). In any case, here I present results for an exceptional site, in which some of their critiques are addressed. First, time averaging in the AdV site is very small, with possibly only a few centuries represented (Fariña et al. 2022 ) in the bone accumulation, which cannot be ruled out as a single deposit event. Therefore, this geologically instantaneous formation of the site can be rather safely assumed to accurately portray the biocenosis at its diversity in ecological time. Most importantly, with about 2500 entries in its collection, the extraordinary abundance of fossils found there has yielded remains of otherwise poorly represented species, such as the ground sloths Valgipes bucklandi (Lobato et al. 2021 ) and Nothrotheriops sp. (Varela et al. 2023 ), whose distribution had previously been reported for distant regions of South America. Those occurrences of unexpected taxa imply the high reliance of the AdV site in terms of sampling in its fossilisation process of taxa with a low number of individuals in the source area. Hence, the absence of carnivorans other than the sabre-tooth felid (e.g. canids, ursids or other large felids like puma and jaguar) in this richly fossiliferous assemblage is likely a consequence of their absence in the living community. As discussed in Fariña ( 1996 ), this absence cannot be compensated by small-bodied animalivore hunters or scavengers due to the difficulties in hunting down or processing large prey if their size was not big enough. Additionally, in a site that has yielded a vast number of small bones of the large individuals, no evidence of those medium-sized carnivores has been found. The imbalance found in Fariña et al. (1996) for the Luján Local Fauna is apparent in the AdV site, leaving open the possibility that the ecological role of large-bodied scavengers or opportunistic carnivores remained underutilised or entirely unfilled. From the above, I contended that the Lujanian fauna cannot be well understood using modern ecosystems as a paradigm, which notwithstanding worked very well for the coeval late Pleistocene, mid-latitude Rancho La Brea fauna. To work that double paradox out, i.e. that of the paucity of primary productivity and that the excess of herbivores, I resourced to the logic implicit in Gaston Leroux's (1977) mystery story “Crime in a yellow room”: murders happen in a locked room leading to the conclusion that the culprit must be inside it. Likewise, in Fariña ( 1996 ) it was proposed that the cryptic carnivore must have been disguised among the species so far considered herbivores, leaving the problem of identifying potential candidates. The choice was then the ground sloths, which lack of modern analogues favours the quest for unexpected interpretations of their palaeobiology. That hypothesis was further developed in a study of the arm biomechanics of Megatherium americanum in Fariña & Blanco ( 1996 ), whose olecranon process length was well suited for a rapid extension and a potentially devastating use of its laterally flattened, dagger-like claws. A few years ago, a novel biochemistry procedure was available for identifying the consumption of meat through the relative isotopic values of the aminoacids glutamate and phenylalanine (Tejada et al. 2021 ). It is claimed there that those values alone allow for reliable reconstructions of the trophic positions of both extant and extinct mammals. In that study, Mylodon darwinii value was within the omnivore category, close to that of the American marten Martes americana , although Nothrotheriops lied within the herbivores. Mylodon darwinii is found in the AdV site along with three other close relatives, the mylodontids Lestodon armatus , Glossotherium robustum and Valgipes bucklandi , recently referred to the newly upgraded the family Scelidotheriidae (Tejada et al. 2024 ) that, although split from Mylodontidae, is still closely classified. If all of them were considered omnivores, obtaining their energy from both animal and plant matter, the imbalance is corrected to a large extent: The primary productivity needed to support the herbivores would fall to 9 MJ m⁻² year⁻¹, so closing the gap with a high-quality modern grassland discussed above. Incidentally, the environment of the area in which the AdV site was formed included aquatic plants and also some extension of wooded areas nearby (Martínez-Blanco et al. 2024), which must have enhanced the primary productivity available. It is noteworthy that some of the taxa show isotopic values compatible with the use of closed habitat resources (Varela et al. 2023 ). On the other aspect of the imbalance, if the mylodontid ground sloths obtained a substantial amount of its vital energy from animal matter, the remaining imbalance of the flesh-eating guild needs (6.8 m⁻² year⁻¹) and the secondary productivity (13.8 m⁻² year⁻¹) is only two-fold instead of 7-fold as shown in the Results section. Interestingly, the secondary productivity of the megaherbivores alone (6.0 m⁻² year⁻¹) lies below the flesh-eater energetic needs. The AdV site has also yielded evidence of another species with omnivorous habits: Homo sapiens (Fariña et al. 2014 a). Some of the bones show cut-marks with the features proper of human agency (Fariña 2015 ; Domínguez-Rodrigo et al. 2021) and other lines of evidence are also congruent, such as the mortality profile, the representation of anatomical regions and other bone modifications (Fariña et al. 2025 ). It goes beyond the scope of this paper to assess the rôle of humans if they were present in this community, but their behaviour as an invading species cannot be ruled out, rendering difficult to include us in the model. Conclusions Based on the evidence presented in Fariña ( 1996 ) and the discussion of its implications, a strongly counter-intuitive but plausible hypothesis was then proposed: that some ground sloths were, at least opportunistically, consumers of animal matter. This notion challenged traditional interpretations of their ecology yet found support in the broader energetic and ecological context of the South American Pleistocene megafauna full of giant xenarthrans with no modern analogues to be compared with. The AdV site, with remains that are representative of large and giant mammals living in a rather small area and a during a short period of time, strongly corroborates the views expressed nearly three decades ago. It must be emphasised, however, that the palaeoecology of this remarkable and fauna remains far from fully understood and a highly complex and fascinating issue, especially taking into account the certain possibility that our own species, Homo sapiens , could have been present and added further complexity to the ecological interaction, trophic and otherwise. If this proposal holds valid, then ground sloths would represent the largest terrestrial mammals ever known to have incorporated flesh into their diet, thereby redefining the upper size limits of flesh-eating land vertebrates. Declarations Author Contribution There is only one author. Acknowledgement To the memory of Leigh Van Valen, unorthodox. Matías Arim, Ángeles Beri, Federico Gallego, Anaclara Guido and Luciano Varela made useful suggestions. Data Availability Data is provided within the manuscript and supplementary information files References Alberdi, M. T., & Porter, W. P. (2010). 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Giants beasts updated: A review of new knowledge about the South American megafauna. Journal of Quaternary Science. 