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

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.

Full text

ORIGINAL ARTICLE
Mammal Research
https://doi.org/10.1007/s13364-024-00762-1
morphology which emphasizes the postvallum/prevallid
slicing function and reduces the protocone/talonid crushing
function (De Muizon and Lange-Badré 1997).
The Carnivora are the most diverse extant clade of car-
nivorous 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-car-
nassial crushing part of the dentition (Van Valkenburgh and
Wayne 2010). Some extant species of the marsupial Didel-
phimorphia and Dasyuromorphia also evolved carnassial
teeth, with the upper M1-M3 and the lower m2-m4 forming
three pairs of carnassials (Tarquini et al. 2020). The distal-
most carnassials in marsupials (M3/m4) are the “principal
carnassials”, exhibiting the most carnassialized condition of
the tooth row (Butler 1946; Tarquini et al. 2020; Lang et al.
2022). Generally, the carnassials of carnivorans and mar-
supials exhibit similar structural modications, 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 and Ladevèze 2017).
The grade of talonid reduction in carnassialized teeth var-
ies between taxa. The carnassials of canids retain a basined
talonid which performs a crushing function, although the
Introduction
Carnassial teeth, specialized for the slicing of meat, evolved
convergently among carnivorous mammals, i.e. the Car-
nivora, Hyaenodonta, Oxyaenodonta and Dasyuromorphia
(De Muizon and Lange-Badré 1997; Van Valkenburgh
2007; Tarquini et al. 2020). Generally, carnassials are char-
acterized by a secondary reduction of features seen in tri-
bosphenic 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 & Hiimäe 1969; Crompton & Hiimäe 1970; Luo
2007). With increasing carnassialization, the protocone of
the upper carnassial and the metaconid and talonid cusps
(entoconid, hypoconid and hypoconulid) of the lower car-
nassial are reduced (Lang et al. 2022). This results in a
Communicated by Jan M. Wójcik.
Andreas Johann Lang
ajlang@gmx.de
1 Section Palaeontology, Bonn Institute of Organismic
Biology, Rheinische Friedrich-Wilhelms-Universität Bonn,
Nussallee 8, Bonn 53115, Germany
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 cladotheri-
ans such as Dryolestida, with a single talonid cusp and hypoexid groove. Tooth wear and reconstruction of the power
stroke show that the hypoexid 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 hypoexid-like grooves is a recurring trend in mammal evolution, before and after the evolution of
tribosphenic molars with multicuspid talonid.
Keywords Carnassials · Carnivora · Dasyuromorphia · Odontology · Functional morphology · Dental wear
Received: 21 June 2024 / Accepted: 3 September 2024
© The Author(s) 2024
Hypoexid function in the “trenchant heel” of carnassial teeth, with
comments on talonid evolution
Andreas JohannLang1· ThomasMartin1
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hypoconulid is reduced in some species such as Canis lupus
(Berkovitz and Shellis 2018). In the most extreme carnassi-
alized 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 and Matthew 1899). The trenchant heel is
usually interpreted to serve as a secondary cutting feature,
with the enlarged single talonid cusp (hypoconid) function-
ing as an additional cutting blade (Van Valkenburgh 1991).
Carnassials with a unicuspid trenchant talonid evolved mul-
tiple times within the Carnivora. Among extant Caniformia,
it is present in Cuon alpinus, Lycaon pictus, and Speothos
venaticus (Berkovitz and Shellis 2018). Within the Felifor-
mia, it evolved in the extinct Nimravidae (e.g. Nimravus)
(Peigné 2000). In the carnassials of the marsupial Dasyuro-
morphia, a reduced unicuspid talonid evolved in Sarcophi-
lus 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 car-
nassial crown structure towards the pretribosphenic condi-
tion. 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 and
Ladevèze 2017). This inferred resemblance is purely based
on morphological similarities, while a functional compari-
son 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 ank are separated by
a deep hypoexid 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 and Martin 2011). In more derived tri-
bosphenic molars, the hypoexid is reduced and has lost the
guiding function. Crushing is instead performed by occlu-
sion of the upper molar protocone into the talonid basin
(Schultz and Martin 2014). The observed structural simi-
larities between the unicuspid talonids of carnassial and pre-
tribosphenic teeth (Fig. 1) suggest an analogous function.
