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Phylogenetic relationships of higher taxonomic groups with the Dicynodontia. The topologies from the Permian and the Triassic taxa are taken from and simplified after Fröbisch (2006) and Maisch (2001), respectively. The evolution of the main characters associated with an upright posture of the hind limb is plotted on the cladogram, emphasizing a gradual evolution of the change in hind limb motion. The phylogenetic position of Tetragonias njalilus is within the basalmost clade of the kannemeyeriiform dicynodonts, the Shansiodontidae. Tetragonias possesses all characters associated with an upright hind limb posture and thus represents an ideal model for the locomotion of derived dicynodonts.
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A general locomotor model for derived dicynodont anomodonts is proposed on the basis of a functional analysis of the pelvic girdle and entire hind limb of the medium-sized Middle Triassic dicynodont Tetragonias njalilus. The joint mobility of the hind limb is examined, and a hind limb step cycle is reconstructed. The data provided in this case stud...
Citations
... More erect limbs may have existed as early as the Permian. Indeed, several lineages of Permo-Triassic therapsids, such as Anomodontia and Cynodontia, have been described as having had a "semi-erect" posture based on anatomical and biomechanical evidence (Blob, 2001;Fahn-Lai et al., 2018;Fröbisch, 2006). Today, posture in mammals and in older stem taxa, such as Dimetrodon, still raises many questions, triggering numerous studies that enrich our knowledge of the evolution of locomotion in synapsids (Brocklehurst et al., 2022;Jones et al., 2021;Regnault et al., 2020). ...
Extant amniotes show remarkable postural diversity. Broadly speaking, limbs with erect (strongly adducted, more vertically oriented) posture are found in mammals that are particularly heavy (graviportal) or show good running skills (cursorial), while crouched (highly flexed) limbs are found in taxa with more generalized locomotion. In Reptilia, crocodylians have a “semi-erect” (somewhat adducted) posture, birds have more crouched limbs and lepidosaurs have sprawling (well-abducted) limbs. Both synapsids and reptiles underwent a postural transition from sprawling to more erect limbs during the Mesozoic Era. In Reptilia, this postural change is prominent among archosauriforms in the Triassic Period. However, limb posture in many key Triassic taxa remains poorly known. In Synapsida, the chronology of this transition is less clear, and competing hypotheses exist. On land, the limb bones are subject to various stresses related to body support that partly shape their external and internal morphology. Indeed, bone trabeculae (lattice-like bony struts that form the spongy bone tissue) tend to orient themselves along lines of force. Here, we study the link between femoral posture and the femoral trabecular architecture using phylogenetic generalized least squares. We show that microanatomical parameters measured on bone cubes extracted from the femoral head of a sample of amniote femora depend strongly on body mass, but not on femoral posture or lifestyle. We reconstruct ancestral states of femoral posture and various microanatomical parameters to study the “sprawling-to-erect” transition in reptiles and synapsids, and obtain conflicting results. We tentatively infer femoral posture in several hypothetical ancestors using phylogenetic flexible discriminant analysis from maximum likelihood estimates of the microanatomical parameters. In general, the trabecular network of the femoral head is not a good indicator of femoral posture. However, ancestral state reconstruction methods hold great promise for advancing our understanding of the evolution of posture in amniotes.
Abstract
We use 3D microanatomical parameters measured at the femoral head to study femoral posture in amniotes. We show that these parameters are not good indicators of femoral posture. Methods of ancestral state reconstruction hold great promise for improving our understanding of the evolution of posture in amniotes.
... Therapsid locomotion and its evolution has been subject of various studies (e.g., Kemp 1978;King 1985;Walter 1986;Ray 2006Kemp 1980Ray 2006see summary in Fröbisch 2006). Those studies often focussed on very specific taxa (e.g., Fröbisch 2006) or rather on isolated parts of the body, e.g., the vertebral column (Jones et al. 2021) or the hindlimbs (Fröbisch 2006). Very general reoccurring patterns of biomechanical adaptations found across Tetrapoda are rarely regarded. ...