39(8): 1139–1153. Fariña RA, Czerwonogora A, Di Giacomo M. 2014. Splendid oddness: the curious palaeoecology of South American Pleistocene mammals revisited. Anais da Academia Brasileira de Ciências 86 (1): 315, 335. Fariña RA, Hayes E, Lemoine LA, Fullagar R, Tambusso PS, Varela L. 2025. An indentation in a 33,000-year-old right calcaneus of the ground sloth Lestodon (Xenarthra, Folivora) from Uruguay and its possible human agency. Swiss Journal of Palaeontology 144: 31. Fariña RA, Tambusso PS, Varela L, Czerwonogora A, Di Giacomo M, Musso M, Bracco, Boksar R, Gascue A. 2014b. Arroyo del Vizcaíno, Uruguay: A fossil, rich 30, ka, old megafaunal locality with cut, marked bones. Proceedings of the Royal Society B 281 (1774): 20132211. Fariña RA, Tambusso PS, Varela L., Gascue, A., & Stafford, T. W. 2022. Hard Facts in an Imperfect Site: The Evidence of Human Presence in the Arroyo del Vizcaíno. Reply to Holcomb et al. PaleoAmerica, 8(4), 307, 314. Fariña RA, Vizcaíno SF, Bargo MS. 1998. Body mass estimations in Lujanian (late Pleistocene-early Holocene of South America) mammal megafauna. Mastozoología Neotropical 5 (2): 87-108. Fariña RA, Vizcaíno SF, De Iuliis G. 2013. Megafauna. Giant Beasts of Pleistocene South America. Bloomington, Indiana University Press, 416 pp. ISBN: 978, 0, 253, 00230, 3. Figueirido B, Soibelzon LH. 2009. Inferring palaeoecology in extinct tremarctine bears (Carnivora, Ursidae) using geometric morphometrics. Lethaia 43: 209–222. France CAM, Zelanko PM, Kaufman AJ, Holtz TR. 2007. Carbon and nitrogen isotopic analysis of Pleistocene mammals from the Saltville Quarry (Virginia, USA): Implications for trophic relationships Palaeogeography, Palaeoclimatology, Palaeoecology 249: 271 – 282 Gillooly JF, Brown JH, West GB, Savage VM, Charnov EL. 2001. Effects of Size and Temperature on Metabolic Rate. Science 293: 2248-2251. Guido A, Díaz Varela R, Baldassini P, Paruelo J. 2014. Spatial and Temporal Variability in Aboveground Net Primary Production of Uruguayan Grasslands. Rangeland Ecology & Management 67: Pages 30-38. Gurovich, B. (2005). Niche partitioning in South American mammals: Evidence from trophic studies. Journal of Mammalian Evolution, 12(3–4), 195–215. Jouzel J, Masson-Delmotte V, Cattani O, Dreyfus G, Falourd S, Hoffmann G, Minster B, Nouet J, Barnola JM, Chappellaz J, Fischer H, Gallet JC, Johnsen S, Leuenberger M, Loulergue L, Luethi D, Oerter H, Parrenin F, Raisbeck G, Raynaud D, Schilt A, Schwander J, Selmo E, Souchez R, Spahni R, Stauffer B, Steffensen JP, Stenni B, Stocker TF, Tison JL, Werner M, Wolff EW. 2007. Orbital and millennial Antarctic climate variability over the past 800,000 years. Science 317: 793-796. Kerber, C., Ribeiro, A. M., & Lopes, R. P. (2003). Reconstruction of Pleistocene trophic networks in southern South America. Journal of South American Earth Sciences, 16(1), 55–70. Kleman J, Hättestrand M, Borgström I, Derek D, Preusser F. 2021. Age and duration of a MIS 3 interstadial in the Fennoscandian Ice Sheet core area – Implications for ice sheet dynamics. Quaternary Science Reviews 264: 107011 Lisiecki, L. E., and M. E. Raymo. 2005. A Pliocene- Pleistocene stack of 57 globally distributed benthic d 18 O records, Paleoceanography 20: PA1003. Lobato C, Varela L, Tambusso PS, Miño-Boilini ÁR, Clavijo L, Fariña RA. 2021. Presence of the ground sloth Valgipes bucklandi (Xenarthra, Folivora, Scelidotheriinae) in southern Uruguay during the Late Pleistocene: Ecological and biogeographical implications. Quaternary International 601 104-115. Lúcena, P., & Marín, G. (2006). Dental microwear and trophic inference in Pleistocene mammals from Argentina. Acta Palaeontologica Polonica, 51(4), 763–776. Marquet, P.A., Abades, S., Keymer, J.E. & Zeballos, H. (2008) Discontinuities in body-size distributions: a view from the top. Discontinuities in ecosystems and other complex systems (eds C.R. Allen & C.S. Holling), pp. 45–57. Columbia University Press, New York. McCann KS. 2012 Food webs. Princeton, NJ: Princeton University Press. McDonald, H. G. 2005. Paleoecology of extinct xenarthrans and the Great American Biotic Interchange. Florida Museum of Natural History, Bulletin 45(4):313-333. McNab, B.K. 2008. An analysis of the factors that influence the level and scaling of mammalian BMR. Comparative Biochemistry and Physiology A 151: 5, 28. Packard G. C., Birchard, G. F. 2008. Traditional allometric analysis fails to provide a valid predictive model for mammalian metabolic rates. Journal of Experimental Biology 211:3581, 3587. Palmqvist P, Gröcke DR, Arribas A, and Fariña RA. 2003. Paleoecological reconstruction of a lower Pleistocene large mammal community using biogeochemical (d 13 C, d 15 N, d 18 O, Sr: Zn) and ecomorphological approaches. Paleobiology, 29(2): 205–229. Paruelo JM, Jobbagy EG, Oesterheld M, Golluscio RA, Aguiar MR. 2007. The grasslands and steppes of Patagonia and the Rio de la Plata. plains”, en Veblen, T., Young, K. y Orme, A. (eds.), The Physical Geography of South America, The Oxford Regional Environments Series, Oxford University Press, Oxford, cap. 14, pp. 232-248. Paruelo, J. M., Oesterheld, M., Altesor, A., Piñeiro, G., Rodríguez Fábregas, C., Baldassini, P., Irisarri, G., López-Mársico, L., Pillar, V. D. 2022. Grazers and fires: Their role in shaping the structure and functioning of the Río de la Plata Grasslands. Ecología Austral 32: 784-805. Peters, R. H. 1983. The ecological implications of body size. Cambridge University Press, Cambridge, 329 pp. Pires, M.M., Koch, P.L., Fariña, R.A., de Aguiar, M.A., dos Reis, S.F., Guimarães Jr., P.R., 2015. Pleistocene megafaunal interaction networks became more vulnerable after human arrival. Proc. Biol. Sci. 282 (1814), 20151367. Prevosti, F. J., & Forasiepi, A. M. (2009). Ecological and trophic dynamics of South American mammalian assemblages. Palaeogeography, Palaeoclimatology, Palaeoecology, 273(1–2), 75–84. Prevosti, F.J. and Vizcaíno, S.F. 2006. Paleoecology of the large carnivore guild from the late Pleistocene of Argentina. Acta Palaeontologica Polonica 51 (3): 407–422. Rodríguez Gómez G, Cassini GH, Palmqvist P, Bargo MS, Toledo N, Martín, González JA, Muñoz NA, Kay RF, Vizcaíno SF. 2020. Testing the hypothesis of an impoverished predator guild in the Early Miocene ecosystems of Patagonia: An analysis of meat availability and competition intensity among carnivores. Palaeogeography, Palaeoclimatology, Palaeoecology 554: 109805. Rodríguez Gómez G, Martín, González J. Patrocinio Espigares M, Bermúdez JM. 2024. From meat availability to hominin and carnivore biomass: A paleosynecological approach to reconstructing predator, prey biomass ratios in the Pleistocene. Quaternary Science Reviews 328: 108474 Saarinen J. 2019. The Palaeontology of Browsing and Grazing. in The Ecology of Browsing and Grazing II. 1 edn. Ecological Studies 239: 5, 59. Sánchez, Saldías A, Fariña RA. 2014. Palaeogeographic reconstruction of Minchin palaeolake system, South America: the influence of astronomical forcing. Geoscience Frontiers 5: 249, 259. Savage, V.M., Gillooly, J.F., Brown, J.H., West, G.B. & Charnov, E.L. (2004) Effects of body size and temperature on population growth. American Naturalist, 163, 429–441. Scott, K. 1990. P. Postcranial dimensions of ungulates as predictors of body mass. 301-335. In: Body size in mammalian paleobiology: Estimation and biological implications. (J. Damuth and B.J. MacFadden, eds.). Cambridge University Press, Cambridge, 397 p. Segura, A.M., Fariña, R.A., Arim, M., 2016. Exceptional body sizes but typical trophic structure in a Pleistocene food web. Biol. Lett. 12 (5), 20160228. Sibly, R.M., Brown, J.H. & Kodric-Brown, A. (2012) Metabolic ecology: a scaling approach. Wiley-Blackwell Silva, J. C., & Vizcaíno, S. F. (2004). Late Quaternary extinctions and ecosystem dynamics in South America. Quaternary Research, 61(2), 130–138. Soriano A. 1992. Río de la Plata Grasslands. Ecosystems of the world 8A. Coupland RT (ed.) Natural