While tooth function of the mammaliaform Morganu-
codonta relied mostly on puncturing and shearing and less
so on precise cutting, eutriconodontans involved all seri-
ally 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 tribos-
phenic molar is debated (Davis 2011).
There is a structural resemblance between pretribos-
phenic molars and carnassial teeth with a trenchant heel,
both exhibiting a reduced morphology of the tribosphenic
condition with multicuspid talonid. This raises the ques-
tion, if there occurred a functional shift in carnassials with
trenchant heel, with a replacement of the protocone/talonid
occlusion by a paracone/hypoexid occlusion, similar to the
situation in pretribosphenic molars.
The objective of this study is to elucidate the functional
role of the hypoexid groove in carnassial teeth with tren-
chant heel and in which aspects the trenchant heel is func-
tionally comparable to the distal portion of non-tribosphenic
(cusp c + d) and pretribosphenic (cusp d [hypoconulid])
teeth.
Methods
Nine species with dierent degrees of carnassialization
were studied (list of specimens in Online Resource 1).
These include six carnivoran species, with Ichneumia albi-
cauda, Viverra tangalunga and Viverra zibetha representing
a weakly carnassialized condition with a tricuspid talonid,
Speothos venaticus and Dinictis sp. representing the car-
nassial 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 Sar-
cophilus 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 pol-
ished 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). Map-
ping of the facets can be used to determine complementary
occlusal crown structures and compare the function of dif-
ferent teeth during the power stroke, which is the section
of the chewing movement during which occlusal contact
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occurs (Crompton 1971; Schultz et al. 2017). For facets
(Fig. 2), 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 Organ-
ismic 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
100,023 and NLMH 105,654, described in Martin et al.
(2019, 2024), were used. For segmentation, the software
Avizo 8 (Thermo Fisher Scientic, 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 (V. tangalunga
[Online Resource 2] and Speothos [Online Resource 3]) and
two dasyuromorphs (Dasyurus [Online Resource 4] and
Tylacinus [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 Dasyuromor-
phia) 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
Fig. 1 The carnassialized and postcarnassial teeth of Speothos venati-
cus (P4, M1, m1) and Thylacinus cynocephalus (M3, M4, m4) in
comparison to upper and lower molars of the non-tribosphenic mor-
ganucodontid Storchodon cingulatus and of the pre-tribosphenic
cladotherian Dryolestes leiriensis. Blue arrows indicate the presence
of a hypoexid or hypoexid-like groove on the lower molars. Upper
molars are depicted in occlusal view. Lower molars are depicted in
buccal, occlusal and lingual view (from top to bottom) with occlusal
and lingual views being mirrored in respect to buccal view
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50,000 triangles before the analysis using the mesh opti-
mization tool of PolyWorks. Antagonistic tooth rows were
positioned in centric occlusion, which is the point of maxi-
mum intercuspation sensu Crompton and Hiiemäe (1970),
using the manual alignment tools of PolyWorks. In tribos-
phenic 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 quantied and that indicate the chewing move-
ments. The directions of the preliminary stroke and the
recovery stroke sensu Crompton and Hiiemäe (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 hypoexid occlusion. The size of the area of occlusal
contact per timestep was visualized by contact diagrams.
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
Table 1 List of abbreviations for crown structures, positions of facets
and institutions
Abbreviations for crown structures of mammalian molars
(modied after Schultz et al.2017)
ed Entoconid
hd Hypoconid
hld Hypoconulid
MEC Metacrista
ME Metacone
md Metaconid
MTS Metastyle
PACL Paracingulum
PA Paracone
p.a. 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 Labora-
tory 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 (MfN), Humboldt-
Universität zu Berlin, Germany
Fig. 2 Facets on a lower m3 of Dasyurus viverrinus, using the terminology after Schultz et al. (2017)
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Felis, 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 tal-
onid for the protocone of the M1 are missing.
