Hypoflexid function in the “trenchant heel” of carnassial teeth, with comments on talonid evolution

Hypoflexid function in the “trenchant heel” of carnassial teeth, with comments on talonid evolution | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Hypoflexid function in the “trenchant heel” of carnassial teeth, with comments on talonid evolution Andreas Lang, Thomas Martin This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4610245/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 09 Sep, 2024 Read the published version in Mammal Research → Version 1 posted 4 You are reading this latest preprint version Abstract The carnassial teeth of Carnivora and Dasyuromorphia are characterized by the enlargement of the carnassial blades and reduction of crushing structures. In some species, the highly carnassialized teeth exhibit a unicuspid talonid with only the hypoconid present (“trenchant heel”). This condition is similar to that seen in the molars of pretribosphenic cladotherians such as Dryolestida, with a single talonid cusp and hypoflexid groove. Tooth wear and reconstruction of the power stroke show that the hypoflexid of the trenchant heel occludes with the paracone of the distal upper antagonist, providing a cutting and guiding function during the power stroke, and maintaining a uniform inclination of the tooth movement up to the point of centric occlusion. In case of the Dasyuromorphia, this occlusal relationship is most pronounced between the distal molars (M4/m4), whereas in the Carnivora it occurs between the upper and lower mesial molars (M1/m1). The occurrence of distal hypoflexid-like grooves is a recurring trend in mammal evolution, before and after the evolution of tribosphenic molars with multicuspid talonid. Carnassials Carnivora Dasyuromorphia Odontology Functional morphology Dental wear Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Carnassial teeth, specialized for the slicing of meat, evolved convergently among carnivorous mammals, i. e. the Carnivora, Hyaenodonta, Oxyaenodonta and Dasyuromorphia (De Muizon & Lange-Badré 1997 ; Van Valkenburgh 2007 , Tarquini et al., 2018). Generally, carnassials are characterized by a secondary reduction of features seen in tribosphenic teeth. Tribosphenic teeth combine the slicing function of the trigonid with the crushing function of the upper molar protocone and the lower molar talonid basin (Crompton & Hiimae 1969; Crompton & Hiimae 1970; Luo et al. 2003). With increasing carnassialization, the protocone of the upper carnassial and the metaconid and talonid cusps (entoconid, hypoconid and hypoconulid) of the lower carnassial are reduced (Lang et al. 2021). This results in a morphology which emphasizes the postvallum/prevallid slicing function and reduces the protocone/talonid crushing function (De Muizon & Lange-Badré 1997 ). The Carnivora are the most diverse extant clade of carnivorous mammals in terms of species and ecomorphology, with the upper P4 and the lower m1 forming the carnassial teeth, while the more distal molars represent the post-carnassial crushing part of the dentition (Van Valkenburgh & Wayne 2010 ). Some extant species of the marsupial Didelphimorphia and Dasyuromorphia also evolved carnassial teeth, with the upper M1-M3 and the lower m2-m4 forming three pairs of carnassials (Tarquini et al. 2018). The distalmost carnassials in marsupials (M3/m4) are the “principal carnassials”, exhibiting the most carnassialized condition of the tooth row (Butler 1946 ; Tarquini et al. 2018; Lang et al. 2021). Generally, the carnassials of carnivorans and marsupials exhibit similar structural modifications, although the upper carnassial blade of carnivorans is between the paracone and the distally displaced metacone, whereas it is between the metacone and the distally displaced metastyle in marsupials (Solé & Ladevèze, 2017 ). The grade of talonid reduction in carnassialized teeth varies between taxa. The carnassials of canids retain a basined talonid which performs a crushing function, although the hypoconulid is reduced in some species such as Canis lupus (Berkovitz & Shellis 2018 ). In the most extreme carnassialized teeth as seen in felids, the talonid is completely absent (Thenius 1989 ). In some species, carnassialization results in a unicuspid talonid which has been termed “trenchant heel” (Wortman & Matthew 1899 ). The trenchant heel is usually interpreted to serve as a secondary cutting feature, with the enlarged single talonid cusp (hypoconid) functioning as an additional cutting blade (Van Valkenburgh 1991 ). Carnassials with a unicuspid trenchant talonid evolved multiple times within the Carnivora. Among extant Caniformia, it is present in Cuon alpinus , Lycaon pictus , and Speothos venaticus (Berkovitz & Shellis 2018 ). Within the Feliformia, it evolved in the extinct Nimravidae (e. g. Nimravus ) (Peigné et al. 2000). In the carnassials of the marsupial Dasyuromorphia, a reduced unicuspid talonid evolved in Sarcophilus harrisii and Thylacinus cynocephalus (Thenius 1989 ). A possible inhibition of the development of certain crown features has been linked to a “structural reversal” of the carnassial crown structure towards the pretribosphenic condition. These structural changes include cusp reduction and a change of the crown topology to a mesio-distal alignment of the remaining cusps, resembling the molariform teeth of the Mesozoic Morganucodonta and Eutriconodonta (Solé & Ladevèze, 2017 ). This inferred resemblance is purely based on morphological similarities, while a functional comparison with carnassial teeth has not been carried out so far. In pretribosphenic molars as seen in dryolestidans, the single talonid cusp and the distal trigonid flank are separated by a deep hypoflexid groove. The groove served as a guiding structure for the upper molar paracone during the power stroke and performed a shearing function with crushing component (Schultz & Martin, 2011 ). In more derived tribosphenic molars, the hypoflexid is reduced and has lost the guiding function. Crushing is instead performed by occlusion of the upper molar protocone into the talonid basin (Schultz & Martin, 2014 ). The observed structural similarities between the unicuspid talonids of carnassial and pretribosphenic teeth (Fig. 1 ) suggest an analogous function. While tooth function of the mammaliaform Morganucodonta relied mostly on puncturing and shearing and less so on precise cutting, eutriconodontans involved all serially arranged cusps into the cutting function, including the distal-most cusp d of the lower molariform (Jäger et al., 2020 ). Cusp d is hypothesized to be the initial talonid cusp, although the homology of the talonid cusps of the tribosphenic molar is debated (Davis 2011 ). There is a structural resemblance between pretribosphenic molars and carnassial teeth with a trenchant heel, both exhibiting a reduced morphology of the tribosphenic condition with multicuspid talonid. This raises the question, if there occurred a functional shift in carnassials with trenchant heel, with a replacement of the protocone/talonid occlusion by a paracone/hypoflexid occlusion, similar to the situation in pretribosphenic molars. The objective of this study is to elucidate the functional role of the hypoflexid groove in carnassial teeth with trenchant heel and in which aspects the trenchant heel is functionally comparable to the distal portion of non-tribosphenic (cusp c + d) and pretribosphenic (cusp d [hypoconulid]) teeth. Methods Nine species with different degrees of carnassialization were studied (list of specimens in Online Resource 1). These include six carnivoran species, with Ichneumia albicauda , Viverra tangalunga and Viverra zibetha representing a weakly carnassialized condition with a tricuspid talonid, Speothos venaticus and Dinictis sp. representing the carnassial condition with a unicuspid trenchant heel and Felis silvestris representing the highly carnassialized condition with a completely reduced talonid. For the marsupials, the dasyuromorph Dasyurus viverrinus represents the weakly carnassialized condition with a tricuspid talonid and Sarcophilus harrisii and Thylacinus cynocephalus represent the condition with a unicuspid trenchant heel, which is the most carnassialized condition among dasyuromorphs. Tooth wear was documented using the digital microscope AXIO Zoom V16 (Zeiss, Oberkochen, Germany). Pictures were generated from image stacks of 20 to 30 focal planes, using the augmented focus depth function of the ZEN pro software (Zeiss). The wear was documented with epoxy resin casts. The Provil ® novo Light regular set (Heraeus Kulzer, Hanau, Germany) was used to create molds of the teeth. It has a high casting accuracy of < 0.1 mm and thus can be used to document microwear on the tooth surface. Casts were made using the RenLam ® M-1 (Huntsman Advanced Materials, Bergkamen, Germany) epoxy resin and the Ren ® HY 956 (Huntsman Advanced Materials) hardener. For coloration of the casts, the Araldite ® DW 0137 Colouring Paste (Huntsman Advanced Materials) was used. Documentation of tooth wear was used to characterize the function of the examined teeth. Occlusal contact between antagonistic teeth results in attrition, which produces polished wear facets on the enamel surface that indicate which crown structures are involved in the occlusal interaction (Butler, 1952 ). Parallel striations on these attritional facets indicate the relative tooth movement (Butler, 1972 ). Mapping of the facets can be used to determine complementary occlusal crown structures and compare the function of different teeth during the power stroke, which is the section of the chewing movement during which occlusal contact occurs (Crompton 1972, Schultz et al., 2017 ). For facets, we use the modular nomenclature of Schultz et al. ( 2017 ), which is based on the topographic position of facets (list of abbreviations in Table 1 ). The teeth were scanned with the v|tome|x s µCT (GE Sensing & Inspection Technologies GmbH phoenix|X-ray, Wunstorf, Germany) of the Bonn Institute of Organismic Biology, Section Paleontology, University of Bonn, Germany. Isotropic scanning resolution varied between 40.9969 µm and 64.017 µm (scanning resolutions are listed in Online Resource 1). The scans of specimens MG Gui Mam 1150 and MG Gui Mam 1155 ( Dryolestes leiriensis ) were provided by Julia Schultz. For comparison to the teeth of Storchodon cingulatus , scans of the specimens NLMH 100023 and NLMH 105654, described in Martin et al. ( 2019 , 2024 ), were used. For segmentation, the software Avizo 8 (Thermo Fisher Scientific, Waltham, MA, USA) was used. For further mesh editing and orientation, the software PolyWorks 2015 IR 13 (InnovMetric Software Inc., Montreal, Quebec, Canada) was used. The Occlusal Fingerprint Analyser (OFA), developed within the DFG Research Unit 771, enables a virtual reconstruction of the power stroke. For the reconstruction, 3D-surface models of antagonistic molars are imported into the software, and are subsequently brought into occlusion via movement in virtual space (Benazzi et al., 2011 ; Kullmer et al., 2009 , 2020 ). The power strokes of two carnivorans ( Viverra tangalunga [Online Resource 2] and Speothos venaticus [Online Resource 3]) and two dasyuromorphs ( Dasyurus viverrinus [Online Resource 4] and Thylacinus cynocephalus [Online Resource 5]) were reconstructed using the OFA software. For the OFA analysis, the carnassials (P4 and m1 of Carnivora, M1-M3 and m2-m4 of Dasyuromorphia) and non-carnassialized posterior teeth (M1 and m2 of Carnivora, M4 of Dasyuromorphia) were used. The 3D model for each single tooth was reduced to a maximum of 50,000 triangles before the analysis using the mesh optimization tool of PolyWorks. Antagonistic tooth rows were positioned in centric occlusion, which is the point of maximum intercuspation sensu Crompton & Hiiemae (1970), using the manual alignment tools of PolyWorks. In tribosphenic teeth, the power stroke is divided into two phases, during the closing and the opening movement of the lower jaw, respectively (Crompton 1971 ). Only the power stroke, when occlusal contacts occur, can reliably be reconstructed with the OFA. The occlusal contacts produce wear facets that can be quantified and that indicate the chewing movements. The directions of the preliminary stroke and the recovery stroke sensu Crompton and Hiiemae (1969) were extrapolated from the movements of the teeth in phase I and phase II (if present). If no phase II is present, a simple orthal jaw opening movement was assumed. The simulation of the chewing stroke with detection of occlusal contacts, direction of movement and inclination of wear facets via OFA analysis was used to analyze the mode of hypoflexid occlusion. The size of the area of occlusal contact per timestep was visualized by contact diagrams. Table 1 List of abbreviations for crown structures, positions of facets and institutions. Abbreviations for crown structures of mammalian molars (modified after Schultz et al. 2017 ) ed Entoconid hd Hypoconid hld Hypoconulid MEC Metacrista ME Metacone md Metaconid MTS Metastyle PACL Paracingulum PA Paracone pa Paraconid PAS Parastyle PR Protocone pr Protoconid Positions of facets b buccal d distal l lingual m mesial Institutional abbreviations HLMD Hessisches Landesmuseum Darmstadt, Germany MG Museu Geológico (Lisbon) of National Laboratory of Energy and Geology of Portugal NLMH Niedersächsisches Landesmuseum Hannover, Germany NMB Naturhistorisches Museum Basel, Switzerland SMF Senckenberg Naturmuseum Frankfurt, Germany SMNK Staatliches Museum für Naturkunde Karlsruhe, Germany ZFMK Zoologisches Forschungsmuseum Alexander Koenig, Bonn, Germany ZMB Museum für Naturkunde, Humboldt-Universität zu Berlin, Germany Results Crown structure of carnivoran and dasyuromorph carnassial teeth The carnassialized teeth of carnivorans and dasyuromorphs are structurally more similar in the lower jaw than in the upper jaw. The lower carnassial teeth are characterized by an enlargement of the paracristid, which forms the V-shaped carnassial blade between the paraconid and the protoconid. On the weakly carnassialized teeth of Ichneumia albicauda , Viverra tangalunga , Viverra zibetha and Dasyurus viverrinus , the hypoconid is the most prominent cusp of the talonid, with the hypoconulid and the entoconid being smaller. In more strongly carnassialized teeth, the metaconid is reduced (as in S. venaticus and Speothos harrisii ) or completely absent (as in Dinictis sp. and Thylacynus cynocephalus ). The only prominent cusp of the talonid is the hypoconid. The upper carnassialized teeth of carnivorans and dasyuromorphs differ in the construction of the carnassial blade. As the blade extends between the metacone and the paracone in carnivorans, the paracone is the only lingual cusp besides the small protocone, which gets reduced in more strongly carnassialized teeth (e.g. F. silvestris ). In contrast to carnivorans, the carnassial blade of dasyuromorphs extends between the metastyle and the metacone, thus the metacone and the paracone are both present as lingual cusps besides the protocone. As in carnivorans, the protocone is reduced in more strongly carnassialized dasyuromorph teeth (as in S. harrisii and T. cynocephalus ). Overall, the metacone is larger than the paracone in dasyuromorph carnassials. On the M4, however, which is the only upper molar lacking a carnassial adaptation, the paracone is larger than the metacone in all studied taxa, as the entire distal portion of the tooth is reduced. While the metacone is part of the carnassial blade on the carnivoran P4, it is smaller than the paracone on the post-carnassial M1, which is lacking a carnassial blade. This pattern is seen in the weakly carnassialized teeth of Ichneumia albicauda , Viverra tangalunga and Viverra zibetha as well as the higher carnassialized teeth of Dinictis sp. and Speothos venaticus . Tooth wear in carnivoran taxa Protocone-talonid-occlusion In the weakly carnassialized teeth of I. albicauda , V. tangalunga and V. zibetha , there are facets on the outer buccal margin of the talonid as well as within the talonid basin. Occlusion of the distal protocone flank of the M1 with the mesial flanks of entoconid and hypoconulid of the m1 is indicated by the presence of facets ed-mb, hld-mb and PR-dl. The mesial flanks of the entoconid and the hypoconulid appear polished in I. albicauda and Viverra spp., indicating attritive wear. Striations running from the apices in cervical direction are only faintly recognizable and point to a mostly orthal