... Therapsid locomotion and its evolution has been subject of various studies (e.g., Kemp 1978;King 1985;Walter 1986;Ray 2006Kemp 1980Ray 2006see summary in Fröbisch 2006). Those studies often focussed on very specific taxa (e.g., Fröbisch 2006) or rather on isolated parts of the body, e.g., the vertebral column (Jones et al. 2021) or the hindlimbs (Fröbisch 2006). Very general reoccurring patterns of biomechanical adaptations found across Tetrapoda are rarely regarded. ...
... In birds these are the synsacrum and ischium and in mammals this is the complex formed by ischium and pubis (Romer and Frick 1966;Nickel et al. 1968). In several of the more advanced (Triassic) therapsids, the ilium as well as the ischium have posterior processes, which may well have served as origins of the femur retracting muscles (Fröbisch 2006). The exact differentiation of the muscles is of minor importance in this context, because, from a biomechanical point of view, it is important that they muscularly connect the pelvis and the femur. ...
Therapsids covered the entire spectrum of terrestrial locomotion from sprawling to parasagittal. Switching between sprawling and more erect locomotion may have been possible in earlier taxa. First, the axial skeleton shows little regionalization and allows lateral undulation evolving then increasingly towards regionalization enabling dorsoventral swinging. During terrestrial locomotion, every step invokes a ground reaction force and functional loadings which the musculoskeletal system needs to accomodate. First insights into the functional loading regime of the fore- and hind limb skeleton and the body stem of therapsids presented herein are based on the assessment and preliminary measurements of the historical collection of therapsids exhibited in the Paleontological Collection of Eberhard Karls-Universität Tübingen, Germany. The specimens included are the archosaur Hyperodapedeon sanjuanensis, the early synapsid Dimetrodon limbatus, and the therapsids Keratocephalus moloch, Sauroctonus parringtoni, Tetragonias njalilus, and Belesodon magnificus. The vertebral columns and ribs of the mounts were carefully assessed for original fossil material and, when preserved, ribs, sacral, and anterior caudal vertebrae were measured. The body of a tetrapod is exposed to forces as well as bending and torsional moments. To resist these functional stresses, certain musculoskeletal specializations evolved. These include: 1) compression resistant plate-like pectoral and pelvic girdle bones, 2) a vertebral column combined with tendinous and muscular structures to withstand compressive and tensile forces and moments, and 3) ribs and intercostal muscles to resist the transverse forces and torsional moments. The legs are compressive stress-resistant, carry the body weight, and support the body against gravity. Tail reduction leads to restructuring of the musculoskeletal system of the pelvic girdle.
... The postcranial anatomy of dicynodonts points to a postural dichotomy, consisting of abducted forelimbs and nearly adducted hind limbs (Watson, 1960;Cox, 1972;Cluver, 1978;King, 1981a;Ray and Chinsamy, 2003;Ray, 2006;Morato et al., 2008). Fröbisch (2006) suggested parasagittal limb postures for medium-sized Middle Triassic dicynodonts, adopting a highly adducted hind limb posture during stance and most of its stride. However, the reconstruction of abducted and adducted posture remains conflicting, because it is based only on mutually incompatible interpretations of ambiguous osteology (Lai et al., 2018). ...
... Generally, the forelimb step cycle in dicynodonts was changed from a primitive abducted posture to an adducted posture in more derived taxa (e.g. King, 1981a,b;Walter, 1986;Fröbisch, 2006). The trackway pattern of P. argentinae nov. ...