grasslands. Introduction and Western Hemisphere. Elsevier, Amsterdam. pp. 367–407. Tejada JV, Flynn JJ, MacPhee R, O’Connell TC, Cerling TE, Bermúdez L, Capuñay C, Wallsgrove N, Brian N. Popp BN. 2021. Isotope data from amino acids indicate Darwin’s ground sloth was not an herbivore. Scientific Reports 11:18944. Tejada JV, Antoine P-O, Münch P, Billet G, Hautier L, Delsuc F, Candamine FL. 2024. Bayesian total-evidence dating revisits sloth phylogeny and biogeography: a cautionary tale on morphological clock analyses. Systematic Biology 73: 125-139. Varela L, Fariña RA. 2025. First 87 Sr/ 86 Sr Isotope Data for the Extinct Sloth Lestodon armatus : Insights into the Spatial Ecology of South American Late Pleistocene Megafauna. Proceedings of the Royal Society B 292: 20250309. Varela L, Clavijo L, Tambusso PS, Fariña RA. 2023. A window into a late Pleistocene megafauna community: Stable isotopes show niche partitioning among herbivorous taxa at the Arroyo del Vizcaíno site (Uruguay). Quaternary Science Reviews 317: 108286. Varela, L., Tambusso, P.S., McDonald, H.G. Raúl I. Vezzosi, R.I., Fariña, R.A. 2023. Occurrence of the ground sloth Nothrotheriops (Xenarthra, Folivora) in the Late Pleistocene of Uruguay: new information on its dietary and habitat preferences based on stable isotope analysis. Journal of Mammalian Evolution 30: 561–576. Vizcaíno SF, Bargo MS, Cassini GH 2006. The structure of the fossil mammal communities of the South American Pleistocene Hist Biol. 18(2):105, 115. West GB, Brown JH, Enquist BJ. 1997. A General Model for the Origin of Allometric Scaling Laws in Biology. Science 276: 122-126. White, E.P., Ernest, S.K.M., Kerkhoff, A.J. & Enquist, B.J. (2007) Relationships between body size and abundance in ecology. Trends in Ecology and Evolution, 22, 323–330. Wroe S, Argot C, Dickman C. 2004. On the rarity of big fierce carnivores and primacy of isolation and area: tracking large mammalian carnivore diversity on two isolated continents. Proceedings of the Royal Society London B 271, 1203–1211. Additional Declarations No competing interests reported. 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Fariña","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA4UlEQVRIiWNgGAWjYDCCAyCignQtZxgYeBgYGBuI18LYRooWvuPtFx9XzrsjZ8+/+PmDDwx2croNPGYS+LRInjlTbHh22zNjHolnho0zGJKNzQ4Q0GJwIydNsnHb4cQeiQOGzTwMBxK3EadlzuH6HonjH5v/EKcl/ZhkY8PhBB7+HsNmBmK0AP3CbNhw7LBhzw2ewpk9BkC/HGYrtsCnBRhiDx821ByWZ+8/vuHDjwo7ObPjzRtv4NMCjBADCC2RAHInEDMzsOB1GAMD+wMIzX8ALsT8Ab+WUTAKRsEoGGEAACbmT8vtxN8yAAAAAElFTkSuQmCC","orcid":"","institution":"Universidad de la República","correspondingAuthor":true,"prefix":"","firstName":"Richard","middleName":"A.","lastName":"Fariña","suffix":""}],"badges":[],"createdAt":"2025-08-13 10:23:22","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7363866/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7363866/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10682-026-10387-2","type":"published","date":"2026-02-16T15:59:33+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":90111555,"identity":"1bb9de61-f1fb-4978-8820-b450c38ceae9","added_by":"auto","created_at":"2025-08-28 15:20:27","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":62631,"visible":true,"origin":"","legend":"\u003cp\u003eSensitivity analysis results\u003c/p\u003e\n\u003cp\u003eEffect of varying Field Metabolic Rate (FMR) and assimilation efficiency on total daily energy demand per km² for a 3000 kg herbivore.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7363866/v1/c9432ee35bde9c42870cb5ac.png"},{"id":103251261,"identity":"b1ad833e-14fe-4b09-ba80-fd689f5dd833","added_by":"auto","created_at":"2026-02-23 16:07:33","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":635859,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7363866/v1/600c3d37-0a3a-4f88-ae21-f3b96210e6a5.pdf"},{"id":90112525,"identity":"2fd6eed5-eddf-44da-8ae3-6f2606820828","added_by":"auto","created_at":"2025-08-28 15:28:27","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":30077,"visible":true,"origin":"","legend":"","description":"","filename":"TrophicrelationshipsinAdVSuppMat.docx","url":"https://assets-eu.researchsquare.com/files/rs-7363866/v1/25c79cf4080732899bd9c1bf.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Trophic relationships among Lujanian mammals 30 years later: brief review and the example of the Arroyo del Vizcaíno Local Fauna","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThree decades ago, I finished my PhD thesis and started publishing ideas that were received with controversy, an always welcome outcome in the collective endeavour of creating science. My most cited only author paper (Fari\u0026ntilde;a \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1996\u003c/span\u003e, published in the now extinct journal Evolutionary Theory) is an example of the interest given since then to the studies of the South American megafauna palaeobiology, its composition, the habits of its species, their palaeoecology and also their demise in geologically very recent times (Fari\u0026ntilde;a et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Fari\u0026ntilde;a \u0026amp; Vizca\u0026iacute;no \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Using a trophic thermodynamical approach based on the formidable finding by John Damuth (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e1981\u003c/span\u003e) about the variation of population density with body mass, I claimed that the Luj\u0026aacute;n local fauna, the one that gives its name to the latest Pleistocene South American Land Mammal Age (SALMA) and Stage/Age (Cione \u0026amp; Tonni \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1999\u003c/span\u003e), was not balanced in regard to the amount of available plant food for its herbivores as well as it had an excess of animal food offered to the carnivorous trophic level, an analysis that led me to the conclusion that possibly some of the traditionally considered herbivores could have had a more diverse diet. Given their strange morphology and at body sizes that renders comparison with their modern relatives so difficult, the giant sloths were the main suspects to have been those meat eaters in disguise.\u003c/p\u003e\u003cp\u003eMy intellectual solo effort pride and joy, Fari\u0026ntilde;a\u0026rsquo;s (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1996\u003c/span\u003e) study on trophic classification in South American Quaternary mammals has proven an important source of inspiration for a wide range of palaeoecological and evolutionary analyses that cited it. Citation metrics from databases such as Google Scholar underscore its continued impact across such disciplines as palaeontology, ecology and functional morphology. Although citation frequency can vary over time, the following representative studies authored by scholars other than myself exemplify the methodological and conceptual influence of that work.