movement of the lower jaw during the power stroke. The antagonistic facet PR-dl covers the entire distal protocone flank in some specimens of Viverra spp. In the more carnassialized teeth of Dinictis sp., S. venaticus and F. silvestris , the facets ed-mb, hld-mb, and PR-dl are missing. As the entoconid and hypoconulid are reduced on the lower carnassial of these taxa, antagonistic structures of the talonid for the protocone of the M1 are missing. Protocone-trigonid-occlusion Additionally, the mesial protocone flank of the M1 occludes with the distal trigonid flank of the m1 in the weakly carnassialized teeth of I. albicauda and Viverra spp., indicated by the presence of facets md-d and PR-m. In both Ichneumia and Viverra , the mesial protocone flank extends to the base of the paracone, exhibiting an elongated praeprotocrista that forms a cingulum-like structure. In some specimens, facet PACL-m extends in buccal direction from facet PR-m along the praeprotocrista to the base of the paracone along the paracingulum. Facet md-d forms on the distal metaconid flank, running from the apex of the metaconid along the postprotocristid to the notch of the distal trigonid flank. The metaconid is reduced in size or absent in more carnassialized teeth, resulting in a loss of protocone/metaconid occlusion. Paracone-talonid-occlusion Facet hd-mb forms on the mesial flank of the m1 outer buccal margin of the talonid, where it extends along the praehypocristid. The antagonistic structure that occludes with the praehypocristid is the postparacrista of the P4 paracone, where facet PA-dl is present. On the weakly carnassialized teeth of I. albicauda and Viverra spp., these facets are restricted to the distal paracone flank and the mesial flank of the talonid basin. In the carnassials of Dinictis sp. and S. venaticus , striations show a steep orientation, running with a slight inclination towards buccal on the mesial hypoconid flank and towards lingual on the distal paracone flank (Fig. 2 a, 2 c). In specimens with further progressed wear, facet hd-mb covers the hypoflexid and connects with facet pr-d on the lower molar, and facet PA-dl wraps around the lingual paracone flank, connecting with facet PA-m on the upper molar (Fig. 2 b, 2 d). The inclination of the striations is parallel to the buccal hypoflexid groove. Paracone-trigonid-occlusion Occlusion of the mesial paracone flank of the M1 with the distal trigonid flank of the m1 occurs in all taxa, but a different pattern is observed between weakly and more strongly carnassialized teeth. In I. albicauda and Viverra spp., facet pr-d forms on the lingual side of the distal m1 trigonid flank. The facet is small and covers only a punctiform area, which also applies for the antagonistic facet PA-m. In the more strongly carnassialized carnassials with a unicuspid talonid ( Dinictis sp. and S. venaticus ), facet pr-d covers the entire distal trigonid flank and in some specimens, it extends cervically into the hypoflexid and connects with facet hd-md (Fig. 2 a, 2 c). Occlusion of the mesial paracone flank and the distal trigonid flank appears much more prominent in carnassials with trenchant heel, but it is almost entirely absent in the carnassials of F. silvestris . On the lower carnassials of F. silvestris , only a small punctiform facet pr-d is present on the distal trigonid flank, near the apex of the protoconid. An antagonistic punctiform facet PA-m forms on the small M1, where the paracone is reduced to a small cuspule. Metacone-talonid-occlusion In m1, the distal talonid flank forms a U-shaped crest between the hypoconid and the hypoconulid in Viverra spp. and a V-shaped crest with a small notch in I. albicauda . Along this crest (posthypocristid) extends facet hd-db. A few isolated, weak striations with vertical (cervico-apical) orientation are present. In I. albicauda , facet hd-db remains small, restricted to the vicinity of the hypoconid apex, with more abundant cervico-apical striations. The distal talonid flank occludes with the mesial metacone flank of the M1. Along the praemetacrista, facet ME-ml is developed, which covers the entire mesial metacone flank in some specimens. The metacone is drastically reduced in size on the more carnassialized M1 of Dinictis sp. and S. venaticus . The lack of an attritional facet on the metacone as well as the distal talonid flank points to a loss of occlusal contact of these structures. On the M1 of F. silvestris , the metacone is entirely absent. Tooth wear in dasyuromorph taxa Protocone-talonid-occlusion In the lower molars of D. viverrinus , facets ed-mb and hld-mb, respectively, form on the mesial flanks of the entoconid and the hypoconulid starting from near the apices. With progressing wear, these facets fuse along the entocristid connecting the entoconid with the hypoconulid and finally form a uniform facet running along the inner disto-lingual margin of the talonid basin. The antagonistic upper molar structure that occludes with the entoconid and the hypoconulid is the distal flank of the protocone. Along the postprotocrista stretches facet PR-dl. Facet PR-dl bears steeply inclined unidirectional striations, running from apical in lingual direction. The areas covered by facets ed-mb and hld-mb on the lower molars and facet PR-dl on the upper molars remain relatively small and are restricted to the proximity of the respective cutting crests. This wear has been observed in the talonid basins of m2 and m3, but was not found on m4. In the more carnassialized teeth of S. harrisii and T. cynocephalus , the entoconid and the hypoconulid are reduced and there are no facets indicating occlusion of the talonid with the protocone on any of the lower molars. Protocone-trigonid-occlusion Facet md-d forms on the lingual side of the distal trigonid blade, extending from the tip of the metaconid along the metacristid. It forms on all lower carnassials of D. viverrinus . The striations on facet md-d run steeply from apical to buccal. The antagonistic upper molar structure to occlude with the lingual part of the distal trigonid flank is the mesial flank of the protocone, extending from the praeprotocrista. The upper carnassials of D. viverrinus possess prominent protocones, with facet PR-m forming along the praeprotocrista. On the most distal upper molar of D. viverrinus (M4), facet PR-m is also present on the mesial protocone flank, indicating that the upper M4 with its reduced crown morphology still occludes with the distal trigonid flank of m4. As the metaconid is largely reduced or lost in the carnassials of S. harrisii and T. cynocephalus , there is no antagonistic structure of the trigonid for the protocone to occlude with, resulting in a lack of associated attritional wear. Paracone-talonid-occlusion In D. viverrinus , facet hd-mb forms on the mesial flank of the talonid, where it extends from the praehypocristid and eventually covers the entire mesial flank of the talonid. It is present on all lower carnassial teeth, with striations running steeply inclined from apical to buccal. The antagonistic structure to occlude with the praehypocristid is the postparacrista of the upper molars. Along the postparacrista, facet PA-dl forms on the distal flank of the paracone in D. viverrinus . The striations on facet PA-dl in D. viverrinus are steeply inclined from apical to buccal. On the distalmost lower molar of D. viverrinus (m4), facet hd-mb is also present, indicating occlusion with the distalmost upper molar (M4). In S. harrisii and T. cynocephalus , the prominent hypoflexid of the lower molars is involved into occlusion, where facet hd-mb tends to connect with facet pr-d on the distal trigonid flank with progressing wear. This fusion is most pronounced in the m4 hypoflexid. Facet PA-dl on the upper molars tends to wrap around the lingual paracone flank with progressing wear. Striations cover facets hd-mb and pr-d, which run parallel to the steep hypoflexid inclination and extend into the hypoflexid groove. Paracone-trigonid-occlusion The distal flank of the trigonid on the lower carnassials of D. viverrinus forms a cutting blade along the metacristid, with the latter forming a V-shaped crest between the paraconid and the protoconid. Along the buccal half of this crest, facet pr-d extends along the edge from the apex of the paraconid. In lingual direction, it may connect with facet md-d to form one continuous facet, which can cover the entire distal trigonid flank depending on the progression of wear. The facet is present on all lower carnassials of D. viverrinus , indicating occlusion also with the m4. The antagonistic structure on the upper carnassials is the praeparacrista. Facet PA-m forms along the praeparacrista, covering the mesial flank of the paracone. On the derived carnassials of S. harrisii and T. cynocephalus , the paracone is reduced in size on M2 and M3 and thus the facet on the mesial paracone flank is either bordering the short praeparacrista, as in S. harrisii , or is present as a small, punctiform area, as in T. cynocephalus . On some upper carnassials, a distinctive facet is missing, but unidirectional striations still indicate that attrition may have occurred. The striations on facet PA-m run from apical to lingual, at a steep angle. The reduced crown structure of the upper M4 in dasyuromorphs results in a different wear pattern. The paracone is the most prominent cusp on the M4, with the protocone being reduced in size in D. viverrinus and T. cynocephalus , and absent in S. sarcophilus . Facet PA-m on the M4 covers the entire mesial flank of the paracone in these species, indicating that a cutting function is present during occlusion with the lower distal trigonid flank (Fig. 3 b, 3 d). This is confirmed by the presence of facet pr-d on the m4, which cervically extends from the tip of the protoconid to the distal base of the trigonid, covering the hypoflexid groove (Fig. 3 a, b). With progressing wear, the facet PA-m on M4 extends lingually and wraps around the paracone. This is the result of the hypoflexid moving along the paracone during occlusion. On the m4 of S. harrisii and T. cynocephalus , this leads to the formation of a distinctive polished groove on the buccal talonid flank, with striations formed by attrition in the hypoflexid (Fig. 3 a, b). Metacone-talonid-occlusion Facet hd-db forms on the distal flank of the talonid on the lower carnassials of D. viverrinus , with the exception of m4. It starts forming along the posthypocristid and with progressive wear it extends onto the entire distal talonid flank. The striations on the facet run at a steep inclination from apical to buccal. The posthypocristid occludes with the praemetacrista of the upper molars. Facet ME-ml forms on the mesial flank of the metacone on M2 and M3. On the distalmost upper molar (M4), the metacone is reduced to a vestigial conule, lacking any attritional wear. In S. harrisii and T. cynocephalus , the rather large metacone occludes with the distal talonid flank, resulting in the formation of facets hd-db on the lower molars and ME-ml on the upper molars. These facets form between M2/m2 and M3/m3, but are absent in M4/m4. The smaller paracone occludes with the mesial talonid flank, forming facets hd-mb on the lower molars and PA-dl on the upper molars. Striations are steeply inclined, pointing to a mostly orthal tooth movement. The reduced metacone morphology seen in the ultimate (M4) of the weakly carnassialized molars of D. viverrinus is also present in the ultimate locus (M4) of the more strongly carnassialized molars of S. harrisii and T. cynocephalus . OFA analysis of carnivoran taxa Viverra tangalunga (weakly carnassialized dentition) The viverrid Viverra tangalunga has a weakly carnassialized carnivoran dentition. For the OFA analysis, specimen SMF 697 was chosen. The m1 talonid and the P4 protocone as well as the post-carnassial molars (M1, M2 and m2) are well developed. The complete power stroke comprises 142 timesteps (Fig. 4 a). The initial occlusal contact occurs between the apex of the P4 paracone and the apex of the m1 paraconid, which initiates the first cutting contact between the upper and lower carnassial blades. In timestep 6, a second cutting contact occurs on the lingual side between the apices of the metacone and the protoconid. The occlusal contact between the carnassial blades remains active up until timestep 119. Occlusal contact between the parastyle of M1 and the distal protoconid flank of m1 is also initiated in timestep 6. This area of contact shifts in cervical direction along the distal protoconid flank with further upwards movement of the lower molar and extends into the hypoflexid around timestep 107, whereas it shifts in lingual direction along the praeparacrista towards the paracone apex on M1. In timestep 30, the buccal flank of the protoconid apex of m1 occludes with the postcingulum of P4, which aids in guiding the lower jaw during further upwards movement, as it restricts the freedom of movement. A second point of occlusion on the distal protoconid flank of m1 occurs with the paracingulum of M1 at timestep 32. With further tooth movement it shifts in cervical direction along the same area of the distal protoconid flank that occludes with the parastyle and paracone. The occlusal contacts between M1 and the distal protoconid flank remain active until the point of centric occlusion. Between timesteps 99 and 125, occlusal contact between the mesial paracone flank along the praeparacrista and the distal hypoconid flank along the posthypocristid occurs. In timestep 82, a first contact occurs between the mesial protocone flank of M1 and the apex of the m1 metaconid. With further tooth movement, this area of contact expands to cover the entire distal metaconid flank and most of the distal protocone flank up to the point of centric occlusion. Initial occlusal contact in the m1 talonid basin occurs in timestep 121 between the entoconid and the distal M1 protocone flank. This area of contact expands to cover the entire entoconid flank with further tooth movement, and a second occlusal contact between the mesial protocone flank and the hypoconulid is initiated in timestep 126. These contacts remain active up until the point of centric occlusion. Additional contacts during centric occlusion are detected at the apex of the M1 protocone, which occludes into the m1 talonid basin, as well as the tip of the m1 hypoconid, which occludes into the M1 talon basin. Also, small contacts are detected between M2 and m2, respectively in the trigonid and trigon basins of the molars. Speothos venaticus (highly carnassialized dentition with trenchant heel) For the OFA analysis of Speothos venaticus , specimen ZFMK MAM 1987 − 0386 was chosen. The power stroke is comprised of 102 timesteps (Fig. 4 b). Initial occlusal contact occurs between the carnassial blades of P4 and m1. It is initially detected between metacone and protoconid and with further upwards movement of the lower jaw a second contact is detected between paracone and metaconid in timestep 6. As the lower molar is moving, these contact areas keep expanding towards the center of the carnassial blades respectively along metacrista and paracristid in direction of the carnassial notches. Around timestep 33, the carnassial notches of P4 and m1 pass each other. Carnassial occlusal contact remains active up until timestep 90. In timestep 13, the first postcarnassial occlusion is detected between the M1 praeparacrista and the distal m1 trigonid flank. With further upwards movement of the lower jaw this contact area shifts in cervical direction along the distal trigonid flank and expands on the mesial paracone flank. Eventually, this contact area shifts into the hypoflexid groove around timestep 86. An additional contact area at the distal trigonid flank is detected at timestep 34 with the M1 paracingulum, which occludes with the apex of the protoconid. This contact area also shifts in cervical direction with further tooth movement along the distal trigonid flank and remains active up until timestep 94. Initial occlusion between the M1 postparacrista and the m1 praehypocristid is detected at timestep 55. This area of contact increases in size with further tooth movement on the mesial hypoconid flank and the distal paracone flank, and eventually shifts into the hypoflexid. Occlusion between hypoflexid and paracone remains active up until the end of the power stroke and is functioning as a guiding contact for the direction of tooth movement. The point of centric occlusion, if it is reached in the dentition of