Protocone-trigonid-occlusion
Additionally, the mesial protocone ank of the M1 occludes
with the distal trigonid ank of the m1 in the weakly car-
nassialized teeth of Ichneumia and Viverra spp., indicated
by the presence of facets md-d and PR-m. In both Ichneu-
mia and Viverra spp., the mesial protocone ank extends to
the base of the paracone, exhibiting an elongated praeprot-
ocrista that forms a cingulum-like structure. In some speci-
mens, 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 ank, running from the apex of the metaconid
along the postprotocristid to the notch of the distal trigonid
ank. The metaconid is reduced in size or absent in more
carnassialized teeth, resulting in a loss of protocone/meta-
conid occlusion.
Paracone-talonid-occlusion
Facet hd-mb forms on the mesial ank of the m1 outer buc-
cal margin of the talonid, where it extends along the prae-
hypocristid. The antagonistic structure that occludes with
the praehypocristid is the postparacrista of the P4 paracone,
where facet PA-dl is present. On the weakly carnassial-
ized teeth of Ichneumia and Viverra spp., these facets are
restricted to the distal paracone ank and the mesial ank of
the talonid basin. In the carnassials of Dinictis and Speothos,
striations show a steep orientation, running with a slight
inclination towards buccal on the mesial hypoconid ank
and towards lingual on the distal paracone ank (Fig. 3a,
c). In specimens with further progressed wear, facet hd-mb
covers the hypoexid and connects with facet pr-d on the
lower molar, and facet PA-dl wraps around the lingual para-
cone ank, connecting with facet PA-m on the upper molar
(Fig. 3b, d). The inclination of the striations is parallel to the
buccal hypoexid groove.
Paracone-trigonid-occlusion
Occlusion of the mesial paracone ank of the M1 with the
distal trigonid ank of the m1 occurs in all taxa, but a dier-
ent pattern is observed between weakly and more strongly
carnassialized teeth. In Ichneumia and Viverra spp., facet
pr-d forms on the lingual side of the distal m1 trigonid ank.
The facet is small and covers only a punctiform area, which
also applies for the antagonistic facet PA-m. In the more
carnassial blade between the paraconid and the protoconid.
On the weakly carnassialized teeth of Ichneumia albicauda,
Viverra tangalunga, Viverra zibetha and Dasyurus viverri-
nus, the hypoconid is the most prominent cusp of the tal-
onid, with the hypoconulid and the entoconid being smaller.
In more strongly carnassialized teeth, the metaconid is
reduced (as in Speothos venaticus and Sacrophilus harri-
sii) 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 dasy-
uromorphs dier in the construction of the carnassial blade.
As the blade extends between the metacone and the para-
cone in carnivorans, the paracone is the only lingual cusp
besides the small protocone, which gets reduced in more
strongly carnassialized teeth (e.g. Felis silvestris). In con-
trast 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 Sarcophilus and Thylacinus). 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 meta-
cone 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 pat-
tern is seen in the weakly carnassialized teeth of Ichneumia,
V. tangalunga and V. zibetha as well as the higher carnassial-
ized teeth of Dinictis and Speothos.
Tooth wear in carnivoran taxa
Protocone-talonid-occlusion
In the weakly carnassialized teeth of Ichneumia, V. tanga-
lunga 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 ank of the M1 with
the mesial anks of entoconid and hypoconulid of the m1
is indicated by the presence of facets ed-mb, hld-mb and
PR-dl. The mesial anks of the entoconid and the hypoco-
nulid appear polished in Ichneumia and Viverra spp., indi-
cating 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 ank in some specimens of Viverra spp.
In the more carnassialized teeth of Dinictis, Speothos and
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Along this crest (posthypocristid) extends facet hd-db. A
few isolated, weak striations with vertical (cervico-apical)
orientation are present. In Ichneumia, facet hd-db remains
small, restricted to the vicinity of the hypoconid apex, with
more abundant cervico-apical striations. The distal talonid
ank occludes with the mesial metacone ank of the M1.
Along the praemetacrista, facet ME-ml is developed, which
covers the entire mesial metacone ank in some specimens.