\u003c/p\u003e\u003cp\u003eApart from further developments and applications of the model, as well as source of clues for interpreting food habits in Xenarthrans by my own team and other closely related research groups (Fari\u0026ntilde;a \u0026amp; Blanco \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1996\u003c/span\u003e; Palmqvist et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Vizcaino et al. 2006; Fari\u0026ntilde;a et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Di Giacomo \u0026amp; Fari\u0026ntilde;a, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; to cite only a few) and references in general publications on the South American megafauna (Fari\u0026ntilde;a et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Fari\u0026ntilde;a \u0026amp; Vizca\u0026iacute;no \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), the model was considered and applied (e.g. Saarinen \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) or new ones were created that found their source in that paper, including in other regions (Brazil: Donatti et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Australia: Wroe et al. \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; United States. France et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Europe: Palmqvist et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2003\u003c/span\u003e, Rodr\u0026iacute;guez-G\u0026oacute;mez et al. 2024 and references therein) and ages such as Miocene (Rodr\u0026iacute;guez-G\u0026oacute;mez et al. 2020) and Middle Pleistocene (Domingo et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Stepping ahead of that model, Pires et al. (\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) demonstrated how megafauna interaction networks became more vulnerable following the arrival of modern humans on the continent, while Segura et al. (\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) found that the structure of Pleistocene food webs resembled that of modern faunas, despite the exceptional body sizes of many taxa. Finally, there are also cases of publications that hardly agree (if at all) with the views I expressed there, such as Prevosti \u0026amp; Vizca\u0026iacute;no (\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2006\u003c/span\u003e), Prevosti \u0026amp; Forasiepi (\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2009\u003c/span\u003e, 2018) and Bocherens et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2016\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2017\u003c/span\u003e (for discussion, see Varela \u0026amp; Fari\u0026ntilde;a 2018; Bocherens et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eAmong other possible weaknesses, the problem of time-averaging is an always likely possibility that inferences made on a fossil site or fauna could be rendered invalid due to the species represented could have lived in different times. To address that, the richly fossiliferous Arroyo del Vizca\u0026iacute;no site (hereafter AdV, Fari\u0026ntilde;a et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2014b\u003c/span\u003e) was chosen. It consists of a finding that has provided remains of 16 species of mammals belonging to the Lujanian Land Mammal Age (late Pleistocene-early Holocene), especially of the impressive South American megafauna (Fari\u0026ntilde;a et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). With a chronology of over 33 cal kybp (Fari\u0026ntilde;a et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), it must have been formed at the very end of the MIS 3 (Lisiecki \u0026amp; Raymo, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Kleman et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) and, according to the rather gentle topography and the consequent form of the remain-providing region of only a few tens of square kilometres, the individuals represented must have lived in the neighbouring areas during a time span of only a few centuries at most (see radiocarbon dates in Fari\u0026ntilde;a et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2014b\u003c/span\u003e; Baleka et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Fari\u0026ntilde;a et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), so yielding a good example of a geologically very moderate time-averaging while spanning through a long enough ecological time to have sampled the biota of that time and place.\u003c/p\u003e"},{"header":"Material and Methods","content":"\u003cp\u003eBody mass and diet\u003c/p\u003e\u003cp\u003eAll species identified within the AdV site and listed above were categorised based on their inferred dietary preferences. Body mass estimates for \u003cem\u003eLestodon armatus\u003c/em\u003e, \u003cem\u003eGlossotherium robustum\u003c/em\u003e, \u003cem\u003eGlyptodon reticulatus\u003c/em\u003e, \u003cem\u003eDoedicurus clavicaudatus\u003c/em\u003e, \u003cem\u003ePanochthus tuberculatus\u003c/em\u003e, \u003cem\u003eToxodon platensis\u003c/em\u003e, \u003cem\u003eNotiomastodon platensis\u003c/em\u003e and \u003cem\u003eSmilodon populator\u003c/em\u003e were sourced from the means in Fari\u0026ntilde;a et al. (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e1998\u003c/span\u003e) rounded to the next hundred. In the case of \u003cem\u003eMylodon darwinii\u003c/em\u003e, the figure given by Christiansen \u0026amp; Fari\u0026ntilde;a (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2001\u003c/span\u003e) was taken. \u003cem\u003eValgipes bucklandi\u003c/em\u003e was discussed to have had a significant variation in size, as summed up by Lobato et al. (\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), but the dimensions of the tibiofibula there described is compatible with a scelidotherine of about 700 kg. The remaining sloth found, \u003cem\u003eNothrotheriops\u003c/em\u003e sp., was estimated by Varela et al. (\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) as falling withing the size range of \u003cem\u003eNothrotheriops shastense\u003c/em\u003e (McDonald \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). The two horse species found have been identified as \u003cem\u003eHippidion principale\u003c/em\u003e and \u003cem\u003eEquus (Amerhippus) neogeus\u003c/em\u003e (Varela et al. \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), the estimates for them were rounded from Alberdi et al. (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1995\u003c/span\u003e). In the case of the cervids, the calcaneus CAV 432 (Cervidae indet. sp. 1) is of a size similar to that of \u003cem\u003eAntifer ultra\u003c/em\u003e and hence the estimation for this species will be used (Cassini et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), while the dimensions of the humerus CAV 576 (Cervidae indet. sp. 2) yield an average of about 80 kg using Scott\u0026rsquo;s (\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e1990\u003c/span\u003e) equations H1, H1', H3, H4, H5, H7 and H8, so that value will be used. At 236 mm in length, the metapodial CAV 1465 has dimensions and robustness compatible with \u003cem\u003eHemiauchenia paradoxa\u003c/em\u003e or, less likely, La\u003cem\u003ema guanicoe\u003c/em\u003e, but its length yields estimates of circa 130 kg when the appropriate equations in Scott (\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e1990\u003c/span\u003e) are used.\u003c/p\u003e\u003cp\u003ePopulation density\u003c/p\u003e\u003cp\u003ePopulation densities for each herbivorous taxon were estimated using the general equation proposed by Damuth (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e1981\u003c/span\u003e):\u003c/p\u003e\u003cp\u003elog \u003cem\u003eD\u003c/em\u003e = -0.75 log \u003cem\u003em\u003c/em\u003e\u0026thinsp;+\u0026thinsp;4.23,\u003c/p\u003e\u003cp\u003ewhere \u003cem\u003eD\u003c/em\u003e represents population density in individuals per square kilometre, and \u003cem\u003em\u003c/em\u003e denotes body mass in grams. This equation is empirical, derived from a broad survey of modern ecosystems. The standard error of the slope is 0.026; applying a slope one standard error lower than \u0026minus;\u0026thinsp;0.75 does not significantly affect the overall outcomes.