S. speothos , can only be approximated, as there are no post carnassial crushing contacts, which could function as a stopping mechanism. In the OFA analysis, tooth movement was stopped by occlusion of the tip of the m2 main cusp (protoconid) with the distal protocone flank of M1. It is possible that the in vivo power stroke movement is aborted at an earlier point. The extensive wear that was documented in the hypoflexid shows that the occlusion detected in the OFA analysis up until timestep 94 is realistic. OFA analysis of dasyuromorph taxa Dasyurus viverrinus (weakly carnassialized dentition) The teeth of specimen SMF 1480 were chosen for the OFA analysis of Dasyurus viverrinus . Centric occlusion is reached at timestep 162 (Fig. 5 a). Initial contact occurs between the m4 mesial carnassial blade, at the distal-most point of the paracristid below the paraconid, and the M3 distal blade, at the mesial-most point of the metacrista at the metastyle. With the upwards movement of the lower molar, this area of occlusal contact is expanding lingually and thus the active point of cutting is also moving in lingual direction along the paracristid and the metacrista. Initial contact between the paraconid of m4 and the metacone of M3 occurs at timestep 18. This area of occlusal contact is moving in buccal direction with further upwards movement of the lower molar. Starting with timestep 18, there are two points of active cutting between the paracristid and the metacrista, which are both successively expanding their areas towards the center of the two antagonistic cutting blades. At timestep 19, the initial contact between the metacristid of m3, starting at the protoconid, and the praeparacrista of M3, starting at the parastyle, is calculated. With a further upwards movement of the lower molar, cutting beween the metacristid and the praeparacrista eventually includes the whole mesial paracone flank. First occlusal contact between the paracristid of m3 and the metacrista of M2 is calculated at timestep 24, beginning with the lingual point of contact between the paraconid and the metacone. A second part of contact on the buccal side between protoconid and metastyle is calculated at timestep 30. These two contact areas expand with further upwards movement of the lower molar towards the center of the carnassial blade. At timestep 25, initial contact between the metacristid of m4 and the paracrista of M4 is calculated between the apex of the protoconid and the parastyle. This area of occlusal contact successively expands lingually and eventually involves the paracone occluding with the distal carnassial notch. At timestep 96, a second occlusal contact is calculated between the metacristid of m4 and the praeprotocrista of M4, starting with the occlusion of the apices of protocone and metaconid. An additional point of contact between praeprotocrista and metacristid, occurring buccally from the metacristid carnassial notch, is calculated at timestep 109. These two points of cutting between praeprotocrista and metacristid are moving towards the carnassial notch with further upwards movement of the lower molar. The initial occlusal contact between the paracristid of m2, starting at the apex of the protoconid, and the metacrista of M1, starting at the metastyle, is calculated at timestep 73. At timestep 76, a second contact between paracristid and metacrista is calculated, occurring between metacone and paraconid. These two points of occlusal contact are moving towards the center of the carnassial blade with further upwards movement of the lower molar. With this contact, the carnassial blades of m2, m3 and m4 all perform a cutting function while the lower jaw is moving upwards. Initial contact between the metacristid of m2 and the praeparacrista of M2 is calculated at timestep 86. This area of contact expands with further tooth movement towards lingual along the distal paracone flank. A second point of occlusal contact along the metacristid is calculated at timestep 97 and it involves the praeprotocrista. Further upwards movement of the lower jaw results in these two areas of contact moving towards the carnassial notch of the metacristid. The cutting function of m3 metacristid is enhanced by occlusal contact with the praeparacrista of M3 at timestep 102. This area of contact on the lingual part of the metacristid is expanding buccally with further tooth movement, while the occlusal contact with the mesial paracone flank expands lingually onto the mesial protocone flank, with both areas expanding towards the carnassial notch of the lower molar. With this contact, the distal trigonid blades of all lower carnassials perform a cutting function during further tooth movement. In addition to the cutting contacts that are calculated at the mesial and distal trigonid flanks, occlusion also occurs on the talonid. At timestep 91, the first contact between the praemetacrista of M3 and the posthypocristid of m3 occurs. Further upwards movement of m2 results in contact between the praemetacrista of M2 and the posthypocristid of m2 at timestep 100. Initial contact between the postparacrista of M3 and the praehypocristid of m3 occurs at timestep 103. A similar contact at timestep 110 occurs between the postparacrista of M2 and the praehypocristid of m2. With further upwards movement of the lower jaw, the protocones of M2, M3 and M4 move into the talonid basins of the antagonistic lower molars. Occlusal contact in the respective talonid basins successively occurs with the occlusion of the buccal entoconid flank and the postprotocrista. This contact occurs between M3 and m3 in timestep 110, between M2 and m2 in timestep 117 and between M4 and m4 in timestep 131. The calculated contact area shifts into the talonid basins of all lower molars and onto the buccal protocone flank of the upper molars with further upwards movement of the lower jaw. This upwards movement is stopped at timestep 162, when the point of centric occlusion is reached. Thylacinus cynocephalus (highly carnassialized dentition with trenchant heel) For the OFA analysis of Thylacinus cynocephalus , specimen ZMB_Mam_036877 was chosen. The complete chewing path is comprised of 168 steps and consists of one single phase until the point of centric occlusion is reached (Fig. 5 b). Initial occlusal contact occurs between the metacrista of M3, starting on the buccal side in proximity to the metastyle, and the distalmost point of the m4 paracristid, in proximity to the apex of the paraconid. With further upwards movement of the lower molars, this contact area expands in mesial direction towards the carnassial notch of m4 and in direction of the metacone of M3. In timestep 18 the first contact between the M3 metacone and the m4 protoconid occurs, marking a second point of occlusion between the M3 and m4 carnassial blades. Both contact areas keep expanding on the occluding flanks and approach each other with further tooth movement, eventually wrapping around the carnassial notch of the lower molar and fusing in timestep 58. In timestep 31, occlusal contact occurs between the mesial paracone flank of M3 and the distal trigonid flank of m3. With further tooth movement, this contact area expands along the praeparacrista and postparacrista of M3 and along the distal trigonid flank of m3 in cervical direction. This occlusal contact remains up until timestep 120. In timestep 61, two points of contact between the carnassial blades of M2 and m3 are detected. The first occurs on the buccal side, in proximity to the metastyle and the protoconid. The second contact occurs on the lingual side, in proximity to the metacone and the paraconid. Both contacts expand with further tooth movement, approximating each other along the metacrista and the paracristid. Eventually, they wrap around the carnassial notch of m3 and fuse in timestep 99. First contact between the mesial paracone flank of M2 and the distal trigonid blade of m2 occurs in timestep 62. With further tooth movement, the area of occlusal contact expands along the postparacrista and the praepacacrista of M2 and expands in cervical direction of both antagonistic flanks and remains up until timestep 127. In timestep 86, the first occlusal contact between the carnassial blades of M1 and m2 is detected. It occurs on the buccal side of the blades between the metastyle of M1 and the protoconid of m2. With further upwards movement of the lower molars, this contact area expands in lingual direction along the metacrista and the paracristid. A second point of contact on the lingual side is detected in timestep 97. It occurs between the metacone of M1 and the paraconid of m2. With further tooth movement, this contact expands in lingual direction. Both areas of contact approximate each other in the following timesteps and merge in timestep 118, wrapping around the carnassial notch of the lower molar. The first contact between the mesial paracone flank of M4 and the distal trigonid flank of m4 occurs in timestep 53. This contact remains during most of the rest of the chewing path, with the distal trigonid flank of m4 occluding along the paracone of M4 up until 15 timesteps before centric occlusion. Eventually, the contact wraps around the paracone and covers the hypoflexid. In addition to the trigonids occluding with the paracones and metacones, there are occlusal contacts between the talonids and the paracones and metacones. The first contact occurs in timestep 63 between the distal talonid flank of m3 and the mesial metacone flank of M3. It starts on the lingual side, along the praemetacrista in proximity to me metacone and along the posthypocristid in proximity to the hypoconulid. With further tooth movement, this occlusal contact expands in buccal direction along the praemetacrista and along the posthypocristid towards the hypocone. This occlusion remains until timestep 112. In timestep 100, the first occlusal contact between the distal paracone flank of M3 and the mesial talonid flank of m3 is detected. This contact area remains small and is only active for a shorter duration, up until timestep 136. The first occlusal contact between the distal talonid flank of m2 and the mesial metacone flank of M2 occurs in timestep 107 on the lingual side. The area of contact expands with further tooth movement along the praemetacrista in lingual direction from the metacone and from the hypoconulid towards the hypoconid. It remains active until timestep 131.The mesial talonid flank of m2 occludes with the distal paracone flank of M2 first in timestep 133. The area of contact remains small and is active until timestep 155. Discussion The documented tooth wear as well as the OFA analysis both point to an emphasized shearing function of the unicuspid talonid in carnivoran and dasyuromorph carnassials, with a subordinate guiding component. The lingual cusps of the upper carnassials (paracone + metacone or metastyle) and the connecting crests are aligned longitudinally from mesial to distal, to increase the shearing function. Occlusion occurs between the carnassial blades and between the distal paracone and mesial talonid flank. The crown structure of the lower carnassials remains more conservative in carnivorans and dasyuromorphs, while more apomorphic adaptations are present in the upper dentition. Differences in the crown morphology of the upper teeth in return result in some occlusal differences between carnivorans and dasyuromorphs. In marsupials, which have multiple carnassial teeth, additional occlusion occurs between the mesial metacone flank and the distal talonid flank (except for the last lower carnassial, which lacks a distal upper antagonist). Occlusal contact between the buccal protocone flank and the lingual hypoconid flank is generally reduced in carnassials with unicuspid talonids, indicating loss of the crushing function. For Thylacinus cynocephalus a short period of occlusion between protocone and hypoconid was calculated at the end of the power stroke in the OFA reconstruction, which then acts as a terminal “stopping” point for the tooth movement. The reduction of two talonid cusps (entoconid and hypoconulid) and loss of the basined talonid in carnassials allows an enlargement of the mesial talonid (hypoconid) flank and thus the opening of the hypoflexid groove, which connects to the distal trigonid flank. As a result, the shearing function of the trenchant talonid is enhanced. In carnassial teeth with tricuspid talonids, as in Dasyurus viverrinus , Ichneumia albicauda , Viverra tangalunga and Viverra zibetha , and the presence of multiple facets within the talonid basin points to a stronger emphasis on a crushing function, while the paracone/hypoflexid function is only weakly pronounced. The OFA reconstructions also revealed a functional difference, with a shorter paracone/hypoflexid occlusal contact before centric occlusion in Dasyurus viverrinus (27% of timesteps) and Viverra tangalunga (12%) than in Speothos venaticus (46%) and Thylacinus cynocephalus (35%). In all taxa, steeply lingually inclined striations on the facets indicate a mostly orthal tooth movement during the power stroke, to which the paracone/hypoflexid occlusion contributes in the strongly carnassialized condition with a trenchant heel. Solé & Ladevèze ( 2017 ) postulated a cusp reduction in carnassials in reverse sequence of the patterning cascade mode of cusp development as formulated by Jernvall ( 1995 , 2000 ) and Jernvall and Jung ( 2000 ), although a decoupling of metaconid and talonid development in carnassials is noted. Further, the resemblance of carnassials to the molariforms of mammaliaforms and early mammals, especially the morganucodontans and eutriconodontans, due to the linear alignment of cusps and absence of a triangular tooth crown, is noted (Solé & Ladevèze 2017 ). The reuse of the hypoflexid groove for shear-cutting in carnassials apparently is linked to the sequential reduction of cusps (with the hypoconid being the last cusp to get reduced). Cusp d of the triconodont teeth of morganucodontans, generally regarded as a the initial talonid cusp, did not perform a major cutting function. Jäger et al. ( 2019 ) showed occlusal relationships in triconodont teeth of Morganucodon and Megazostrodon which differ from those seen in carnassials, with the mesial flank of cusp C (metacone) occluding with cusp d (hypoconid). The main piercing and cutting function are performed by cusp A (paracone), as it is the main cusp of the upper molar. Cusp A occludes with the mesial flank of cusp c (metaconid), and not with cusp d (Jäger et al. 2019 ). Occlusion of cusp A and cusp d is established later in mammalian evolution, after triangulation of the trigon and trigonid cusps. At this point the occlusal relationships become comparable to those of carnassial teeth with a unicuspid talonid, where cusp A (paracone) is occluding between the unicuspid talonid cusp and cusp a (protoconid). Thus, a groove exhibiting functional resemblance to the hypoflexid of the tribosphenic molar (and its derivatives) is present in morganucodontan teeth. Whether the presence of the hypoflexid groove in carnassials is a result of the reduction of cusps based on the patterning cascade mode, suggesting structural homology, remains ambiguous, as the identity of the first talonid cusp to evolve (hypoconid or hypoconulid) is debated (Davis 2011 ). Eutriconodontan molars are another good functional equivalent to carnassials, as they also emphasize the cutting function, with cusp d increasing in size and being integrated in the cutting function (Jäger et al. 2020 ). In some late surviving morganucodontans from the Upper Jurassic, cusp c is enlarged, as seen in Storchodon cingulatus (Martin et al. 2024 ). This results in a lower molar morphology that is strikingly similar to lower carnassials with a unicuspid talonid. In these teeth, a groove forms between cusps a and c, which structurally resembles the hypoflexid groove of carnassials with unicuspid talonid. The structural resemblance between carnassial teeth and triconodont teeth, where the cusps are aligned along the longitudinal axis, is the result of the functional requirements of a meat-cutting dentition, which favors longitudinally aligned cutting blades. The pronounced hypoflexid groove in carnassial teeth provides an additional shearing locus between the paracone and the unicuspid talonid, which is further enhanced by the more simplified talonid morphology of highly carnassialized teeth (Fig. 6 ). It is interesting to note that in all investigated taxa which exhibit a carnassial with unicuspid