Quadruped trackways of large pentadactyl footprints are reported from the Middle Triassic (Anisian-Ladinian) Cerro de las Cabras Formation of the Cuyo Basin, Mendoza Province, central-western Argentina. The track-bearing strata are interpreted as deposited by sheetfloods in a mixed flat where water was ponded in a playa-lake setting. The vertebrate trackways are assigned to the ichnogenus Pentasauropus, originally described from the Upper Triassic Elliot Formation of South Africa, based on the presence of five equally spaced digit imprints that form an anteriorly convex broad arcuate pattern. A new ichnospecies, Pentasauropus argentinae nov. isp., is erected for the Argentinian material because of the distinct heteropody, inward rotation of the pes and outward rotation of the manus imprints, and the presence of palm/sole traces, and the diagnosis of the ichnogenus is emended. Pes/manus set arrangement and trackway patterns indicate a sprawling limbed trackmaker with an abducted posture for the fore-limbs and at least a semi-abducted posture for the hindlimbs, which suggests that the trackmaker was a kannemeyeriiform dicynodont. Associated archosaur ichnotaxa (Chirotherium barthii, Chirotherium cf. C. rex, Isochirotherium cf. I. coureli) point to a Middle Triassic age for the trackway-bearing strata in agreement with bracketing geochronological data. The rare occurrence of the therapsid footprint Dicynodontipus isp. is also compatible with the inferred age. The moderate abundance and oldest occurrence of Pentasauropus from three areas in Argentina suggest an origin for this ichnogenus in southwestern Gondwana, and presumably this area was a faunal exchange gate between southeastern and southwestern Gondwana and south Gondwana and North America
... Nevertheless, several species of dicynodonts (such as Eodicynodon, Lystrosaurus, Tetragonias, Dinodontosaurus and Jachaleria) have a rounded calcaneum and lack evidence of an ossified tuber calcis (Watson, 1913;King, 1991;Rubidge, King & Hancox, 1994;Vega-Dias & Schultz, 2004;Fröbisch, 2006;Morato et al., 2008). In such cases, the insertion of the musculus gastrocnemius and the other calf muscles is inferred to have been at the plantar face of the calcaneum, following the sauropsid condition (Haughton, 1864(Haughton, -1866Fröbisch, 2003;Morato, 2006). The only known exception to this morphology is the calcaneum of Dicynodontoides (=Kingoria). ...
... In this case, the posterior process of the Dicynodontoides calcaneum was considered homologous to the mammalian tuber calcis (King, 1985). However, in spite of the data provided by King (1985), we follow Fröbisch (2003) and Morato (2006), considering that the insertion site of the musculus gastrocnemius was in the plantar face of the foot. In this way, even though the presence of an ossified tuber calcis is not an anatomical feature that occurs within the clade Dicynodontia, the postero-plantar region of their feet is considered the main area for the insertion of the musculus gastrocnemius via the calcaneum tendon (Fröbisch, 2003(Fröbisch, , 2006Morato, 2006). ...
... However, in spite of the data provided by King (1985), we follow Fröbisch (2003) and Morato (2006), considering that the insertion site of the musculus gastrocnemius was in the plantar face of the foot. In this way, even though the presence of an ossified tuber calcis is not an anatomical feature that occurs within the clade Dicynodontia, the postero-plantar region of their feet is considered the main area for the insertion of the musculus gastrocnemius via the calcaneum tendon (Fröbisch, 2003(Fröbisch, , 2006Morato, 2006). The triangular shape of the SLIA-1 pedal tracks could be derived from the presence of soft tissues in the posterior margin of the pes, because it is to be expected that the calcaneum tendon was inserted in the postero-plantar face of the feet. ...
Tetrapod tracks in eolianites are widespread in the fossil record since the late Paleozoic. Among these ichnofaunas, the ichnogenus Chelichnus is the most representative of the Permian tetrapod ichnological record of eolian deposits of Europe, North America and South America, where the Chelichnus Ichnofacies often occurs. In this contribution, we describe five sets of tracks (one of which is preserved in cross-section), representing the first occurrence of Dicynodontipus and Chelichnus in the “Pirambóia Formation” of southern Brazil. This unit represents a humid desert in southwestern Pangea and its lower and upper contacts lead us to consider its age as Lopingian–Induan. The five sets of tracks studied were compared with several ichnotaxa and body fossils with appendicular elements preserved, allowing us to attribute these tracks to dicynodonts and other indeterminate therapsids. Even though the “Pirambóia Formation” track record is sparse and sub-optimally preserved, it is an important key to better understand the occupation of arid environments by tetrapods across the Permo–Triassic boundary.
... The NMT were among the first terrestrial tetrapods to have a wide variety of body sizes and to adapt to various types of locomotion, from a sprawling to parasagittal posture [Kemp, 2005;Fröbisch, 2006], and exploit a variety of ecological niches, from arboreal to subterranean [Smith, 1987;Fröbisch and Reisz, 2009;Nasterlack et al., 2012]. Their fossils are found today on every continent, including Antarctica [Kitching et al., 1972;Colbert and Kitching, 1981]. ...