\u003c/p\u003e\u003cp\u003eMass specific metabolic rates for herbivores were computed using the equation presented by Peters (\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e1983\u003c/span\u003e):\u003c/p\u003e\u003cp\u003elog \u003cem\u003eR\u003c/em\u003e = -0.25 log \u003cem\u003em\u003c/em\u003e\u0026thinsp;+\u0026thinsp;0.6128,\u003c/p\u003e\u003cp\u003ewhere \u003cem\u003eR\u003c/em\u003e denotes the mass-specific metabolic rate (in J kg⁻\u0026sup1; s⁻\u0026sup1;) and m the body mass in grams. The validity of this formulation, originally derived from Kleiber's (1932) work, was challenged by Packard and Birchard (\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), who identified a mathematical artefact that leads to an overestimation of metabolic rates in large mammals. A revised formulation was later proposed by McNab (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), representing a significant effort to improve the modelling of metabolic scaling in extant mammals. Fari\u0026ntilde;a et al. (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) employed this corrected version in their analysis. Although some change is seen in the results when either model was used, they were not relevant to the conclusions, that remained largely consistent.\u003c/p\u003e\u003cp\u003eFor the carnivore, population densities were estimated using Damuth\u0026rsquo;s (1993) equation for African flesh-eaters:\u003c/p\u003e\u003cp\u003elog \u003cem\u003eD\u003c/em\u003e = -0.64 log \u003cem\u003em\u003c/em\u003e\u0026thinsp;+\u0026thinsp;2.23,\u003c/p\u003e\u003cp\u003eemploying the same variables as above. Basal metabolic rates for these Carnivora were calculated using another equation also cited by Peters (\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e1983\u003c/span\u003e):\u003c/p\u003e\u003cp\u003elog \u003cem\u003eR\u003c/em\u003e = -0.27 log \u003cem\u003em\u003c/em\u003e\u0026thinsp;+\u0026thinsp;0.6551\u003c/p\u003e\u003cp\u003eSensitivity analysis\u003c/p\u003e\u003cp\u003eTo assess the robustness of the trophic model and its assumptions, a univariate sensitivity analysis was conducted. The analysis explored how variations in two key parameters, field metabolic rate (FMR) and assimilation efficiency, affect the total daily energy demand per square kilometre. The body mass of a representative mid-sized megaherbivore (3000 kg) was used, and population density was estimated following Damuth\u0026rsquo;s relationship, as in the main model. The FMR was varied between 2.0 and 3.0 times the basal metabolic rate (BMR), a range supported by field observations in extant mammals. Assimilation efficiency was varied from 0.4 to 0.6, to reflect dietary and digestive variability across herbivores. The resulting total energetic demands ranged from 356 to 802 MJ m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e year\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. These values represent a 2.3-fold difference across the tested parameter space, illustrating the significant influence of both physiological and ecological assumptions on overall model output. Importantly, even at the lowest estimated demand, the required productivity remains high relative to known values for grassland ecosystems, thus supporting the conclusion of an energy imbalance independently of exact parameter values. The interaction between FMR and assimilation efficiency also proved non-linear, reinforcing the importance of integrated parameter evaluation in future studies. While a more extensive Monte Carlo analysis could refine these insights, the present sensitivity framework already highlights the resilience of the main conclusions against moderate biological uncertainty. The results are summarised in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eThe energy demands for each species (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e1\u003c/span\u003e) were determined by multiplying its on-crop biomass by its mass-specific metabolic rate. An assimilation efficiency of 50% (based on edible material) was assumed, and the average field rate was considered to be 2.5 times the basal metabolic rate, following Peters (\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e1983\u003c/span\u003e); the results were corrected using McNab\u0026rsquo;s (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) equation as discussed in the M\u0026amp;M section. Summing the energy requirements across all species included in the analysis and converting the resulting values to standard units yields an estimated need of approximately 644 kJ m⁻\u0026sup2; year⁻\u0026sup1; in terms of habitat primary productivity, with the megaherbivores alone accounting for just over 300 kJ m⁻\u0026sup2; year⁻\u0026sup1; of this consumption.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eHerbivorous mammals found in the AdV site, their estimated mass, their calculated on, crop biomass, and their mass, specific basal metabolic rate.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSpecies\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMass (kg)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eOn-crop biomass (kg km\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eBasal metabolic rate (J kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eLestodon armatus\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e3400\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e667\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0,42\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eGlossotherium robustum\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1700\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e561\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0,52\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eMylodon darwinii\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1700\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e561\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0,52\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eNothrotheriops\u003c/em\u003e sp.\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e500\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e413\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0,76\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eValgipes bucklandi\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e700\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e450\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0,68\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eGlyptodon reticulatus\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e900\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e535\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0,58\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003ePanochthus tuberculatus\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e562\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0,55\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eDoedicurus clavicaudatus\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1500\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e608\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0,50\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eToxodon platensis\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1600\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e190\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1,11\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eHippidion principale\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e500\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e142\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1,59\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eEquus (Amerhippus) neogeus\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e400\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e134\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1,70\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCamelidae indet.