talonid, a small notch is present between the hypoconid and the distal trigonid flank. This notch increases the cutting efficiency, as it duplicates the function of the main carnassial notch at a smaller scale. The striations on the facets associated with the paracone/hypoflexid occlusion of the carnassials show a uniform orientation. They indicate that the slightly obliquely inclined tooth movement, as initiated with carnassial blade occlusion, is maintained during the power stroke. This function is comparable to some extent to the hypoflexid function in cladotherian dryolestidans, although the guiding component is more pronounced in these pretribosphenic teeth than in the carnassials (Schultz & Martin 2011 ; 2014 ). A change of the inclination of the striations on the distal trigonid flank near the hypoflexid, as observed in dryolestidan molars (Schultz & Martin 2011 ), was not observed in the hypoflexids of carnassial teeth. Thus, a crushing component, which would result in a change of striation inclination, cannot be inferred for the carnassial trenchant heel. The guiding function of paracone/hypoflexid occlusion in carnassials can be attributed to the effect of “autocclusion”, a term that has been coined to refer to the occlusal alignment of cusps during tooth movement being controlled by the morphology of the teeth (Mellett, 1985 ). Autocclusion limits the neurological requirements for tooth alignment to the initial occlusal contact of the power stroke (Evans & Sanson, 2006 ). The development of a trenchant unicuspid talonid with a shearing hypoflexid evolved multiple times from the tribosphenic pattern in therians with carnassial adaptations, resulting in similar occlusal patterns, indicating an increase in faunivory. The therian carnassials with pronounced hypoflexid exhibit a remarkable structural resemblance to molariforms of non-tribosphenic mammaliaforms and mammals, such as morganucodontans and eutriconodontans, as well as pretribosphenic dryolestidans. Due to their small body size, morganucodontans and dryolestidans relied on an insectivorous and invertebrate diet (Gill et al. 2014 ; Schultz & Martin, 2014 ). Some eutriconodontans, however, reached larger body sizes, such as Repenomamus giganticus with an estimated body mass of 12–14 kg (Hu et al. 2005 ), representing the largest known Mesozoic mammal. Repenomamus and other large-bodied eutriconodontans such as Gobiconodon were predators and/or scavengers, antedating the therian carnivorous adaptation at the non-tribosphenic level. In therians, the carnassialization of the molars was acquired by a reduction of the tribosphenic pattern, functionally getting back to the pretribosphenic condition. Declarations Acknowledgements We thank Julia Schultz (Bonn) for the provision of scan data of D. leiriensis . For the loaning of specimens, we thank Loïc Costeur (NMB), Jan Decher (ZFMK), Eberhard (Dino) Frey (formerly SMNK), Christiane Funk (ZMB), Jörn Köhler (HLMD), Katrin Krohmann (SMF), Frieder Mayer (ZMB) and Irina Ruf (SMF, Senckenberg Gesellschaft für Naturforschung). This research was funded by a doctoral grant to A. J. Lang by the Studienstiftung des deutschen Volkes. Open access funding enabled and organized by project DEAL. Author contributions Both authors contributed to the study conception and design. Casting, tooth wear documentation, scanning and OFA analyses were performed by AJL. The first draft of the manuscript was written by AJL. AJL and TM contributed critically to previous versions of the manuscript. Funding This study was funded by a doctoral grant to A. J. Lang by the Studienstiftung des deutschen Volkes. Competing Interests The authors declare no conflict of interest. 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Naturwissenschaften 101:771–781. https://doi.org/10.1007/s00114-014-1214-y Schultz JA, Menz U, Winkler DE, Schulz-Kornas E, Engels S, Kalthoff DC, von Koenigswald W, Ruf I, Kaiser TM, Kullmer O, Südekum KH, Martin T (2017) Modular Wear Facet Nomenclature for mammalian post-canine dentitions. Historical Biology 30(1–2):30–41. https://doi.org/10.1080/08912963.2017.1302442 Solé, F, Ladevèze S (2017) Evolution of the hypercarnivorous dentition in mammals (Metatheria, Eutheria) and its bearing on the development of tribosphenic molars. Evolution & Development 19:56–68. https://doi.org/10.1111/ede.12219 Tarquini SD, Chemisquy MA, Prevosti FJ (2020) Evolution of the carnassial in living mammalian carnivores (Carnivora, Didelphimorphia, Dasyuromorphia): Diet, phylogeny, and allometry. Journal of Mammalian Evolution 27:95–109. https://doi.org/10.1007/s10914-018-9448-7 Thenius E (1989) Tlbd/Part 56 Zähne und Gebiß der Säugetiere. De Gruyter, Berlin, Boston. https://doi.org/10.1515/9783110856927 Van Valkenburgh B (1991) Iterative Evolution of Hypercarnivory in Canids (Mammalia: Carnivora): Evolutionary Interactions Among Sympatric Predators. Paleobiology 17(4):340–362. https://doi.org/10.1017/S0094837300010691 Van Valkenburgh B (2007) Déjà vu: the evolution of feeding morphologies in the Carnivora. Integrative and Comparative Biology 47:147–163. https://doi.org/10.1093/icb/icm016 Van Valkenburgh B, Wayne RK (2010) Carnivores. Curr Biol 20(21):R915–919. https://doi.org/10.1016/j.cub.2010.09.013 Wortman JL, Matthew WD (1899). The ancestry of certain members of the Canidae, the Viverridae, and Procyonidae. Bulletin of the American Museum of Natural History 12:109–38. http://hdl.handle.net/2246/1535 Cite Share Download PDF Status: Published Journal Publication published 09 Sep, 2024 Read the published version in Mammal Research → Version 1 posted Reviewers agreed at journal 28 Jun, 2024 Reviewers invited by journal 24 Jun, 2024 Editor assigned by journal 21 Jun, 2024 First submitted to journal 21 Jun, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4610245","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":318283555,"identity":"509f3d6e-14a2-4855-aaf9-f959827e57f1","order_by":0,"name":"Andreas Lang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAvElEQVRIiWNgGAWjYFCCww1AwgbMlCBSy0GQljSStDCCtBwmQQt/48HGzwW/ztutnZHAeOMDMVokDhxslp7Zdzt525kDzJYziLLmwMEGad6e28lmxxvYpHmI0SEPtOU3b8+5ZLPDDGzSf4jRYnDgYJs0z48DdmBbiHKXIVCLNW9DcoLZmYPNlj3EaJG7cfjwbZ4/dvZmN5IP3vhBlDUSB4BR08aQ2ACJIGIAP0jhHwZ7IpWPglEwCkbBSAQAeIM7007bYjQAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0003-3467-1972","institution":"Rheinische Friedrich-Wilhelms-Universitat Bonn","correspondingAuthor":true,"prefix":"","firstName":"Andreas","middleName":"","lastName":"Lang","suffix":""},{"id":318283556,"identity":"d1dae656-0280-4b31-a4f3-369737265cdd","order_by":1,"name":"Thomas Martin","email":"","orcid":"","institution":"Rheinische Friedrich-Wilhelms-Universitat Bonn","correspondingAuthor":false,"prefix":"","firstName":"Thomas","middleName":"","lastName":"Martin","suffix":""}],"badges":[],"createdAt":"2024-06-20 08:17:35","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4610245/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4610245/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s13364-024-00762-1","type":"published","date":"2024-09-09T15:57:44+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":60625664,"identity":"9165f569-c3fc-4612-b80c-ebb877ecf24c","added_by":"auto","created_at":"2024-07-18 22:26:21","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":70160,"visible":true,"origin":"","legend":"\u003cp\u003eThe carnassialized and postcarnassial teeth of \u003cem\u003eSpeothos venaticus\u003c/em\u003e (P4, M1, m1) and \u003cem\u003eThylacinus cynocephalus\u003c/em\u003e (M3, M4, m4) in comparison to upper and lower molars of the non-tribosphenic morganucodontid \u003cem\u003eStorchodon cingulatus\u003c/em\u003e and of the pre-tribosphenic cladotherian \u003cem\u003eDryolestes leiriensis\u003c/em\u003e (both molars mirrored). Blue arrows indicate the presence of a hypoflexid or hypoflexid-like groove on the lower molars.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4610245/v1/0f9a48774f8370941fcb8e3f.jpg"},{"id":60625666,"identity":"a5cd4a47-ef91-4d1e-a3c8-174b904f325c","added_by":"auto","created_at":"2024-07-18 22:26:21","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":123537,"visible":true,"origin":"","legend":"\u003cp\u003eTooth wear on the m1 (a) and M1 (b) of \u003cem\u003eDinictis\u003c/em\u003esp. (SMNK-PAL 9090) and on the m1 (c) and M1 (d) of \u003cem\u003eSpeothos venaticus\u003c/em\u003e (ZFMK MAM 1992.0565). Dashed lines mark the visible edges of facets. Solid lines indicate the inclination of striations. Photographs of epoxy casts.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4610245/v1/496841079329ba5058bc63cd.jpg"},{"id":60626152,"identity":"ad369782-1298-4c61-8b6d-b9aab875c8b2","added_by":"auto","created_at":"2024-07-18 22:34:21","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":107332,"visible":true,"origin":"","legend":"\u003cp\u003eTooth wear on m4 (a) and M4 (b) of \u003cem\u003eSarcophilus harrisii\u003c/em\u003e (NMB 10548) and on m4 (c) and M4 (d) of \u003cem\u003eThylacinus cynocephalus\u003c/em\u003e (NMB 2526). Dashed lines mark the visible edges of facets. Solid lines indicate the inclination of striations. Photographs of epoxy casts.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4610245/v1/9a32fe6f27472d1e5ee0b427.jpg"},{"id":60626153,"identity":"6f03465b-1d0c-4827-928c-fe84f1158510","added_by":"auto","created_at":"2024-07-18 22:34:21","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":78406,"visible":true,"origin":"","legend":"\u003cp\u003eResults of the OFA-analysis of the power strokes of \u003cem\u003eViverra tangalunga\u003c/em\u003e and \u003cem\u003eSpeothos venaticus\u003c/em\u003e, showing the total occlusal area from the initial occlusal contact up to the point of centric occlusion. Duration of the carnassial blade occlusion (cbo) and hypoflexid occlusion (hyo) are indicated. Occlusal contact (red markings) in selected timesteps is indicated on the lower m1 and m2 in occlusal view (lingual is up and mesial is to the right). Tooth models 3D renderings from µCT data.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4610245/v1/c6e9c4cf718ef781bc4ae828.jpg"},{"id":60625667,"identity":"3c02e222-cf8b-44e4-badc-7528a4b7b727","added_by":"auto","created_at":"2024-07-18 22:26:21","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":84317,"visible":true,"origin":"","legend":"\u003cp\u003eResults of the OFA-analysis of the power strokes of \u003cem\u003eDasyurus viverrinus\u003c/em\u003e and \u003cem\u003eThylacinus cynocephalus\u003c/em\u003e, showing the total occlusal area from the initial occlusal contact up to the point of centric occlusion. Duration of the carnassial blade occlusion (cbo) and hypoflexid occlusion (hyo) is indicated respectively. Occlusal contact (red markings) in selected timesteps is indicated on the lower m2 to m4 in occlusal view (lingual is up and mesial is to the right). Tooth models 3D renderings from µCT data.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4610245/v1/ddc269b6cb0a227a00a440f1.jpg"},{"id":60625668,"identity":"c51f5be8-6b28-41dd-8686-8effca489c81","added_by":"auto","created_at":"2024-07-18 22:26:21","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":88636,"visible":true,"origin":"","legend":"\u003cp\u003eEvolutive connection of carnassialization and the “trenchant” talonid heel as exemplified in carnivoran and dasyuromorph taxa. Carnassial occlusal contact (red) and paracone/hypoflexid occlusal contact (blue) both increase up to the point where the talonid is completely reduced (as in \u003cem\u003eFelis silvestris\u003c/em\u003e). Upper molars in occlusal view, lower molars in buccal view. Mesial is to the right.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4610245/v1/ebf92473cd3af95655fb5859.jpg"},{"id":64619512,"identity":"e5c77157-da19-44e0-9417-5078d561f088","added_by":"auto","created_at":"2024-09-16 16:15:29","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1226241,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4610245/v1/bc4a7a3b-102f-44fc-b61c-005e5f54b91b.pdf"}],"financialInterests":"","formattedTitle":"Hypoflexid function in the “trenchant heel” of carnassial teeth, with comments on talonid evolution","fulltext":[{"header":"Introduction","content":"\u003cp\u003eCarnassial teeth, specialized for the slicing of meat, evolved convergently among carnivorous mammals, i. e. the Carnivora, Hyaenodonta, Oxyaenodonta and Dasyuromorphia (De Muizon \u0026amp; Lange-Badr\u0026eacute; \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Van Valkenburgh \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2007\u003c/span\u003e, Tarquini et al., 2018). Generally, carnassials are characterized by a secondary reduction of features seen in tribosphenic teeth. Tribosphenic teeth combine the slicing function of the trigonid with the crushing function of the upper molar protocone and the lower molar talonid basin (Crompton \u0026amp; Hiimae 1969; Crompton \u0026amp; Hiimae 1970; Luo et al. 2003). With increasing carnassialization, the protocone of the upper carnassial and the metaconid and talonid cusps (entoconid, hypoconid and hypoconulid) of the lower carnassial are reduced (Lang et al. 2021). This results in a morphology which emphasizes the postvallum/prevallid slicing function and reduces the protocone/talonid crushing function (De Muizon \u0026amp; Lange-Badr\u0026eacute; \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1997\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe Carnivora are the most diverse extant clade of carnivorous mammals in terms of species and ecomorphology, with the upper P4 and the lower m1 forming the carnassial teeth, while the more distal molars represent the post-carnassial crushing part of the dentition (Van Valkenburgh \u0026amp; Wayne \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Some extant species of the marsupial Didelphimorphia and Dasyuromorphia also evolved carnassial teeth, with the upper M1-M3 and the lower m2-m4 forming three pairs of carnassials (Tarquini et al. 2018). The distalmost carnassials in marsupials (M3/m4) are the \u0026ldquo;principal carnassials\u0026rdquo;, exhibiting the most carnassialized condition of the tooth row (Butler \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1946\u003c/span\u003e; Tarquini et al. 2018; Lang et al. 2021). Generally, the carnassials of carnivorans and marsupials exhibit similar structural modifications, although the upper carnassial blade of carnivorans is between the paracone and the distally displaced metacone, whereas it is between the metacone and the distally displaced metastyle in marsupials (Sol\u0026eacute; \u0026amp; Ladev\u0026egrave;ze, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe grade of talonid reduction in carnassialized teeth varies between taxa. The carnassials of canids retain a basined talonid which performs a crushing function, although the hypoconulid is reduced in some species such as \u003cem\u003eCanis lupus\u003c/em\u003e (Berkovitz \u0026amp; Shellis \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). In the most extreme carnassialized teeth as seen in felids, the talonid is completely absent (Thenius \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e1989\u003c/span\u003e). In some species, carnassialization results in a unicuspid talonid which has been termed \u0026ldquo;trenchant heel\u0026rdquo; (Wortman \u0026amp; Matthew \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e1899\u003c/span\u003e). The trenchant heel is usually interpreted to serve as a secondary cutting feature, with the enlarged single talonid cusp (hypoconid) functioning as an additional cutting blade (Van Valkenburgh \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e1991\u003c/span\u003e). Carnassials with a unicuspid trenchant talonid evolved multiple times within the Carnivora. Among extant Caniformia, it is present in \u003cem\u003eCuon alpinus\u003c/em\u003e, \u003cem\u003eLycaon pictus\u003c/em\u003e, and \u003cem\u003eSpeothos venaticus\u003c/em\u003e (Berkovitz \u0026amp; Shellis \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Within the Feliformia, it evolved in the extinct Nimravidae (e. g. \u003cem\u003eNimravus\u003c/em\u003e) (Peign\u0026eacute; et al. 2000). In the carnassials of the marsupial Dasyuromorphia, a reduced unicuspid talonid evolved in \u003cem\u003eSarcophilus harrisii\u003c/em\u003e and \u003cem\u003eThylacinus cynocephalus\u003c/em\u003e (Thenius \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e1989\u003c/span\u003e). A possible inhibition of the development of certain crown features has been linked to a \u0026ldquo;structural reversal\u0026rdquo; of the carnassial crown structure towards the pretribosphenic condition. These structural changes include cusp reduction and a change of the crown topology to a mesio-distal alignment of the remaining cusps, resembling the molariform teeth of the Mesozoic Morganucodonta and Eutriconodonta (Sol\u0026eacute; \u0026amp; Ladev\u0026egrave;ze, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). This inferred resemblance is purely based on morphological similarities, while a functional comparison with carnassial teeth has not been carried out so far. In pretribosphenic molars as seen in dryolestidans, the single talonid cusp and the distal trigonid flank are separated by a deep hypoflexid groove. The groove served as a guiding structure for the upper molar paracone during the power stroke and performed a shearing function with crushing component (Schultz \u0026amp; Martin, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). In more derived tribosphenic molars, the hypoflexid is reduced and has lost the guiding function. Crushing is instead performed by occlusion of the upper molar protocone into the talonid basin (Schultz \u0026amp; Martin, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The observed structural similarities between the unicuspid talonids of carnassial and pretribosphenic teeth (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) suggest an analogous function.