The metacone is drastically reduced in size on the more
carnassialized M1 of Dinictis and Speothos. The lack of an
attritional facet on the metacone as well as the distal talonid
ank points to a loss of occlusal contact of these structures.
On the M1 of Felis, the metacone is entirely absent.
strongly carnassialized carnassials with a unicuspid talonid
(Dinictis and Speothos), facet pr-d covers the entire distal
trigonid ank and in some specimens, it extends cervically
into the hypoexid and connects with facet hd-md (Fig. 3a,
c). Occlusion of the mesial paracone ank and the distal
trigonid ank appears much more prominent in carnassials
with trenchant heel, but it is almost entirely absent in the
carnassials of Felis. On the lower carnassials of Felis, only
a small punctiform facet pr-d is present on the distal trigo-
nid ank, 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 ank forms a U-shaped crest
between the hypoconid and the hypoconulid in Viverra
spp. and a V-shaped crest with a small notch in Ichneumia.
Fig. 3 Tooth wear on the m1 (a) and M1 (b) of Dinictis sp. (SMNK-PAL 9090) and on the m1 (c) and M1 (d) of Speothos venaticus (ZFMK MAM
1992.0565). Dashed lines mark the visible edges of facets. Solid lines indicate the inclination of striations. Photographs of epoxy casts
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occlude with the praehypocristid is the postparacrista of the
upper molars. Along the postparacrista, facet PA-dl forms
on the distal ank of the paracone in Dasyurus. The stria-
tions on facet PA-dl in Dasyurus are steeply inclined from
apical to buccal. On the distalmost lower molar of Dasyurus
(m4), facet hd-mb is also present, indicating occlusion with
the distalmost upper molar (M4).
In Sarcophilus and Thylacinus, the prominent hypoexid
of the lower molars is involved into occlusion, where facet
hd-mb tends to connect with facet pr-d on the distal trigonid
ank with progressing wear. This fusion is most pronounced
in the m4 hypoexid. Facet PA-dl on the upper molars tends
to wrap around the lingual paracone ank with progressing
wear. Striations cover facets hd-mb and pr-d, which run par-
allel to the steep hypoexid inclination and extend into the
hypoexid groove.
Paracone-trigonid-occlusion
The distal ank of the trigonid on the lower carnassials of
Dasyurus 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 tri-
gonid ank depending on the progression of wear. The facet
is present on all lower carnassials of Dasyurus, indicat-
ing 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 ank of
the paracone.
On the derived carnassials of Sarciphilus and Thylaci-
nus, the paracone is reduced in size on M2 and M3 and thus
the facet on the mesial paracone ank is either bordering
the short praeparacrista, as in Sarcophilus, or is present as
a small, punctiform area, as in Thylacinus. 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 dasy-
uromorphs results in a dierent wear pattern. The paracone
is the most prominent cusp on the M4, with the protocone
being reduced in size in Dasyurus and Thylacinus, and
absent in Sarcophilus. Facet PA-m on the M4 covers the
entire mesial ank of the paracone in these species, indicat-
ing that a cutting function is present during occlusion with
the lower distal trigonid ank (Fig. 4b, d). This is conrmed
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 hypoexid groove (Fig. 4a, b).
Tooth wear in dasyuromorph taxa
Protocone-talonid-occlusion
In the lower molars of Dasyurus, facets ed-mb and hld-mb,
respectively, form on the mesial anks of the entoconid and
the hypoconulid starting from near the apices. With pro-
gressing wear, these facets fuse along the entocristid con-
necting the entoconid with the hypoconulid and nally 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 ank 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 Sarcophilus and Thy-
lacinus, 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 Dasyurus.
The striations on facet md-d run steeply from apical to buc-
cal. The antagonistic upper molar structure to occlude with
the lingual part of the distal trigonid ank is the mesial ank
of the protocone, extending from the praeprotocrista. The
upper carnassials of Dasyurus possess prominent proto-
cones, with facet PR-m forming along the praeprotocrista.