\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e130\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e101\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2,40\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCervidae indet. sp. 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e67\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e3,97\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCervidae indet. sp. 2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e120\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e99\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2,46\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eNotiomastodon platensis\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e7600\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e687\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0,37\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\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e2\u003c/span\u003e presents the sole large Carnivoran species identified in the AdV site: the extinct\u0026thinsp;~\u0026thinsp;350 kg sabre-toothed cat \u003cem\u003eSmilodon populator\u003c/em\u003e. On-crop biomass was calculated by multiplying its estimated population density by its body mass. The energy requirement of this large carnivore was 2.3 kJ m⁻\u0026sup2; year⁻\u0026sup1; in terms of habitat secondary productivity to sustain basal metabolism, assuming a 50% assimilation efficiency. The secondary productivity of the abovementioned herbivores must have been 16 m⁻\u0026sup2; year⁻\u0026sup1;.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003e\u003cem\u003eSmilodon populator\u003c/em\u003e, species of the order Carnivora found in the AdV site, its estimated mass, its calculated on, crop biomass and its mass, specific basal metabolic rate. See text.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\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\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSpecies\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMass (kg)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eOn-crop biomass\u003c/p\u003e\u003cp\u003e(kg km\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eBasal metabolic rate (J kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eSmilodon populator\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e350\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1.41\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\n\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eSensitivity analysis data Calculated total energy demand per square metre and per year for different combinations of field metabolic rate (FMR) and assimilation efficiency.\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=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFMR factor\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAssimilation efficiency\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eEnergy demand (MJ m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e year\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e535\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e668\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e802\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e428\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e535\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e641\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e356\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e445\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e535\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIt should be highlighted that the metabolic theory of ecology significantly contributed during the last decades in this framework. Mechanisms explaining metabolic scaling were introduced (West et al. \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Gillolly et al. 2001; Brown et al. 2004) and scaling were widely used for inferring determinants of macroecological patterns (Sibly et al. \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), food web structure (Arim et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; McCann \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), and species size distribution (Brown et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e1993\u003c/span\u003e; Marquet et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). The density - body size scaling was a particular focus of attention (Brown et al. 2004; Gillolly et al. 2003; White et al. \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Arim et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). In local communities, different scalings could be expected due to, among other factors, local interactions, available resources and changes in trophic position with body size. However, at large geographic scales, the \u0026minus;\u0026thinsp;0.75 represents the main expectation.\u003c/p\u003e\u003cp\u003ePrimary productivity\u003c/p\u003e\u003cp\u003eRecent work on the R\u0026iacute;o de la Plata Grasslands (RPG), one of largest areas of natural temperate sub-humid grasslands in the world is one of the world's most fertile areas, one of largest areas of natural temperate sub-humid grasslands in the world (Soriano, 1991, Paruelo et al., \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The most productive natural grasslands currently found in Uruguay reach approximately 8.6 MJ m⁻\u0026sup2; year⁻\u0026sup1; (or 465 g DM m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e year\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the Colinas y Lomas del Este; Guido et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) and slightly larger values are given in Paruelo et al. (\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). According to the model in Fari\u0026ntilde;a (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1996\u003c/span\u003e), about 7.5% of this primary productivity would have been required to sustain the herbivore species found, which exceeds the usual 3\u0026ndash;6% and equals the extraordinary value obtained for Rwenzori National Park in 1973 (Owen-Smith 1988).\u003c/p\u003e\u003cp\u003eClimate and productivity\u003c/p\u003e\u003cp\u003eThe area in which the site is found had a colder and more arid climate than today at the obtained age, ~\u0026thinsp;34 cal kyBP, i.e. during the MIS 3 (Lisiecki \u0026amp; Raymo, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Kleman et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). According to current estimates, the mean annual temperatures should have been slightly lower than present and with greater seasonal variability, while the annual precipitation would have been somewhat reduced, estimated at around two-thirds of current figures. However, those estimates should be taken with caution, as there were frequent D-O events (Jouzel et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) that significantly changed those parameters for time lapses in the order of centuries at least. Besides, the high edaphic quality of the region and the presence of periodic floodings of the Palaeoparana river (S\u0026aacute;nchez-Sald\u0026iacute;as \u0026amp; Fari\u0026ntilde;a (2017) must have enhanced primary productivity, it remains unlikely that it might have exceeded by so much the productivity of Uruguay's best natural cattle pastures. It is worth mentioning that the imbalance found in that fauna was proposed to be compensated by the access of the megammals to currently submerged areas, covered by the Atlantic Ocean when the sea level rose at the end of the Pleistocene (S\u0026aacute;nchez-Sald\u0026iacute;as \u0026amp; Fari\u0026ntilde;a 2014). However, Varela \u0026amp; Fari\u0026ntilde;a (\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2025\u003c/span\u003e) demonstrated that, at least in the case of the giant sloth \u003cem\u003eLestodon armatus\u003c/em\u003e, the home range inferred after the highly localised \u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr signature suggests relatively limited movement within a defined area, so ruling out the existence of extensive seasonal migrations in this species.