\u003c/p\u003e \u003cp\u003eWhile tooth function of the mammaliaform Morganucodonta relied mostly on puncturing and shearing and less so on precise cutting, eutriconodontans involved all serially arranged cusps into the cutting function, including the distal-most cusp d of the lower molariform (J\u0026auml;ger et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Cusp d is hypothesized to be the initial talonid cusp, although the homology of the talonid cusps of the tribosphenic molar is debated (Davis \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThere is a structural resemblance between pretribosphenic molars and carnassial teeth with a trenchant heel, both exhibiting a reduced morphology of the tribosphenic condition with multicuspid talonid. This raises the question, if there occurred a functional shift in carnassials with trenchant heel, with a replacement of the protocone/talonid occlusion by a paracone/hypoflexid occlusion, similar to the situation in pretribosphenic molars.\u003c/p\u003e \u003cp\u003eThe objective of this study is to elucidate the functional role of the hypoflexid groove in carnassial teeth with trenchant heel and in which aspects the trenchant heel is functionally comparable to the distal portion of non-tribosphenic (cusp c\u0026thinsp;+\u0026thinsp;d) and pretribosphenic (cusp d [hypoconulid]) teeth.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eNine species with different degrees of carnassialization were studied (list of specimens in Online Resource 1). These include six carnivoran species, with \u003cem\u003eIchneumia albicauda\u003c/em\u003e, \u003cem\u003eViverra tangalunga\u003c/em\u003e and \u003cem\u003eViverra zibetha\u003c/em\u003e representing a weakly carnassialized condition with a tricuspid talonid, \u003cem\u003eSpeothos venaticus\u003c/em\u003e and \u003cem\u003eDinictis\u003c/em\u003e sp. representing the carnassial condition with a unicuspid trenchant heel and \u003cem\u003eFelis silvestris\u003c/em\u003e representing the highly carnassialized condition with a completely reduced talonid. For the marsupials, the dasyuromorph \u003cem\u003eDasyurus viverrinus\u003c/em\u003e represents the weakly carnassialized condition with a tricuspid talonid and \u003cem\u003eSarcophilus harrisii\u003c/em\u003e and \u003cem\u003eThylacinus cynocephalus\u003c/em\u003e represent the condition with a unicuspid trenchant heel, which is the most carnassialized condition among dasyuromorphs.\u003c/p\u003e \u003cp\u003eTooth wear was documented using the digital microscope AXIO Zoom V16 (Zeiss, Oberkochen, Germany). Pictures were generated from image stacks of 20 to 30 focal planes, using the augmented focus depth function of the ZEN pro software (Zeiss). The wear was documented with epoxy resin casts. The Provil \u0026reg; novo Light regular set (Heraeus Kulzer, Hanau, Germany) was used to create molds of the teeth. It has a high casting accuracy of \u0026lt;\u0026thinsp;0.1 mm and thus can be used to document microwear on the tooth surface. Casts were made using the RenLam \u0026reg; M-1 (Huntsman Advanced Materials, Bergkamen, Germany) epoxy resin and the Ren \u0026reg; HY 956 (Huntsman Advanced Materials) hardener. For coloration of the casts, the Araldite \u0026reg; DW 0137 Colouring Paste (Huntsman Advanced Materials) was used.\u003c/p\u003e \u003cp\u003eDocumentation of tooth wear was used to characterize the function of the examined teeth. Occlusal contact between antagonistic teeth results in attrition, which produces polished wear facets on the enamel surface that indicate which crown structures are involved in the occlusal interaction (Butler, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1952\u003c/span\u003e). Parallel striations on these attritional facets indicate the relative tooth movement (Butler, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1972\u003c/span\u003e). Mapping of the facets can be used to determine complementary occlusal crown structures and compare the function of different teeth during the power stroke, which is the section of the chewing movement during which occlusal contact occurs (Crompton 1972, Schultz et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). For facets, we use the modular nomenclature of Schultz et al. (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), which is based on the topographic position of facets (list of abbreviations in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe teeth were scanned with the v|tome|x s \u0026micro;CT (GE Sensing \u0026amp; Inspection Technologies GmbH phoenix|X-ray, Wunstorf, Germany) of the Bonn Institute of Organismic Biology, Section Paleontology, University of Bonn, Germany. Isotropic scanning resolution varied between 40.9969 \u0026micro;m and 64.017 \u0026micro;m (scanning resolutions are listed in Online Resource 1). The scans of specimens MG Gui Mam 1150 and MG Gui Mam 1155 (\u003cem\u003eDryolestes leiriensis\u003c/em\u003e) were provided by Julia Schultz. For comparison to the teeth of \u003cem\u003eStorchodon cingulatus\u003c/em\u003e, scans of the specimens NLMH 100023 and NLMH 105654, described in Martin et al. (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2019\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), were used. For segmentation, the software Avizo 8 (Thermo Fisher Scientific, Waltham, MA, USA) was used. For further mesh editing and orientation, the software PolyWorks 2015 IR 13 (InnovMetric Software Inc., Montreal, Quebec, Canada) was used.\u003c/p\u003e \u003cp\u003eThe Occlusal Fingerprint Analyser (OFA), developed within the DFG Research Unit 771, enables a virtual reconstruction of the power stroke. For the reconstruction, 3D-surface models of antagonistic molars are imported into the software, and are subsequently brought into occlusion via movement in virtual space (Benazzi et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Kullmer et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2009\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe power strokes of two carnivorans (\u003cem\u003eViverra tangalunga\u003c/em\u003e [Online Resource 2] and \u003cem\u003eSpeothos venaticus\u003c/em\u003e [Online Resource 3]) and two dasyuromorphs (\u003cem\u003eDasyurus viverrinus\u003c/em\u003e [Online Resource 4] and \u003cem\u003eThylacinus cynocephalus\u003c/em\u003e [Online Resource 5]) were reconstructed using the OFA software. For the OFA analysis, the carnassials (P4 and m1 of Carnivora, M1-M3 and m2-m4 of Dasyuromorphia) and non-carnassialized posterior teeth (M1 and m2 of Carnivora, M4 of Dasyuromorphia) were used. The 3D model for each single tooth was reduced to a maximum of 50,000 triangles before the analysis using the mesh optimization tool of PolyWorks. Antagonistic tooth rows were positioned in centric occlusion, which is the point of maximum intercuspation sensu Crompton \u0026amp; Hiiemae (1970), using the manual alignment tools of PolyWorks. In tribosphenic teeth, the power stroke is divided into two phases, during the closing and the opening movement of the lower jaw, respectively (Crompton \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1971\u003c/span\u003e). Only the power stroke, when occlusal contacts occur, can reliably be reconstructed with the OFA. The occlusal contacts produce wear facets that can be quantified and that indicate the chewing movements. The directions of the preliminary stroke and the recovery stroke sensu Crompton and Hiiemae (1969) were extrapolated from the movements of the teeth in phase I and phase II (if present). If no phase II is present, a simple orthal jaw opening movement was assumed.\u003c/p\u003e \u003cp\u003eThe simulation of the chewing stroke with detection of occlusal contacts, direction of movement and inclination of wear facets via OFA analysis was used to analyze the mode of hypoflexid occlusion. The size of the area of occlusal contact per timestep was visualized by contact diagrams.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eList of abbreviations for crown structures, positions of facets and institutions.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eAbbreviations for crown structures of mammalian molars\u003c/p\u003e \u003cp\u003e(modified after Schultz et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2017\u003c/span\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eed\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEntoconid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ehd\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHypoconid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ehld\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHypoconulid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMEC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMetacrista\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eME\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMetacone\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003emd\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMetaconid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMTS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMetastyle\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePACL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eParacingulum\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eParacone\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003epa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eParaconid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePAS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eParastyle\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eProtocone\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003epr\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eProtoconid\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePositions of facets\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ebuccal\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ed\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003edistal\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003el\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003elingual\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003em\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003emesial\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eInstitutional abbreviations\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHLMD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHessisches Landesmuseum Darmstadt, Germany\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMG\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMuseu Geol\u0026oacute;gico (Lisbon) of National Laboratory of Energy and Geology of Portugal\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNLMH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNieders\u0026auml;chsisches Landesmuseum Hannover, Germany\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNMB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNaturhistorisches Museum Basel, Switzerland\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSMF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSenckenberg Naturmuseum Frankfurt, Germany\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSMNK\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStaatliches Museum f\u0026uuml;r Naturkunde Karlsruhe, Germany\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZFMK\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eZoologisches Forschungsmuseum Alexander Koenig, Bonn, Germany\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZMB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMuseum f\u0026uuml;r Naturkunde, Humboldt-Universit\u0026auml;t zu Berlin, Germany\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":"Results","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eCrown structure of carnivoran and dasyuromorph carnassial teeth\u003c/h2\u003e \u003cp\u003eThe carnassialized teeth of carnivorans and dasyuromorphs are structurally more similar in the lower jaw than in the upper jaw. The lower carnassial teeth are characterized by an enlargement of the paracristid, which forms the V-shaped carnassial blade between the paraconid and the protoconid. On the weakly carnassialized teeth of \u003cem\u003eIchneumia albicauda\u003c/em\u003e, \u003cem\u003eViverra tangalunga\u003c/em\u003e, \u003cem\u003eViverra zibetha\u003c/em\u003e and \u003cem\u003eDasyurus viverrinus\u003c/em\u003e, the hypoconid is the most prominent cusp of the talonid, with the hypoconulid and the entoconid being smaller.\u003c/p\u003e \u003cp\u003eIn more strongly carnassialized teeth, the metaconid is reduced (as in \u003cem\u003eS. venaticus\u003c/em\u003e and \u003cem\u003eSpeothos harrisii\u003c/em\u003e) or completely absent (as in \u003cem\u003eDinictis\u003c/em\u003e sp. and \u003cem\u003eThylacynus cynocephalus\u003c/em\u003e). The only prominent cusp of the talonid is the hypoconid.\u003c/p\u003e \u003cp\u003eThe upper carnassialized teeth of carnivorans and dasyuromorphs differ in the construction of the carnassial blade. As the blade extends between the metacone and the paracone in carnivorans, the paracone is the only lingual cusp besides the small protocone, which gets reduced in more strongly carnassialized teeth (e.g. \u003cem\u003eF. silvestris\u003c/em\u003e). In contrast to carnivorans, the carnassial blade of dasyuromorphs extends between the metastyle and the metacone, thus the metacone and the paracone are both present as lingual cusps besides the protocone. As in carnivorans, the protocone is reduced in more strongly carnassialized dasyuromorph teeth (as in \u003cem\u003eS. harrisii\u003c/em\u003e and \u003cem\u003eT. cynocephalus\u003c/em\u003e). Overall, the metacone is larger than the paracone in dasyuromorph carnassials. On the M4, however, which is the only upper molar lacking a carnassial adaptation, the paracone is larger than the metacone in all studied taxa, as the entire distal portion of the tooth is reduced.\u003c/p\u003e \u003cp\u003eWhile the metacone is part of the carnassial blade on the carnivoran P4, it is smaller than the paracone on the post-carnassial M1, which is lacking a carnassial blade. This pattern is seen in the weakly carnassialized teeth of \u003cem\u003eIchneumia albicauda\u003c/em\u003e, \u003cem\u003eViverra tangalunga\u003c/em\u003e and \u003cem\u003eViverra zibetha\u003c/em\u003e as well as the higher carnassialized teeth of \u003cem\u003eDinictis\u003c/em\u003e sp. and \u003cem\u003eSpeothos venaticus\u003c/em\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eTooth wear in carnivoran taxa\u003c/h2\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003eProtocone-talonid-occlusion\u003c/h2\u003e \u003cp\u003eIn the weakly carnassialized teeth of \u003cem\u003eI. albicauda\u003c/em\u003e, \u003cem\u003eV. tangalunga\u003c/em\u003e and \u003cem\u003eV. zibetha\u003c/em\u003e, there are facets on the outer buccal margin of the talonid as well as within the talonid basin. Occlusion of the distal protocone flank of the M1 with the mesial flanks of entoconid and hypoconulid of the m1 is indicated by the presence of facets ed-mb, hld-mb and PR-dl. The mesial flanks of the entoconid and the hypoconulid appear polished in \u003cem\u003eI. albicauda\u003c/em\u003e and \u003cem\u003eViverra\u003c/em\u003e spp., indicating attritive wear. Striations running from the apices in cervical direction are only faintly recognizable and point to a mostly orthal movement of the lower jaw during the power stroke. The antagonistic facet PR-dl covers the entire distal protocone flank in some specimens of \u003cem\u003eViverra\u003c/em\u003e spp. In the more carnassialized teeth of \u003cem\u003eDinictis\u003c/em\u003e sp., \u003cem\u003eS. venaticus\u003c/em\u003e and \u003cem\u003eF. silvestris\u003c/em\u003e, the facets ed-mb, hld-mb, and PR-dl are missing. As the entoconid and hypoconulid are reduced on the lower carnassial of these taxa, antagonistic structures of the talonid for the protocone of the M1 are missing.