On the most distal upper molar of Dasyurus (M4), facet
PR-m is also present on the mesial protocone ank, indicat-
ing that the upper M4 with its reduced crown morphology
still occludes with the distal trigonid ank of m4. As the
metaconid is largely reduced or lost in the carnassials of
Sarciphilus and Thylacinus, there is no antagonistic struc-
ture of the trigonid for the protocone to occlude with, result-
ing in a lack of associated attritional wear.
Paracone-talonid-occlusion
In Dasyurus, facet hd-mb forms on the mesial ank of the tal-
onid, where it extends from the praehypocristid and eventu-
ally covers the entire mesial ank of the talonid. It is present
on all lower carnassial teeth, with striations running steeply
inclined from apical to buccal. The antagonistic structure to
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In Sarcophilus and Thylacinus, the rather large meta-
cone occludes with the distal talonid ank, 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 para-
cone occludes with the mesial talonid ank, 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 Dasyurus is also present in the ultimate locus (M4) of
the more strongly carnassialized molars of Sarcophilus and
Thylacinus.
OFA analysis of carnivoran taxa
Viverra tangalunga (weakly carnassialized dentition)
The viverrid Viverra tangalunga has a weakly carnassial-
ized carnivoran dentition. For the OFA analysis, specimen
SMF 697 was chosen. The m1 talonid and the P4 protocone
With progressing wear, the facet PA-m on M4 extends
lingually and wraps around the paracone. This is the result
of the hypoexid moving along the paracone during occlu-
sion. On the m4 of Sarcophilus and Thylacinus, this leads to
the formation of a distinctive polished groove on the buccal
talonid ank, with striations formed by attrition in the hypo-
exid (Fig. 4a, b).
Metacone-talonid-occlusion
Facet hd-db forms on the distal ank of the talonid on the
lower carnassials of Dasyurus, with the exception of m4. It
starts forming along the posthypocristid and with progres-
sive wear it extends onto the entire distal talonid ank. The
striations on the facet run at a steep inclination from apical
to buccal. The posthypocristid occludes with the praemetac-
rista of the upper molars. Facet ME-ml forms on the mesial
ank 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.
Fig. 4 Tooth wear on m4 (a) and M4 (b) of Sarcophilus harrisii (NMB 10548) and on m4 (c) and M4 (d) of Thylacinus cynocephalus (NMB 2526).
Dashed lines mark the visible edges of facets. Solid lines indicate the inclination of striations. Photographs of epoxy casts
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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 ank of m1 is also initiated
in timestep 6. This area of contact shifts in cervical direction
along the distal protoconid ank with further upwards move-
ment of the lower molar and extends into the hypoexid
as well as the post-carnassial molars (M1, M2 and m2)
are well developed. The complete power stroke comprises
142 timesteps (Fig. 5a). The initial occlusal contact occurs
between the apex of the P4 paracone and the apex of the m1
paraconid, which initiates the rst cutting contact between
the upper and lower carnassial blades. In timestep 6, a sec-
ond cutting contact occurs on the lingual side between the
Fig. 5 Results of the OFA-analysis of the power strokes of Viverra
tangalunga (a) and Speothos venaticus (b), showing the total occlusal
area from the initial occlusal contact up to the point of centric occlu-
sion. Duration of the carnassial blade occlusion (cbo) and hypoexid
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 render-
ings from µCT data
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Mammal Research
praeparacrista and the distal m1 trigonid ank. 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 ank. Even-
tually, this contact area shifts into the hypoexid groove
around timestep 86. An additional contact area at the distal
trigonid ank is detected at timestep 34 with the M1 para-
cingulum, which occludes with the apex of the protoconid.
This contact area also shifts in cervical direction with further
tooth movement along the distal trigonid ank 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 fur-
ther tooth movement on the mesial hypoconid ank and the
distal paracone ank, and eventually shifts into the hypo-
exid. Occlusion between hypoexid 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 denti-
tion 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 move-
ment was stopped by occlusion of the tip of the m2 main
cusp (protoconid) with the distal protocone ank 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 hypoexid 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. 6a). 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 direc-
tion with further upwards movement of the lower molar.