\u003c/p\u003e\u003cp\u003eImbalances\u003c/p\u003e\u003cp\u003eFari\u0026ntilde;a (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1996\u003c/span\u003e) claimed it is strikingly different from modern analogues that so few large carnivores were found in a local fauna so rich in megaherbivores as Luj\u0026aacute;n. Prevosti \u0026amp; Vizca\u0026iacute;no (\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2006\u003c/span\u003e) proposed that this paucity should have been compensated by other carnivorous species present in Buenos Aires province, although they did not add other herbivorous species not recorded in that local fauna. Besides, one of those species is the omnivorous ursid \u003cem\u003eArctotherium tarijense\u003c/em\u003e (Figueirido \u0026amp; Soibelzon 2010). In any case, here I present results for an exceptional site, in which some of their critiques are addressed.\u003c/p\u003e\u003cp\u003eFirst, time averaging in the AdV site is very small, with possibly only a few centuries represented (Fari\u0026ntilde;a et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) in the bone accumulation, which cannot be ruled out as a single deposit event. Therefore, this geologically instantaneous formation of the site can be rather safely assumed to accurately portray the biocenosis at its diversity in ecological time.\u003c/p\u003e\u003cp\u003eMost importantly, with about 2500 entries in its collection, the extraordinary abundance of fossils found there has yielded remains of otherwise poorly represented species, such as the ground sloths \u003cem\u003eValgipes bucklandi\u003c/em\u003e (Lobato et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) and \u003cem\u003eNothrotheriops\u003c/em\u003e sp. (Varela et al. \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), whose distribution had previously been reported for distant regions of South America. Those occurrences of unexpected taxa imply the high reliance of the AdV site in terms of sampling in its fossilisation process of taxa with a low number of individuals in the source area. Hence, the absence of carnivorans other than the sabre-tooth felid (e.g. canids, ursids or other large felids like puma and jaguar) in this richly fossiliferous assemblage is likely a consequence of their absence in the living community.\u003c/p\u003e\u003cp\u003eAs discussed in Fari\u0026ntilde;a (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1996\u003c/span\u003e), this absence cannot be compensated by small-bodied animalivore hunters or scavengers due to the difficulties in hunting down or processing large prey if their size was not big enough. Additionally, in a site that has yielded a vast number of small bones of the large individuals, no evidence of those medium-sized carnivores has been found.\u003c/p\u003e\u003cp\u003eThe imbalance found in Fari\u0026ntilde;a et al. (1996) for the Luj\u0026aacute;n Local Fauna is apparent in the AdV site, leaving open the possibility that the ecological role of large-bodied scavengers or opportunistic carnivores remained underutilised or entirely unfilled. From the above, I contended that the Lujanian fauna cannot be well understood using modern ecosystems as a paradigm, which notwithstanding worked very well for the coeval late Pleistocene, mid-latitude Rancho La Brea fauna.\u003c/p\u003e\u003cp\u003eTo work that double paradox out, i.e. that of the paucity of primary productivity and that the excess of herbivores, I resourced to the logic implicit in Gaston Leroux's (1977) mystery story \u0026ldquo;Crime in a yellow room\u0026rdquo;: murders happen in a locked room leading to the conclusion that the culprit must be inside it. Likewise, in Fari\u0026ntilde;a (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1996\u003c/span\u003e) it was proposed that the cryptic carnivore must have been disguised among the species so far considered herbivores, leaving the problem of identifying potential candidates.\u003c/p\u003e\u003cp\u003eThe choice was then the ground sloths, which lack of modern analogues favours the quest for unexpected interpretations of their palaeobiology. That hypothesis was further developed in a study of the arm biomechanics of \u003cem\u003eMegatherium americanum\u003c/em\u003e in Fari\u0026ntilde;a \u0026amp; Blanco (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1996\u003c/span\u003e), whose olecranon process length was well suited for a rapid extension and a potentially devastating use of its laterally flattened, dagger-like claws. A few years ago, a novel biochemistry procedure was available for identifying the consumption of meat through the relative isotopic values of the aminoacids glutamate and phenylalanine (Tejada et al. \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). It is claimed there that those values alone allow for reliable reconstructions of the trophic positions of both extant and extinct mammals. In that study, \u003cem\u003eMylodon darwinii\u003c/em\u003e value was within the omnivore category, close to that of the American marten \u003cem\u003eMartes americana\u003c/em\u003e, although \u003cem\u003eNothrotheriops\u003c/em\u003e lied within the herbivores.\u003c/p\u003e\u003cp\u003e\u003cem\u003eMylodon darwinii\u003c/em\u003e is found in the AdV site along with three other close relatives, the mylodontids \u003cem\u003eLestodon armatus\u003c/em\u003e, \u003cem\u003eGlossotherium robustum\u003c/em\u003e and \u003cem\u003eValgipes bucklandi\u003c/em\u003e, recently referred to the newly upgraded the family Scelidotheriidae (Tejada et al. \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) that, although split from Mylodontidae, is still closely classified. If all of them were considered omnivores, obtaining their energy from both animal and plant matter, the imbalance is corrected to a large extent: The primary productivity needed to support the herbivores would fall to 9 MJ m⁻\u0026sup2; year⁻\u0026sup1;, so closing the gap with a high-quality modern grassland discussed above. Incidentally, the environment of the area in which the AdV site was formed included aquatic plants and also some extension of wooded areas nearby (Mart\u0026iacute;nez-Blanco et al. 2024), which must have enhanced the primary productivity available. It is noteworthy that some of the taxa show isotopic values compatible with the use of closed habitat resources (Varela et al. \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eOn the other aspect of the imbalance, if the mylodontid ground sloths obtained a substantial amount of its vital energy from animal matter, the remaining imbalance of the flesh-eating guild needs (6.8 m⁻\u0026sup2; year⁻\u0026sup1;) and the secondary productivity (13.8 m⁻\u0026sup2; year⁻\u0026sup1;) is only two-fold instead of 7-fold as shown in the Results section. Interestingly, the secondary productivity of the megaherbivores alone (6.0 m⁻\u0026sup2; year⁻\u0026sup1;) lies below the flesh-eater energetic needs.