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003eProtocone-trigonid-occlusion\u003c/h2\u003e \u003cp\u003eAdditionally, the mesial protocone flank of the M1 occludes with the distal trigonid flank of the m1 in the weakly carnassialized teeth of \u003cem\u003eI. albicauda\u003c/em\u003e and \u003cem\u003eViverra\u003c/em\u003e spp., indicated by the presence of facets md-d and PR-m. In both \u003cem\u003eIchneumia\u003c/em\u003e and \u003cem\u003eViverra\u003c/em\u003e, the mesial protocone flank extends to the base of the paracone, exhibiting an elongated praeprotocrista that forms a cingulum-like structure. In some specimens, facet PACL-m extends in buccal direction from facet PR-m along the praeprotocrista to the base of the paracone along the paracingulum. Facet md-d forms on the distal metaconid flank, running from the apex of the metaconid along the postprotocristid to the notch of the distal trigonid flank. The metaconid is reduced in size or absent in more carnassialized teeth, resulting in a loss of protocone/metaconid occlusion.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eParacone-talonid-occlusion\u003c/h2\u003e \u003cp\u003eFacet hd-mb forms on the mesial flank of the m1 outer buccal margin of the talonid, where it extends along the praehypocristid. The antagonistic structure that occludes with the praehypocristid is the postparacrista of the P4 paracone, where facet PA-dl is present. On the weakly carnassialized teeth of \u003cem\u003eI. albicauda\u003c/em\u003e and \u003cem\u003eViverra\u003c/em\u003e spp., these facets are restricted to the distal paracone flank and the mesial flank of the talonid basin. In the carnassials of \u003cem\u003eDinictis\u003c/em\u003e sp. and \u003cem\u003eS. venaticus\u003c/em\u003e, striations show a steep orientation, running with a slight inclination towards buccal on the mesial hypoconid flank and towards lingual on the distal paracone flank (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). In specimens with further progressed wear, facet hd-mb covers the hypoflexid and connects with facet pr-d on the lower molar, and facet PA-dl wraps around the lingual paracone flank, connecting with facet PA-m on the upper molar (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). The inclination of the striations is parallel to the buccal hypoflexid groove.\u003c/p\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003eParacone-trigonid-occlusion\u003c/h2\u003e \u003cp\u003eOcclusion of the mesial paracone flank of the M1 with the distal trigonid flank of the m1 occurs in all taxa, but a different pattern is observed between weakly and more strongly carnassialized teeth. In \u003cem\u003eI. albicauda\u003c/em\u003e and \u003cem\u003eViverra\u003c/em\u003e spp., facet pr-d forms on the lingual side of the distal m1 trigonid flank. The facet is small and covers only a punctiform area, which also applies for the antagonistic facet PA-m. In the more strongly carnassialized carnassials with a unicuspid talonid (\u003cem\u003eDinictis\u003c/em\u003e sp. and \u003cem\u003eS. venaticus\u003c/em\u003e), facet pr-d covers the entire distal trigonid flank and in some specimens, it extends cervically into the hypoflexid and connects with facet hd-md (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). Occlusion of the mesial paracone flank and the distal trigonid flank appears much more prominent in carnassials with trenchant heel, but it is almost entirely absent in the carnassials of \u003cem\u003eF. silvestris\u003c/em\u003e. On the lower carnassials of \u003cem\u003eF. silvestris\u003c/em\u003e, only a small punctiform facet pr-d is present on the distal trigonid flank, near the apex of the protoconid. An antagonistic punctiform facet PA-m forms on the small M1, where the paracone is reduced to a small cuspule.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003eMetacone-talonid-occlusion\u003c/h2\u003e \u003cp\u003eIn m1, the distal talonid flank forms a U-shaped crest between the hypoconid and the hypoconulid in \u003cem\u003eViverra\u003c/em\u003e spp. and a V-shaped crest with a small notch in \u003cem\u003eI. albicauda\u003c/em\u003e. Along this crest (posthypocristid) extends facet hd-db. A few isolated, weak striations with vertical (cervico-apical) orientation are present. In \u003cem\u003eI. albicauda\u003c/em\u003e, facet hd-db remains small, restricted to the vicinity of the hypoconid apex, with more abundant cervico-apical striations. The distal talonid flank occludes with the mesial metacone flank of the M1. Along the praemetacrista, facet ME-ml is developed, which covers the entire mesial metacone flank in some specimens. The metacone is drastically reduced in size on the more carnassialized M1 of \u003cem\u003eDinictis\u003c/em\u003e sp. and \u003cem\u003eS. venaticus\u003c/em\u003e. The lack of an attritional facet on the metacone as well as the distal talonid flank points to a loss of occlusal contact of these structures. On the M1 of \u003cem\u003eF. silvestris\u003c/em\u003e, the metacone is entirely absent.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eTooth wear in dasyuromorph taxa\u003c/h2\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003eProtocone-talonid-occlusion\u003c/h2\u003e \u003cp\u003eIn the lower molars of \u003cem\u003eD. viverrinus\u003c/em\u003e, facets ed-mb and hld-mb, respectively, form on the mesial flanks of the entoconid and the hypoconulid starting from near the apices. With progressing wear, these facets fuse along the entocristid connecting the entoconid with the hypoconulid and finally form a uniform facet running along the inner disto-lingual margin of the talonid basin. The antagonistic upper molar structure that occludes with the entoconid and the hypoconulid is the distal flank of the protocone. Along the postprotocrista stretches facet PR-dl. Facet PR-dl bears steeply inclined unidirectional striations, running from apical in lingual direction. The areas covered by facets ed-mb and hld-mb on the lower molars and facet PR-dl on the upper molars remain relatively small and are restricted to the proximity of the respective cutting crests. This wear has been observed in the talonid basins of m2 and m3, but was not found on m4. In the more carnassialized teeth of \u003cem\u003eS. harrisii\u003c/em\u003e and \u003cem\u003eT. cynocephalus\u003c/em\u003e, the entoconid and the hypoconulid are reduced and there are no facets indicating occlusion of the talonid with the protocone on any of the lower molars.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eProtocone-trigonid-occlusion\u003c/h2\u003e \u003cp\u003eFacet md-d forms on the lingual side of the distal trigonid blade, extending from the tip of the metaconid along the metacristid. It forms on all lower carnassials of \u003cem\u003eD. viverrinus\u003c/em\u003e. The striations on facet md-d run steeply from apical to buccal. The antagonistic upper molar structure to occlude with the lingual part of the distal trigonid flank is the mesial flank of the protocone, extending from the praeprotocrista. The upper carnassials of \u003cem\u003eD. viverrinus\u003c/em\u003e possess prominent protocones, with facet PR-m forming along the praeprotocrista. On the most distal upper molar of \u003cem\u003eD. viverrinus\u003c/em\u003e (M4), facet PR-m is also present on the mesial protocone flank, indicating that the upper M4 with its reduced crown morphology still occludes with the distal trigonid flank of m4. As the metaconid is largely reduced or lost in the carnassials of \u003cem\u003eS. harrisii\u003c/em\u003e and \u003cem\u003eT. cynocephalus\u003c/em\u003e, there is no antagonistic structure of the trigonid for the protocone to occlude with, resulting in a lack of associated attritional wear.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eParacone-talonid-occlusion\u003c/h2\u003e \u003cp\u003eIn \u003cem\u003eD. viverrinus\u003c/em\u003e, facet hd-mb forms on the mesial flank of the talonid, where it extends from the praehypocristid and eventually covers the entire mesial flank of the talonid. It is present on all lower carnassial teeth, with striations running steeply inclined from apical to buccal. The antagonistic structure to occlude with the praehypocristid is the postparacrista of the upper molars. Along the postparacrista, facet PA-dl forms on the distal flank of the paracone in \u003cem\u003eD. viverrinus\u003c/em\u003e. The striations on facet PA-dl in \u003cem\u003eD. viverrinus\u003c/em\u003e are steeply inclined from apical to buccal. On the distalmost lower molar of \u003cem\u003eD. viverrinus\u003c/em\u003e (m4), facet hd-mb is also present, indicating occlusion with the distalmost upper molar (M4).\u003c/p\u003e \u003cp\u003eIn \u003cem\u003eS. harrisii\u003c/em\u003e and \u003cem\u003eT. cynocephalus\u003c/em\u003e, the prominent hypoflexid of the lower molars is involved into occlusion, where facet hd-mb tends to connect with facet pr-d on the distal trigonid flank with progressing wear. This fusion is most pronounced in the m4 hypoflexid. Facet PA-dl on the upper molars tends to wrap around the lingual paracone flank with progressing wear. Striations cover facets hd-mb and pr-d, which run parallel to the steep hypoflexid inclination and extend into the hypoflexid groove.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eParacone-trigonid-occlusion\u003c/h2\u003e \u003cp\u003eThe distal flank of the trigonid on the lower carnassials of \u003cem\u003eD. viverrinus\u003c/em\u003e forms a cutting blade along the metacristid, with the latter forming a V-shaped crest between the paraconid and the protoconid. Along the buccal half of this crest, facet pr-d extends along the edge from the apex of the paraconid. In lingual direction, it may connect with facet md-d to form one continuous facet, which can cover the entire distal trigonid flank depending on the progression of wear. The facet is present on all lower carnassials of \u003cem\u003eD. viverrinus\u003c/em\u003e, indicating occlusion also with the m4. The antagonistic structure on the upper carnassials is the praeparacrista. Facet PA-m forms along the praeparacrista, covering the mesial flank of the paracone.\u003c/p\u003e \u003cp\u003eOn the derived carnassials of \u003cem\u003eS. harrisii\u003c/em\u003e and \u003cem\u003eT. cynocephalus\u003c/em\u003e, the paracone is reduced in size on M2 and M3 and thus the facet on the mesial paracone flank is either bordering the short praeparacrista, as in \u003cem\u003eS. harrisii\u003c/em\u003e, or is present as a small, punctiform area, as in \u003cem\u003eT. cynocephalus\u003c/em\u003e. On some upper carnassials, a distinctive facet is missing, but unidirectional striations still indicate that attrition may have occurred. The striations on facet PA-m run from apical to lingual, at a steep angle.\u003c/p\u003e \u003cp\u003eThe reduced crown structure of the upper M4 in dasyuromorphs results in a different wear pattern. The paracone is the most prominent cusp on the M4, with the protocone being reduced in size in \u003cem\u003eD. viverrinus\u003c/em\u003e and \u003cem\u003eT. cynocephalus\u003c/em\u003e, and absent in \u003cem\u003eS. sarcophilus\u003c/em\u003e. Facet PA-m on the M4 covers the entire mesial flank of the paracone in these species, indicating that a cutting function is present during occlusion with the lower distal trigonid flank (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). This is confirmed by the presence of facet pr-d on the m4, which cervically extends from the tip of the protoconid to the distal base of the trigonid, covering the hypoflexid groove (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, b).\u003c/p\u003e \u003cp\u003eWith progressing wear, the facet PA-m on M4 extends lingually and wraps around the paracone. This is the result of the hypoflexid moving along the paracone during occlusion. On the m4 of \u003cem\u003eS. harrisii\u003c/em\u003e and \u003cem\u003eT. cynocephalus\u003c/em\u003e, this leads to the formation of a distinctive polished groove on the buccal talonid flank, with striations formed by attrition in the hypoflexid (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, b).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eMetacone-talonid-occlusion\u003c/h2\u003e \u003cp\u003eFacet hd-db forms on the distal flank of the talonid on the lower carnassials of \u003cem\u003eD. viverrinus\u003c/em\u003e, with the exception of m4. It starts forming along the posthypocristid and with progressive wear it extends onto the entire distal talonid flank. The striations on the facet run at a steep inclination from apical to buccal. The posthypocristid occludes with the praemetacrista of the upper molars. Facet ME-ml forms on the mesial flank of the metacone on M2 and M3. On the distalmost upper molar (M4), the metacone is reduced to a vestigial conule, lacking any attritional wear.\u003c/p\u003e \u003cp\u003eIn \u003cem\u003eS. harrisii\u003c/em\u003e and \u003cem\u003eT. cynocephalus\u003c/em\u003e, the rather large metacone occludes with the distal talonid flank, resulting in the formation of facets hd-db on the lower molars and ME-ml on the upper molars. These facets form between M2/m2 and M3/m3, but are absent in M4/m4. The smaller paracone occludes with the mesial talonid flank, forming facets hd-mb on the lower molars and PA-dl on the upper molars. Striations are steeply inclined, pointing to a mostly orthal tooth movement. The reduced metacone morphology seen in the ultimate (M4) of the weakly carnassialized molars of \u003cem\u003eD. viverrinus\u003c/em\u003e is also present in the ultimate locus (M4) of the more strongly carnassialized molars of \u003cem\u003eS. harrisii\u003c/em\u003e and \u003cem\u003eT. cynocephalus\u003c/em\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eOFA analysis of carnivoran taxa\u003c/h2\u003e \u003cp\u003e \u003cb\u003eViverra tangalunga\u003c/b\u003e \u003cb\u003e(weakly carnassialized dentition)\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThe viverrid \u003cem\u003eViverra tangalunga\u003c/em\u003e has a weakly carnassialized carnivoran dentition. For the OFA analysis, specimen SMF 697 was chosen. The m1 talonid and the P4 protocone as well as the post-carnassial molars (M1, M2 and m2) are well developed. The complete power stroke comprises 142 timesteps (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). The initial occlusal contact occurs between the apex of the P4 paracone and the apex of the m1 paraconid, which initiates the first cutting contact between the upper and lower carnassial blades. In timestep 6, a second cutting contact occurs on the lingual side between the apices of the metacone and the protoconid. The occlusal contact between the carnassial blades remains active up until timestep 119. Occlusal contact between the parastyle of M1 and the distal protoconid flank of m1 is also initiated in timestep 6. This area of contact shifts in cervical direction along the distal protoconid flank with further upwards movement of the lower molar and extends into the hypoflexid around timestep 107, whereas it shifts in lingual direction along the praeparacrista towards the paracone apex on M1. In timestep 30, the buccal flank of the protoconid apex of m1 occludes with the postcingulum of P4, which aids in guiding the lower jaw during further upwards movement, as it restricts the freedom of movement. A second point of occlusion on the distal protoconid flank of m1 occurs with the paracingulum of M1 at timestep 32. With further tooth movement it shifts in cervical direction along the same area of the distal protoconid flank that occludes with the parastyle and paracone. The occlusal contacts between M1 and the distal protoconid flank remain active until the point of centric occlusion.