Starting with timestep 18, there are two points of active cut-
ting 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
around timestep 107, whereas it shifts in lingual direction
along the praeparacrista towards the paracone apex on M1.
In timestep 30, the buccal ank 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 ank 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 ank that occludes with the paras-
tyle and paracone. The occlusal contacts between M1 and
the distal protoconid ank remain active until the point of
centric occlusion.
Between timesteps 99 and 125, occlusal contact between
the mesial paracone ank along the praeparacrista and the
distal hypoconid ank along the posthypocristid occurs.
In timestep 82, a rst contact occurs between the mesial
protocone ank of M1 and the apex of the m1 metaconid.
With further tooth movement, this area of contact expands
to cover the entire distal metaconid ank and most of the
distal protocone ank up to the point of centric occlu-
sion. Initial occlusal contact in the m1 talonid basin occurs
in timestep 121 between the entoconid and the distal M1
protocone ank. This area of contact expands to cover the
entire entoconid ank with further tooth movement, and a
second occlusal contact between the mesial protocone ank
and the hypoconulid is initiated in timestep 126. These con-
tacts 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. 5b). Initial occlusal con-
tact 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 rst postcarnassial occlusion is detected between the M1
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Mammal Research
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 metacris-
tid of m4 and the paracrista of M4 is calculated between
the apex of the protoconid and the parastyle. This area of
parastyle, is calculated. With a further upwards movement
of the lower molar, cutting beween the metacristid and the
praeparacrista eventually includes the whole mesial para-
cone ank. 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
Fig. 6 Results of the OFA-analysis of the power strokes of Dasyurus
viverrinus (a) and Thylacinus cynocephalus (b), 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 hypo-
exid 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
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Mammal Research
the occlusion of the buccal entoconid ank and the post-
protocrista. 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 ank 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, speci-
men ZMB_Mam_036877 was chosen. The complete chew-
ing path is comprised of 168 steps and consists of one
single phase until the point of centric occlusion is reached
(Fig. 6b). Initial occlusal contact occurs between the meta-
crista 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 rst 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 anks and approach
each other with further tooth movement, eventually wrap-
ping around the carnassial notch of the lower molar and fus-
ing in timestep 58. In timestep 31, occlusal contact occurs
between the mesial paracone ank of M3 and the distal tri-
gonid ank of m3. With further tooth movement, this con-
tact area expands along the praeparacrista and postparacrista
of M3 and along the distal trigonid ank of m3 in cervical
direction. This occlusal contact remains up until timestep
120. In timestep 61, two points of contact between the car-
nassial blades of M2 and m3 are detected. The rst occurs
on the buccal side, in proximity to the metastyle and the pro-
toconid. 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 ank
of M2 and the distal trigonid blade of m2 occurs in timestep
62. With further tooth movement, the area of occlusal con-
tact expands along the postparacrista and the praepacacrista
of M2 and expands in cervical direction of both antagonistic
anks and remains up until timestep 127. In timestep 86,
the rst occlusal contact between the carnassial blades of
M1 and m2 is detected. It occurs on the buccal side of the
occlusal contact successively expands lingually and even-
tually involves the paracone occluding with the distal car-
nassial notch. At timestep 96, a second occlusal contact is
calculated between the metacristid of m4 and the praepro-
tocrista of M4, starting with the occlusion of the apices of
protocone and metaconid. An additional point of contact
between praeprotocrista and metacristid, occurring buc-
cally from the metacristid carnassial notch, is calculated at
timestep 109. These two points of cutting between praepro-
tocrista 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 mov-
ing 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 cut-
ting function while the lower jaw is moving upwards. Initial
contact between the metacristid of m2 and the praeparac-
rista of M2 is calculated at timestep 86. This area of contact
expands with further tooth movement towards lingual along
the distal paracone ank. A second point of occlusal con-
tact 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 ank expands
lingually onto the mesial protocone ank, 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 cal-