The origin and evolution of the mammalian brain has long been the focus of scientific enquiry. Conversely, little research has focused on the palaeoneurology of the stem group of Mammaliaformes, the Permian and Triassic nonmammaliaform Therapsida (NMT). This is because the majority of the NMT have a non-ossified braincase, making the study of their endocranial cast (sometimes called the “fossil brain”) problematic. Thus, descriptions of the morphology and size of NMT endocranial casts have been based largely on approximations rather than reliable determination. Accordingly, here we use micro-CT scans of the skulls of 1 Dinocephalia and 3 Biarmosuchia, which are NMT with a fully ossified braincase and thus a complete endocast. For the first time, our work enables the accurate determination of endocranial shape and size in NMT. This study suggests that NMT brain size falls in the upper range of the reptilian and amphibian variation. Brain size in the dicynodont Kawingasaurus is equivalent to that of early Mammaliaformes, whereas the Dinocephalia show evidence of a secondary reduction of brain size. In addition, unlike other NMT in which the endocast has a tubular shape and its parts are arranged in a linear manner, the biarmosuchian endocast is strongly flexed at the level of the midbrain, creating a near right angle between the fore-and hindbrain. These data highlight an unexpected diversity of endocranial size and morphology in NMT, features that are usually considered conservative in this group.
... can also be excluded (Romer 1956;Fröbisch 2006). Among the various possibilities with respect to the manual and pedal oste- ological record, the Contiichnus tazelwurmi trackmaker seems to be characterised by a greater affinity with Late Permian and Early to Middle Triassic bauriiids therapsids, which have rela- tively small and light-built representatives, unfortunately mostly known from their cranial osteology than from the manual and pedal ones (e.g. ...
In this paper, a revision of tracks referred to as Chelichnus tazelwürmi is reported. The performed analysis,
consisting of a holistic approach by means of a mainly morphological analysis, and a secondarily functional
one, led to the proposal of a new ichnogenus, named as Contiichnus tazelwurmi. The three dimensional
morphology of the tracks allows for the inference of a complex cycle of locomotion by the trackmakers. The
tracks were formed in the main phases (i.e. touch-down, weight-bearing and kick-off) by different axes of
body load and transference, indicating that the whole fore autopod was involved in the cycle of locomotion
and actively contacted the substrate, while for the hind autopod the functional prevalence was markedly
centro-medial. Some track features suggest a therapsid-grade synapsid as potential trackmaker. However,
the reconstructed autopodial structure does not correlate with known autopods from the Late Permian
body fossil record. These observations stress the importance of tetrapod ichnology studies in improving
knowledge in the field of vertebrate palaeontology.
... On the one hand, these higher scores may reflect a more diverse range of locomotory possibilities permitted by the use of both a 'reptile-like gait' and 'mammal-like gait' in biarmosuchians, gorgonopsians and anomodonts, whereas cynodonts and Moschops were more constrained to a single type of posture, perhaps more parasagittal. But on the other hand, this is inconsistent with the fossil record of footprints attributed to dinocephalians, which supports a partial sprawling posture (Gand et al. 2000;Surkov et al. 2007) and the hypothesis that some dicynodonts evolved a more upright posture independently because of the biomechanical constraints imposed by their large body size (Blob 2001;Fröbisch 2006). Finally, the range of semi-circular canal radii of sprawling tetrapods overlaps that of mammals and NMT (Fig. 6). ...
Biarmosuchia, as the basalmost group of Therapsida (the stem group of mammals), are important for understanding mammalian origins and evolution. Unlike other therapsid groups, the bony labyrinth of biarmosuchians has not yet been studied, despite insightful clues that bony labyrinth morphology can provide to address palaeobiology and phylogeny of extinct animals. Here, using CT scanning, surface reconstruction and a 3D geometric-morphometric protocol of 60 semi-landmarks on the bony labyrinth of 30 therapsids (including three Mammaliaformes), it is demonstrated that bony labyrinth morphology of biarmosuchians is very
distinctive compared to that of other therapsids. Despite the primitive nature of their cranial morphology, biarmosuchians display highly derived traits in the structure of the bony labyrinth. The most noticeable are the presence of a long and slender canal linking the vestibule to the fenestra vestibuli, an enlarged and dorsally expanded anterior canal, and the absence of a secondary common crus (except for one specimen), which sets them apart from other non-mammalian therapsids. These characters provide additional support for the monophyly of Biarmosuchia, the most recently recognized major therapsid subclade. Although implications of the derived morphology of the biarmosuchian bony labyrinth are discussed, definitive interpretations are dependent on the discovery of well-preserved postcranial material. It nevertheless sheds light on a previously overlooked diversity of bony labyrinth morphology in non-mammalian therapsids.