\u003c/p\u003e \u003cp\u003eBetween timesteps 99 and 125, occlusal contact between the mesial paracone flank along the\u003c/p\u003e \u003cp\u003epraeparacrista and the distal hypoconid flank along the posthypocristid occurs. In timestep 82,\u003c/p\u003e \u003cp\u003ea first contact occurs between the mesial protocone flank of M1 and the apex of the m1 metaconid. With further tooth movement, this area of contact expands to cover the entire distal\u003c/p\u003e \u003cp\u003emetaconid flank and most of the distal protocone flank up to the point of centric occlusion. Initial occlusal contact in the m1 talonid basin occurs in timestep 121 between the entoconid and the distal M1 protocone flank. This area of contact expands to cover the entire entoconid flank with further tooth movement, and a second occlusal contact between the mesial protocone flank and the hypoconulid is initiated in timestep 126. These contacts remain active up until the point of centric occlusion. Additional contacts during centric occlusion are detected at the apex of the M1 protocone, which occludes into the m1 talonid basin, as well as the tip of the m1 hypoconid, which occludes into the M1 talon basin. Also, small contacts are detected between M2 and m2, respectively in the trigonid and trigon basins of the molars.\u003c/p\u003e \u003cp\u003e \u003cb\u003eSpeothos venaticus\u003c/b\u003e \u003cb\u003e(highly carnassialized dentition with trenchant heel)\u003c/b\u003e\u003c/p\u003e \u003cp\u003eFor the OFA analysis of \u003cem\u003eSpeothos venaticus\u003c/em\u003e, specimen ZFMK MAM 1987\u0026thinsp;\u0026minus;\u0026thinsp;0386 was chosen. The power stroke is comprised of 102 timesteps (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). Initial occlusal contact occurs between the carnassial blades of P4 and m1. It is initially detected between metacone and protoconid and with further upwards movement of the lower jaw a second contact is detected between paracone and metaconid in timestep 6. As the lower molar is moving, these contact areas keep expanding towards the center of the carnassial blades respectively along metacrista and paracristid in direction of the carnassial notches. Around timestep 33, the carnassial notches of P4 and m1 pass each other. Carnassial occlusal contact remains active up until timestep 90. In timestep 13, the first postcarnassial occlusion is detected between the M1 praeparacrista and the distal m1 trigonid flank. With further upwards movement of the lower jaw this contact area shifts in cervical direction along the distal trigonid\u003c/p\u003e \u003cp\u003eflank and expands on the mesial paracone flank. Eventually, this contact area shifts into the hypoflexid groove around timestep 86. An additional contact area at the distal trigonid flank is\u003c/p\u003e \u003cp\u003edetected at timestep 34 with the M1 paracingulum, which occludes with the apex of the protoconid. This contact area also shifts in cervical direction with further tooth movement along\u003c/p\u003e \u003cp\u003ethe distal trigonid flank and remains active up until timestep 94. Initial occlusion between the M1 postparacrista and the m1 praehypocristid is detected at timestep 55. This area of contact\u003c/p\u003e \u003cp\u003eincreases in size with further tooth movement on the mesial hypoconid flank and the distal paracone flank, and eventually shifts into the hypoflexid. Occlusion between hypoflexid and paracone remains active up until the end of the power stroke and is functioning as a guiding contact for the direction of tooth movement. The point of centric occlusion, if it is reached in the dentition of \u003cem\u003eS. speothos\u003c/em\u003e, can only be approximated, as there are no post carnassial crushing contacts, which could function as a stopping mechanism. In the OFA analysis, tooth movement was stopped by occlusion of the tip of the m2 main cusp (protoconid) with the distal protocone flank of M1. It is possible that the in vivo power stroke movement is aborted at an earlier point. The extensive wear that was documented in the hypoflexid shows that the occlusion detected in the OFA analysis up until timestep 94 is realistic.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eOFA analysis of dasyuromorph taxa\u003c/h2\u003e \u003cp\u003e \u003cb\u003eDasyurus viverrinus\u003c/b\u003e \u003cb\u003e(weakly carnassialized dentition)\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThe teeth of specimen SMF 1480 were chosen for the OFA analysis of \u003cem\u003eDasyurus viverrinus\u003c/em\u003e. Centric occlusion is reached at timestep 162 (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). Initial contact occurs between the m4 mesial carnassial blade, at the distal-most point of the paracristid below the paraconid, and the M3 distal blade, at the mesial-most point of the metacrista at the metastyle. With the upwards movement of the lower molar, this area of occlusal contact is expanding lingually and thus the active point of cutting is also moving in lingual direction along the paracristid and the metacrista. Initial contact between the paraconid of m4 and the metacone of M3 occurs at timestep 18. This area of occlusal contact is moving in buccal direction with further upwards movement of the lower molar. Starting with timestep 18, there are two points of active cutting between the paracristid and the metacrista, which are both successively expanding their areas towards the center of the two antagonistic cutting blades. At timestep 19, the initial contact between the metacristid of m3, starting at the protoconid, and the praeparacrista of M3, starting at the parastyle, is calculated. With a further upwards movement of the lower molar, cutting beween the metacristid and the praeparacrista eventually includes the whole mesial paracone flank. First occlusal contact between the paracristid of m3 and the metacrista of M2 is calculated at timestep 24, beginning with the lingual point of contact between the paraconid and the metacone. A second part of contact on the buccal side between protoconid and metastyle is calculated at timestep 30. These two contact areas expand with further upwards movement of the lower molar towards the center of the carnassial blade.\u003c/p\u003e \u003cp\u003eAt timestep 25, initial contact between the metacristid of m4 and the paracrista of M4 is calculated between the apex of the protoconid and the parastyle. This area of occlusal contact successively expands lingually and eventually involves the paracone occluding with the distal carnassial notch. At timestep 96, a second occlusal contact is calculated between the metacristid of m4 and the praeprotocrista of M4, starting with the occlusion of the apices of protocone and metaconid. An additional point of contact between praeprotocrista and metacristid, occurring buccally from the metacristid carnassial notch, is calculated at timestep 109. These two points of cutting between praeprotocrista and metacristid are moving towards the carnassial notch with further upwards movement of the lower molar. The initial occlusal contact between the paracristid of m2, starting at the apex of the protoconid, and the metacrista of M1, starting at the metastyle, is calculated at timestep 73. At timestep 76, a second contact between paracristid and metacrista is calculated, occurring between metacone and paraconid. These two points of occlusal contact are moving towards the center of the carnassial blade with further upwards movement of the lower molar. With this contact, the carnassial blades of m2, m3 and m4 all perform a cutting function while the lower jaw is moving upwards. Initial contact between the metacristid of m2 and the praeparacrista of M2 is calculated at timestep 86. This area of contact expands with further tooth movement towards lingual along the distal paracone flank. A second point of occlusal contact along the metacristid is calculated at timestep 97 and it involves the praeprotocrista. Further upwards movement of the lower jaw results in these two areas of contact moving towards the carnassial notch of the metacristid. The cutting function of m3 metacristid is enhanced by occlusal contact with the praeparacrista of M3 at timestep 102.\u003c/p\u003e \u003cp\u003eThis area of contact on the lingual part of the metacristid is expanding buccally with further tooth movement, while the occlusal contact with the mesial paracone flank expands lingually onto the mesial protocone flank, with both areas expanding towards the carnassial notch of the lower molar. With this contact, the distal trigonid blades of all lower carnassials perform a cutting function during further tooth movement. In addition to the cutting contacts that are calculated at the mesial and distal trigonid flanks, occlusion also occurs on the talonid. At timestep 91, the first contact between the praemetacrista of M3 and the posthypocristid of m3 occurs. Further upwards movement of m2 results in contact between the praemetacrista of M2 and the posthypocristid of m2 at timestep 100. Initial contact between the postparacrista of M3 and the praehypocristid of m3 occurs at timestep 103. A similar contact at timestep 110 occurs between the postparacrista of M2 and the praehypocristid of m2. With further upwards movement of the lower jaw, the protocones of M2, M3 and M4 move into the talonid basins of the antagonistic lower molars. Occlusal contact in the respective talonid basins successively occurs with the occlusion of the buccal entoconid flank and the postprotocrista. This contact occurs between M3 and m3 in timestep 110, between M2 and m2 in timestep 117 and between M4 and m4 in timestep 131. The calculated contact area shifts into the talonid basins of all lower molars and onto the buccal protocone flank of the upper molars with further upwards movement of the lower jaw. This upwards movement is stopped at timestep 162, when the point of centric occlusion is reached.\u003c/p\u003e \u003cp\u003e \u003cb\u003eThylacinus cynocephalus\u003c/b\u003e \u003cb\u003e(highly carnassialized dentition with trenchant heel)\u003c/b\u003e\u003c/p\u003e \u003cp\u003eFor the OFA analysis of \u003cem\u003eThylacinus cynocephalus\u003c/em\u003e, specimen ZMB_Mam_036877 was chosen. The complete chewing path is comprised of 168 steps and consists of one single phase until the point of centric occlusion is reached (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). Initial occlusal contact occurs between the metacrista of M3, starting on the buccal side in proximity to the metastyle, and the distalmost point of the m4 paracristid, in proximity to the apex of the paraconid. With further upwards movement of the lower molars, this contact area expands in mesial direction towards the carnassial notch of m4 and in direction of the metacone of M3. In timestep 18 the first contact between the M3 metacone and the m4 protoconid occurs, marking a second point of occlusion between the M3 and m4 carnassial blades. Both contact areas keep expanding on the occluding flanks and approach each other with further tooth movement, eventually wrapping around the carnassial notch of the lower molar and fusing in timestep 58. In timestep 31, occlusal contact occurs between the mesial paracone flank of M3 and the distal trigonid flank of m3. With further tooth movement, this contact area expands along the praeparacrista and postparacrista of M3 and along the distal trigonid flank of m3 in cervical direction. This occlusal contact remains up until timestep 120. In timestep 61, two points of contact between the carnassial blades of M2 and m3 are detected. The first occurs on the buccal side, in proximity to the metastyle and the protoconid. The second contact occurs on the lingual side, in proximity to the metacone and the paraconid. Both contacts expand with further tooth movement, approximating each other along the metacrista and the paracristid. Eventually, they wrap around the carnassial notch of m3 and fuse in timestep 99. First contact between the mesial paracone flank of M2 and the distal trigonid blade of m2 occurs in timestep 62. With further tooth movement, the area of occlusal contact expands along the postparacrista and the praepacacrista of M2 and expands in cervical direction of both antagonistic flanks and remains up until timestep 127. In timestep 86, the first occlusal contact between the carnassial blades of M1 and m2 is detected. It occurs on the buccal side of the blades between the metastyle of M1 and the protoconid of m2. With further upwards movement of the lower molars, this contact area expands in lingual direction along the metacrista and the paracristid. A second point of contact on the lingual side is detected in timestep 97. It occurs between the metacone of M1 and the paraconid of m2. With further tooth movement, this contact expands in lingual direction. Both areas of contact approximate each other in the following timesteps and merge in timestep 118, wrapping around the carnassial notch of the lower molar. The first contact between the mesial paracone flank of M4 and the distal trigonid flank of m4 occurs in timestep 53. This contact remains during most of the rest of the chewing path, with the distal trigonid flank of m4 occluding along the paracone of M4 up until 15 timesteps before centric occlusion. Eventually, the contact wraps around the paracone and covers the hypoflexid. In addition to the trigonids occluding with the paracones and metacones, there are occlusal contacts between the talonids and the paracones and metacones. The first contact occurs in timestep 63 between the distal talonid flank of m3 and the mesial metacone flank of M3. It starts on the lingual side, along the praemetacrista in proximity to me metacone and along the posthypocristid in proximity to the hypoconulid. With further tooth movement, this occlusal contact expands in buccal direction along the praemetacrista and along the posthypocristid towards the hypocone. This occlusion remains until timestep 112. In timestep 100, the first occlusal contact between the distal paracone flank of M3 and the mesial talonid flank of m3 is detected. This contact area remains small and is only active for a shorter duration, up until timestep 136. The first occlusal contact between the distal talonid flank of m2 and the mesial metacone flank of M2 occurs in timestep 107 on the lingual side. The area of contact expands with further tooth movement along the praemetacrista in lingual direction from the metacone and from the hypoconulid towards the hypoconid. It remains active until timestep 131.The mesial talonid flank of m2 occludes with the distal paracone flank of M2 first in timestep 133. The area of contact remains small and is active until timestep 155.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe documented tooth wear as well as the OFA analysis both point to an emphasized shearing function of the unicuspid talonid in carnivoran and dasyuromorph carnassials, with a subordinate guiding component. The lingual cusps of the upper carnassials (paracone\u0026thinsp;+\u0026thinsp;metacone or metastyle) and the connecting crests are aligned longitudinally from mesial to distal, to increase the shearing function. Occlusion occurs between the carnassial blades and between the distal paracone and mesial talonid flank. The crown structure of the lower carnassials remains more conservative in carnivorans and dasyuromorphs, while more apomorphic adaptations are present in the upper dentition. Differences in the crown morphology of the upper teeth in return result in some occlusal differences between carnivorans and dasyuromorphs. In marsupials, which have multiple carnassial teeth, additional occlusion occurs between the mesial metacone flank and the distal talonid flank (except for the last lower carnassial, which lacks a distal upper antagonist). Occlusal contact between the buccal protocone flank and the lingual hypoconid flank is generally reduced in carnassials with unicuspid talonids, indicating loss of the crushing function. For \u003cem\u003eThylacinus cynocephalus\u003c/em\u003e a short period of occlusion between protocone and hypoconid was calculated at the end of the power stroke in the OFA reconstruction, which then acts as a terminal \u0026ldquo;stopping\u0026rdquo; point for the tooth movement. The reduction of two talonid cusps (entoconid and hypoconulid) and loss of the basined talonid in carnassials allows an enlargement of the mesial talonid (hypoconid) flank and thus the opening of the hypoflexid groove, which connects to the distal trigonid flank. As a result, the shearing function of the trenchant talonid is enhanced. In carnassial teeth with tricuspid talonids, as in \u003cem\u003eDasyurus viverrinus\u003c/em\u003e, \u003cem\u003eIchneumia albicauda\u003c/em\u003e, \u003cem\u003eViverra tangalunga\u003c/em\u003e and \u003cem\u003eViverra zibetha\u003c/em\u003e, and the presence of multiple facets within the talonid basin points to a stronger emphasis on a crushing function, while the paracone/hypoflexid function is only weakly pronounced. The OFA reconstructions also revealed a functional difference, with a shorter paracone/hypoflexid occlusal contact before centric occlusion in \u003cem\u003eDasyurus viverrinus\u003c/em\u003e (27% of timesteps) and \u003cem\u003eViverra tangalunga\u003c/em\u003e (12%) than in \u003cem\u003eSpeothos venaticus\u003c/em\u003e (46%) and \u003cem\u003eThylacinus cynocephalus\u003c/em\u003e (35%). In all taxa, steeply lingually inclined striations on the facets indicate a mostly orthal tooth movement during the power stroke, to which the paracone/hypoflexid occlusion contributes in the strongly carnassialized condition with a trenchant heel.