culated at the mesial and distal trigonid anks, occlusion
also occurs on the talonid. At timestep 91, the rst 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 posthy-
pocristid 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
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Mammal Research
between the mesial paracone ank of M4 and the distal
trigonid ank of m4 occurs in timestep 53. This contact
remains during most of the rest of the chewing path, with
the distal trigonid ank of m4 occluding along the paracone
of M4 up until 15 timesteps before centric occlusion. Even-
tually, the contact wraps around the paracone and covers
the hypoexid. In addition to the trigonids occluding with
the paracones and metacones, there are occlusal contacts
between the talonids and the paracones and metacones. The
rst contact occurs in timestep 63 between the distal talonid
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 follow-
ing timesteps and merge in timestep 118, wrapping around
the carnassial notch of the lower molar. The rst contact
Fig. 7 Evolutive connection of
carnassialization and the “tren-
chant” talonid heel as exemplied
in carnivoran and dasyuromorph
taxa. Carnassial occlusal contact
(red) and paracone/hypoexid
occlusal contact (blue) both
increase up to the point where the
talonid is completely reduced (as
in Felis silvestris). Upper molars
in occlusal view, lower molars in
buccal view. Mesial is to the right
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Mammal Research
and thus the opening of the hypoexid groove, which con-
nects to the distal trigonid ank. As a result, the shearing
function of the trenchant talonid is enhanced. In carnassial
teeth with tricuspid talonids, as in Dasyurus, Ichneumia,
Viverra spp., and the presence of multiple facets within the
talonid basin points to a stronger emphasis on a crushing
function, while the paracone/hypoexid function is only
weakly pronounced. The OFA reconstructions also revealed
a functional dierence, with a shorter paracone/hypoexid
occlusal contact before centric occlusion in Dasyurus (27%
of timesteps) and Viverra (12%) than in Speothos (46%) and
Thylacinus (35%). In all taxa, steeply lingually inclined stri-
ations on the facets indicate a mostly orthal tooth movement
during the power stroke, to which the paracone/hypoexid
occlusion contributes in the strongly carnassialized condi-
tion with a trenchant heel.
Solé and 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 molari-
forms 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 and Ladevèze 2017). The reuse of the
hypoexid groove for shear-cutting in carnassials appar-
ently 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 Megazostro-
don which dier from those seen in carnassials, with the
mesial ank 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 ank of
cusp c (metaconid), and not with cusp d (Jäger et al. 2019).
Occlusion of cusp A and cusp d is established later in mam-
malian evolution, after triangulation of the trigon and trigo-
nid cusps. At this point the occlusal relationships become
comparable to those of carnassial teeth with a unicuspid tal-
onid, where cusp A (paracone) is occluding between the uni-
cuspid talonid cusp and cusp a (protoconid). Thus, a groove
exhibiting functional resemblance to the hypoexid of the
tribosphenic molar (and its derivatives) is present in morga-
nucodontan teeth. Whether the presence of the hypoexid
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 rst tal-
onid cusp to evolve (hypoconid or hypoconulid) is debated
ank of m3 and the mesial metacone ank 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 occlu-
sal contact expands in buccal direction along the praemeta-
crista and along the posthypocristid towards the hypocone.
This occlusion remains until timestep 112. In timestep 100,
the rst occlusal contact between the distal paracone ank
of M3 and the mesial talonid ank of m3 is detected. This
contact area remains small and is only active for a shorter
duration, up until timestep 136. The rst occlusal contact
between the distal talonid ank of m2 and the mesial meta-
cone ank 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 meta-
cone and from the hypoconulid towards the hypoconid. It
remains active until timestep 131.The mesial talonid ank
of m2 occludes with the distal paracone ank of M2 rst
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 uni-
cuspid 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. Occlu-
sion occurs between the carnassial blades and between the
distal paracone and mesial talonid ank. The crown struc-
ture of the lower carnassials remains more conservative in
carnivorans and dasyuromorphs, while more apomorphic
adaptations are present in the upper dentition. Dierences
in the crown morphology of the upper teeth in return result
in some occlusal dierences between carnivorans and dasy-
uromorphs. In marsupials, which have multiple carnassial
teeth, additional occlusion occurs between the mesial meta-
cone ank and the distal talonid ank (except for the last
lower carnassial, which lacks a distal upper antagonist).