\u003c/p\u003e\u003cp\u003eThe AdV site has also yielded evidence of another species with omnivorous habits: \u003cem\u003eHomo sapiens\u003c/em\u003e (Fari\u0026ntilde;a et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2014\u003c/span\u003ea). Some of the bones show cut-marks with the features proper of human agency (Fari\u0026ntilde;a \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Dom\u0026iacute;nguez-Rodrigo et al. 2021) and other lines of evidence are also congruent, such as the mortality profile, the representation of anatomical regions and other bone modifications (Fari\u0026ntilde;a et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). It goes beyond the scope of this paper to assess the r\u0026ocirc;le of humans if they were present in this community, but their behaviour as an invading species cannot be ruled out, rendering difficult to include us in the model.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eBased on the evidence presented in Fari\u0026ntilde;a (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1996\u003c/span\u003e) and the discussion of its implications, a strongly counter-intuitive but plausible hypothesis was then proposed: that some ground sloths were, at least opportunistically, consumers of animal matter. This notion challenged traditional interpretations of their ecology yet found support in the broader energetic and ecological context of the South American Pleistocene megafauna full of giant xenarthrans with no modern analogues to be compared with. The AdV site, with remains that are representative of large and giant mammals living in a rather small area and a during a short period of time, strongly corroborates the views expressed nearly three decades ago.\u003c/p\u003e\u003cp\u003eIt must be emphasised, however, that the palaeoecology of this remarkable and fauna remains far from fully understood and a highly complex and fascinating issue, especially taking into account the certain possibility that our own species, \u003cem\u003eHomo sapiens\u003c/em\u003e, could have been present and added further complexity to the ecological interaction, trophic and otherwise. If this proposal holds valid, then ground sloths would represent the largest terrestrial mammals ever known to have incorporated flesh into their diet, thereby redefining the upper size limits of flesh-eating land vertebrates.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eThere is only one author.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eTo the memory of Leigh Van Valen, unorthodox. Mat\u0026iacute;as Arim, \u0026Aacute;ngeles Beri, Federico Gallego, Anaclara Guido and Luciano Varela made useful suggestions.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eData is provided within the manuscript and supplementary information files\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAlberdi, M. T., \u0026amp; Porter, W. P. (2010). Energetics and foraging strategies of extinct South American fauna. 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Trends in Ecology and Evolution, 22, 323\u0026ndash;330.\u003c/li\u003e\n\u003cli\u003eWroe S, Argot C, Dickman C. 2004. On the rarity of big fierce carnivores and primacy of isolation and area: tracking large mammalian carnivore diversity on two isolated continents. Proceedings of the Royal Society London B 271, 1203\u0026ndash;1211.\u003c/li\u003e\n\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":"evolutionary-ecology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"evec","sideBox":"Learn more about [Evolutionary Ecology](https://www.springer.com/journal/10682)","snPcode":"10682","submissionUrl":"https://submission.nature.com/new-submission/10682/3","title":"Evolutionary Ecology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"South American megafauna, Trophic networks, Thermodynamic models, Late Pleistocene, Ground sloths, Arroyo del Vizcaíno, Sensitivity analysis","lastPublishedDoi":"10.21203/rs.3.rs-7363866/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7363866/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe structure of trophic interactions in extinct communities is a key aspect of palaeoecological reconstruction. Three decades after its initial publication, the thermodynamic model proposed for the Lujanian (late Pleistocene\u0026ndash;early Holocene) South American megafauna is revisited here, considering its legacy, criticisms, and further developments. The model, based on Damuth\u0026rsquo;s inverse relationship between body mass and population density, had suggested an energetic imbalance in the classical Luj\u0026aacute;n Local Fauna: insufficient primary productivity for herbivores and an apparent excess of prey biomass for carnivores. Some criticisms focused on assumptions regarding metabolic rates and diet composition. We assess these concerns in light of new evidence and apply the model to the Arroyo del Vizca\u0026iacute;no Local Fauna (AdV, Uruguay), a rich and minimally time-averaged assemblage of Lujanian megafauna. Updated estimates of body mass, population density, and energetic requirements confirm the previous imbalance pattern, suggesting that some taxa. especially among ground sloths, may have included significant animal matter in their diet. A sensitivity analysis varying the field metabolic rate and assimilation efficiency shows that this pattern is robust across a biologically plausible parameter space. Although uncertainties remain, particularly regarding digestive physiology and local productivity, the results underscore the value of thermodynamic constraints for understanding extinct ecosystems. This integrative approach offers a testable framework to explore community structure and the ecological roles of now-extinct taxa in megafaunal systems worldwide.\u003c/p\u003e","manuscriptTitle":"Trophic relationships among Lujanian mammals 30 years later: brief review and the example of the Arroyo del Vizcaíno Local Fauna","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-28 15:20:23","doi":"10.21203/rs.3.rs-7363866/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-09-19T07:10:12+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-18T19:25:57+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-15T01:54:41+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-12T11:06:30+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"27271126069628901874356663604800705737","date":"2025-09-04T20:03:25+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"50914159776863999316616850994450627126","date":"2025-09-01T12:26:51+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"9894315239661596742530778958941986780","date":"2025-08-20T12:13:42+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-20T09:52:42+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-08-14T07:49:18+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-08-14T07:47:54+00:00","index":"","fulltext":""},{"type":"submitted","content":"Evolutionary Ecology","date":"2025-08-13T10:17:13+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"evolutionary-ecology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"evec","sideBox":"Learn more about [Evolutionary Ecology](https://www.springer.com/journal/10682)","snPcode":"10682","submissionUrl":"https://submission.nature.com/new-submission/10682/3","title":"Evolutionary Ecology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"3a60b17f-a628-40f8-902e-5a275097d454","owner":[],"postedDate":"August 28th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-02-23T16:04:44+00:00","versionOfRecord":{"articleIdentity":"rs-7363866","link":"https://doi.org/10.1007/s10682-026-10387-2","journal":{"identity":"evolutionary-ecology","isVorOnly":false,"title":"Evolutionary Ecology"},"publishedOn":"2026-02-16 15:59:33","publishedOnDateReadable":"February 16th, 2026"},"versionCreatedAt":"2025-08-28 15:20:23","video":"","vorDoi":"10.1007/s10682-026-10387-2","vorDoiUrl":"https://doi.org/10.1007/s10682-026-10387-2","workflowStages":[]},"version":"v1","identity":"rs-7363866","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7363866","identity":"rs-7363866","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}