\u003c/p\u003e \u003cp\u003eSol\u0026eacute; \u0026amp; Ladev\u0026egrave;ze (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) postulated a cusp reduction in carnassials in reverse sequence of the patterning cascade mode of cusp development as formulated by Jernvall (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1995\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2000\u003c/span\u003e) and Jernvall and Jung (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2000\u003c/span\u003e), although a decoupling of metaconid and talonid development in carnassials is noted. Further, the resemblance of carnassials to the molariforms of mammaliaforms and early mammals, especially the morganucodontans and eutriconodontans, due to the linear alignment of cusps and absence of a triangular tooth crown, is noted (Sol\u0026eacute; \u0026amp; Ladev\u0026egrave;ze \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The reuse of the hypoflexid groove for shear-cutting in carnassials apparently is linked to the sequential reduction of cusps (with the hypoconid being the last cusp to get reduced). Cusp d of the triconodont teeth of morganucodontans, generally regarded as a the initial talonid cusp, did not perform a major cutting function. J\u0026auml;ger et al. (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) showed occlusal relationships in triconodont teeth of \u003cem\u003eMorganucodon\u003c/em\u003e and \u003cem\u003eMegazostrodon\u003c/em\u003e which differ from those seen in carnassials, with the mesial flank of cusp C (metacone) occluding with cusp d (hypoconid). The main piercing and cutting function are performed by cusp A (paracone), as it is the main cusp of the upper molar. Cusp A occludes with the mesial flank of cusp c (metaconid), and not with cusp d (J\u0026auml;ger et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Occlusion of cusp A and cusp d is established later in mammalian evolution, after triangulation of the trigon and trigonid cusps. At this point the occlusal relationships become comparable to those of carnassial teeth with a unicuspid talonid, where cusp A (paracone) is occluding between the unicuspid talonid cusp and cusp a (protoconid). Thus, a groove exhibiting functional resemblance to the hypoflexid of the tribosphenic molar (and its derivatives) is present in morganucodontan teeth. Whether the presence of the hypoflexid groove in carnassials is a result of the reduction of cusps based on the patterning cascade mode, suggesting structural homology, remains ambiguous, as the identity of the first talonid cusp to evolve (hypoconid or hypoconulid) is debated (Davis \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Eutriconodontan molars are another good functional equivalent to carnassials, as they also emphasize the cutting function, with cusp d increasing in size and being integrated in the cutting function (J\u0026auml;ger et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). In some late surviving morganucodontans from the Upper Jurassic, cusp c is enlarged, as seen in \u003cem\u003eStorchodon cingulatus\u003c/em\u003e (Martin et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). This results in a lower molar morphology that is strikingly similar to lower carnassials with a unicuspid talonid. In these teeth, a groove forms between cusps a and c, which structurally resembles the hypoflexid groove of carnassials with unicuspid talonid. The structural resemblance between carnassial teeth and triconodont teeth, where the cusps are aligned along the longitudinal axis, is the result of the functional requirements of a meat-cutting dentition, which favors longitudinally aligned cutting blades. The pronounced hypoflexid groove in carnassial teeth provides an additional shearing locus between the paracone and the unicuspid talonid, which is further enhanced by the more simplified talonid morphology of highly carnassialized teeth (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). It is interesting to note that in all investigated taxa which exhibit a carnassial with unicuspid talonid, a small notch is present between the hypoconid and the distal trigonid flank. This notch increases the cutting efficiency, as it duplicates the function of the main carnassial notch at a smaller scale.\u003c/p\u003e \u003cp\u003eThe striations on the facets associated with the paracone/hypoflexid occlusion of the carnassials show a uniform orientation. They indicate that the slightly obliquely inclined tooth movement, as initiated with carnassial blade occlusion, is maintained during the power stroke. This function is comparable to some extent to the hypoflexid function in cladotherian dryolestidans, although the guiding component is more pronounced in these pretribosphenic teeth than in the carnassials (Schultz \u0026amp; Martin \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). A change of the inclination of the striations on the distal trigonid flank near the hypoflexid, as observed in dryolestidan molars (Schultz \u0026amp; Martin \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), was not observed in the hypoflexids of carnassial teeth. Thus, a crushing component, which would result in a change of striation inclination, cannot be inferred for the carnassial trenchant heel. The guiding function of paracone/hypoflexid occlusion in carnassials can be attributed to the effect of \u0026ldquo;autocclusion\u0026rdquo;, a term that has been coined to refer to the occlusal alignment of cusps during tooth movement being controlled by the morphology of the teeth (Mellett, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1985\u003c/span\u003e). Autocclusion limits the neurological requirements for tooth alignment to the initial occlusal contact of the power stroke (Evans \u0026amp; Sanson, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2006\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe development of a trenchant unicuspid talonid with a shearing hypoflexid evolved multiple times from the tribosphenic pattern in therians with carnassial adaptations, resulting in similar occlusal patterns, indicating an increase in faunivory. The therian carnassials with pronounced hypoflexid exhibit a remarkable structural resemblance to molariforms of non-tribosphenic mammaliaforms and mammals, such as morganucodontans and eutriconodontans, as well as pretribosphenic dryolestidans. Due to their small body size, morganucodontans and dryolestidans relied on an insectivorous and invertebrate diet (Gill et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Schultz \u0026amp; Martin, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Some eutriconodontans, however, reached larger body sizes, such as \u003cem\u003eRepenomamus giganticus\u003c/em\u003e with an estimated body mass of 12\u0026ndash;14 kg (Hu et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2005\u003c/span\u003e), representing the largest known Mesozoic mammal. \u003cem\u003eRepenomamus\u003c/em\u003e and other large-bodied eutriconodontans such as \u003cem\u003eGobiconodon\u003c/em\u003e were predators and/or scavengers, antedating the therian carnivorous adaptation at the non-tribosphenic level. In therians, the carnassialization of the molars was acquired by a reduction of the tribosphenic pattern, functionally getting back to the pretribosphenic condition.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe thank Julia Schultz (Bonn) for the provision of scan data of \u003cem\u003eD. leiriensis\u003c/em\u003e. For the loaning of specimens, we thank Lo\u0026iuml;c Costeur (NMB), Jan Decher (ZFMK), Eberhard (Dino) Frey (formerly SMNK), Christiane Funk (ZMB), J\u0026ouml;rn K\u0026ouml;hler (HLMD), Katrin Krohmann (SMF), Frieder Mayer (ZMB) and Irina Ruf (SMF, Senckenberg Gesellschaft f\u0026uuml;r Naturforschung). This research was funded by a doctoral grant to A. J. Lang by the Studienstiftung des deutschen Volkes. Open access funding enabled and organized by project DEAL.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBoth authors contributed to the study conception and design. Casting, tooth wear documentation, scanning and OFA analyses were performed by AJL. The first draft of the manuscript was written by AJL. AJL and TM contributed critically to previous versions of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was funded by a doctoral grant to A. J. Lang by the Studienstiftung des deutschen Volkes.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSupplementary materials including the OFA project files used in this study are available in the figshare repository, https://doi.org/10.6084/m9.figshare.26067505. Scan data of the specimens used in the OFA analyses is available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBenazzi S, Kullmer O, Grosse IR, Weber GW (2011) Using occlusal wear information and finite element analysis to investigate stress distributions in human molars. J Anat 219(3):259\u0026ndash;72. https://doi.org/10.1111/j.1469-7580.2011.01396.x\u003c/li\u003e\n\u003cli\u003eButler PM. 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Comptes Rendus de l\u0026apos;Acad\u0026eacute;mie des Sciences - Series IIA - Earth and Planetary Science 330(9):653\u0026ndash;658. https://doi.org/10.1016/S1251-8050(00)00199-3\u003c/li\u003e\n\u003cli\u003eSchultz JA, Martin T (2011) Wear pattern and functional morphology of dryolestoid molars (Mammalia, Cladotheria). Pal\u0026auml;ontol Z 85:269\u0026ndash;285. https://doi.org/10.1007/s12542-010-0091-8\u003c/li\u003e\n\u003cli\u003eSchultz JA, Martin T (2014) Function of pretribosphenic and tribosphenic mammalian molars inferred from 3D animation. Naturwissenschaften 101:771\u0026ndash;781. https://doi.org/10.1007/s00114-014-1214-y\u003c/li\u003e\n\u003cli\u003eSchultz JA, Menz U, Winkler DE, Schulz-Kornas E, Engels S, Kalthoff DC, von Koenigswald W, Ruf I, Kaiser TM, Kullmer O, S\u0026uuml;dekum KH, Martin T (2017) Modular Wear Facet Nomenclature for mammalian post-canine dentitions. Historical Biology 30(1\u0026ndash;2):30\u0026ndash;41. https://doi.org/10.1080/08912963.2017.1302442\u003c/li\u003e\n\u003cli\u003eSol\u0026eacute;, F, Ladev\u0026egrave;ze S (2017) Evolution of the hypercarnivorous dentition in mammals (Metatheria, Eutheria) and its bearing on the development of tribosphenic molars. Evolution \u0026amp; Development 19:56\u0026ndash;68. https://doi.org/10.1111/ede.12219\u003c/li\u003e\n\u003cli\u003eTarquini SD, Chemisquy MA, Prevosti FJ (2020) Evolution of the carnassial in living mammalian carnivores (Carnivora, Didelphimorphia, Dasyuromorphia): Diet, phylogeny, and allometry. Journal of Mammalian Evolution 27:95\u0026ndash;109. https://doi.org/10.1007/s10914-018-9448-7\u003c/li\u003e\n\u003cli\u003eThenius E (1989) Tlbd/Part 56 Z\u0026auml;hne und Gebi\u0026szlig; der S\u0026auml;ugetiere. De Gruyter, Berlin, Boston. https://doi.org/10.1515/9783110856927\u003c/li\u003e\n\u003cli\u003eVan Valkenburgh B (1991) Iterative Evolution of Hypercarnivory in Canids (Mammalia: Carnivora): Evolutionary Interactions Among Sympatric Predators. Paleobiology 17(4):340\u0026ndash;362. https://doi.org/10.1017/S0094837300010691\u003c/li\u003e\n\u003cli\u003eVan Valkenburgh B (2007) D\u0026eacute;j\u0026agrave; vu: the evolution of feeding morphologies in the Carnivora. Integrative and Comparative Biology 47:147\u0026ndash;163. https://doi.org/10.1093/icb/icm016\u003c/li\u003e\n\u003cli\u003eVan Valkenburgh B, Wayne RK (2010) Carnivores. Curr Biol 20(21):R915\u0026ndash;919. https://doi.org/10.1016/j.cub.2010.09.013\u003c/li\u003e\n\u003cli\u003eWortman JL, Matthew WD (1899). The ancestry of certain members of the Canidae, the Viverridae, and Procyonidae. Bulletin of the American Museum of Natural History 12:109\u0026ndash;38. http://hdl.handle.net/2246/1535\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":"mammal-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"acth","sideBox":"Learn more about [Mammal Research](http://link.springer.com/journal/13364)","snPcode":"13364","submissionUrl":"https://www.editorialmanager.com/acth/default2.aspx","title":"Mammal Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Carnassials, Carnivora, Dasyuromorphia, Odontology, Functional morphology, Dental wear","lastPublishedDoi":"10.21203/rs.3.rs-4610245/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4610245/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe carnassial teeth of Carnivora and Dasyuromorphia are characterized by the enlargement of the carnassial blades and reduction of crushing structures. In some species, the highly carnassialized teeth exhibit a unicuspid talonid with only the hypoconid present (\u0026ldquo;trenchant heel\u0026rdquo;). This condition is similar to that seen in the molars of pretribosphenic cladotherians such as Dryolestida, with a single talonid cusp and hypoflexid groove. Tooth wear and reconstruction of the power stroke show that the hypoflexid of the trenchant heel occludes with the paracone of the distal upper antagonist, providing a cutting and guiding function during the power stroke, and maintaining a uniform inclination of the tooth movement up to the point of centric occlusion. In case of the Dasyuromorphia, this occlusal relationship is most pronounced between the distal molars (M4/m4), whereas in the Carnivora it occurs between the upper and lower mesial molars (M1/m1). The occurrence of distal hypoflexid-like grooves is a recurring trend in mammal evolution, before and after the evolution of tribosphenic molars with multicuspid talonid.\u003c/p\u003e","manuscriptTitle":"Hypoflexid function in the “trenchant heel” of carnassial teeth, with comments on talonid evolution","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-18 22:26:16","doi":"10.21203/rs.3.rs-4610245/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2024-06-29T02:59:00+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-06-24T11:50:10+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-06-21T12:59:14+00:00","index":"","fulltext":""},{"type":"submitted","content":"Mammal Research","date":"2024-06-21T04:58:11+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"mammal-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"acth","sideBox":"Learn more about [Mammal Research](http://link.springer.com/journal/13364)","snPcode":"13364","submissionUrl":"https://www.editorialmanager.com/acth/default2.aspx","title":"Mammal Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"186f8925-c95c-48a1-bf47-e4b0485559d6","owner":[],"postedDate":"July 18th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-09-16T16:08:55+00:00","versionOfRecord":{"articleIdentity":"rs-4610245","link":"https://doi.org/10.1007/s13364-024-00762-1","journal":{"identity":"mammal-research","isVorOnly":false,"title":"Mammal Research"},"publishedOn":"2024-09-09 15:57:44","publishedOnDateReadable":"September 9th, 2024"},"versionCreatedAt":"2024-07-18 22:26:16","video":"","vorDoi":"10.1007/s13364-024-00762-1","vorDoiUrl":"https://doi.org/10.1007/s13364-024-00762-1","workflowStages":[]},"version":"v1","identity":"rs-4610245","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4610245","identity":"rs-4610245","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}