Occlusal contact between the buccal protocone ank and
the lingual hypoconid ank is generally reduced in carnas-
sials with unicuspid talonids, indicating loss of the crush-
ing function. For Thylacinus 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 hypoco-
nulid) and loss of the basined talonid in carnassials allows
an enlargement of the mesial talonid (hypoconid) ank
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Mammal Research
hypoexid exhibit a remarkable structural resemblance to
molariforms of non-tribosphenic mammaliaforms and mam-
mals, 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
and 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. Repe-
nomamus 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, func-
tionally getting back to the pretribosphenic condition.
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 (Museum für Naturkunde, Ber-
lin), Jörn Köhler (HLMD), Katrin Krohmann (SMF), Frieder Mayer
(Museum für Naturkunde, Berlin) and Irina Ruf (SMF, Senckenberg
Gesellschaft für Naturforschung). We thank P. David Polly (Indiana
University Bloomington) and one anonymous reviewer for reviewing
this manuscript and providing constructive comments and suggestions.
This research was funded by a doctoral grant to A. J. Lang by the Stu-
dienstiftung des deutschen Volkes. Open access funding enabled and
organized by project DEAL.
Funding This study was funded by a doctoral grant to A. J. Lang by
the Studienstiftung des deutschen Volkes.
Open Access funding enabled and organized by Projekt DEAL.
Data availability Supplementary materials including the OFA project
les used in this study are available in the gshare repository, https://
doi.org/10.6084/m9.gshare.26067505. Scan data of the specimens
used in the OFA analyses is available from the corresponding author
on reasonable request.
Declarations
Conict of interest The authors declare no conict of interest.
Open Access This article is licensed under a Creative Commons
Attribution 4.0 International License, which permits use, sharing,
adaptation, distribution and reproduction in any medium or format,
as long as you give appropriate credit to the original author(s) and the
source, provide a link to the Creative Commons licence, and indicate
if changes were made. The images or other third party material in this
article are included in the article’s Creative Commons licence, unless
indicated otherwise in a credit line to the material. If material is not
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use is not permitted by statutory regulation or exceeds the permitted
use, you will need to obtain permission directly from the copyright
holder. To view a copy of this licence, visit http://creativecommons.
org/licenses/by/4.0/.
(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 tal-
onid. In these teeth, a groove forms between cusps a and c,
which structurally resembles the hypoexid groove of car-
nassials 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 hypoexid groove in carnassial teeth provides
an additional shearing locus between the paracone and the
unicuspid talonid, which is further enhanced by the more
simplied talonid morphology of highly carnassialized teeth
(Fig. 7). 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 tri-
gonid ank. This notch increases the cutting eciency, as
it duplicates the function of the main carnassial notch at a
smaller scale.
The striations on the facets associated with the paracone/
hypoexid occlusion of the carnassials show a uniform ori-
entation. They indicate that the slightly obliquely inclined
tooth movement, as initiated with carnassial blade occlu-
sion, is maintained during the power stroke. This function
is comparable to some extent to the hypoexid function in
cladotherian dryolestidans, although the guiding component
is more pronounced in these pretribosphenic teeth than in
the carnassials (Schultz and Martin 2011, 2014). A change
of the inclination of the striations on the distal trigonid ank
near the hypoexid, as observed in dryolestidan molars
(Schultz and Martin 2011), was not observed in the hypo-
exids of carnassial teeth. Thus, a crushing component,
which would result in a change of striation inclination, can-
not be inferred for the carnassial trenchant heel. The guid-
ing function of paracone/hypoexid occlusion in carnassials
can be attributed to the eect 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 neuro-
logical requirements for tooth alignment to the initial occlu-
sal contact of the power stroke (Evans and Sanson 2006).
The development of a trenchant unicuspid talonid with
a shearing hypoexid evolved multiple times from the tri-
bosphenic pattern in therians with carnassial adaptations,
resulting in similar occlusal patterns, indicating an increase
in faunivory. The therian carnassials with pronounced
1 3

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