... The fossil record of Synapsida is exceptional in that it documents in much detail the transition from basal, pelycosaur-grade synapsids to derived synapsids and the acquisition of increasingly large numbers of mammalian features, such as the mammalian phalangeal formula, upright locomotion, bony secondary palate, the mammalian middle ear, and ecological specializations (e.g., Olson 1944Olson , 1959Allin 1975;Cluver 1978;Hopson 1995;Fröbisch 2006;Luo 2007;Fröbisch and Reisz 2009). ...
This study investigates diversity patterns of Synapsida in the Permian-Triassic sequence of the Karoo Basin, South Africa. Permian-Triassic synapsids represent the dominant terrestrial tetrapods of their time and play a central role in assessing the impact of the end-Permian mass extinction on terrestrial ecosystems. On the regional scale of the Karoo Basin, synapsid diversity shows a mid-Permian extinction and a pronounced extinction event at the end of the Permian, whereas the subclades of Synapsida exhibit clade-specific diversity patterns. Taxonomic diversity estimates (TDEs) of Synapsida and its subclades are not significantly correlated with outcrop area for the complete time series. However, after exclusion of the Lystrosaurus Assemblage Zone from all data series, the TDEs of the majority of synapsid subclades show statistically significant strong positive correlations with outcrop area. Nonetheless, diversity residuals, resulting from modeled diversity estimates, exhibit clade-specific patterns with varying support for a mid-Permian event and strong support for an end-Permian extinction. The results confirm studies at the global scale and imply that synapsid diversity in the Karoo Basin is at least partially biased by the Permian-Triassic terrestrial rock record. Moreover, Anomodontia, the most speciose clade of non-mammalian synapsids, is not the sole driver of the synapsid diversity signal. Instead, there seems to be a general synapsid pattern, with each subclade diverging from this pattern to varying degrees for clade-specific reasons. Thus, despite the obvious rock record bias, the end-Permian extinction maintains its major impact on synapsid diversity and therefore on the composition and structure of past and present terrestrial ecosystems.
... Anomodonts are the most speciose and morphologically diverse clade of Permian-Triassic terrestrial tetrapods, representing the dominant herbivores of their time and dominating terrestrial vertebrate ecosystems in numbers of individuals and occupation of ecological guilds (Fröbisch, 2009;Hotton, 1986;Pearson et al., 2013). They ranged in body size from very small (10-15 cm body length) to large (2-3 m body length), and included fully terrestrial, semi-aquatic, fossorial and arboreal ecomorphs with a wide range of feeding adaptions (Cluver, 1978;Cox, 1972;Fröbisch, 2006;Reisz, 2009, 2011;Germain and Laurin, 2005;Kriloff et al., 2008;Ray et al., 2005;Surkov and Benton, 2008). Anomodonts had a global distribution with fossils known from every continent, but only very few taxa, e.g. ...
The quality of the fossil record of anomodont synapsids, one of the major clades of Permian–Triassic terrestrial tetrapods, is assessed. A Character Completeness Metric (CCM2) is calculated for each taxon and consecutive time intervals at a global scale and in the South African Karoo Basin. The mean completeness score is 66.80% (globally) and 77.37% (regionally) with completeness ranging between 60.12% and 91.33% per time interval. Up-to-date taxic, phylogenetic and residual diversity estimates confirm the general biodiversity trends recovered by recent analyses. The consistently high CCM2 scores throughout their evolutionary history together with a lack of correlation with biodiversity patterns and sampling proxies document a high quality of the known anomodont fossil record. In fact, when compared to other vertebrate groups, the completeness values for anomodonts are exceptionally high. Yet, whether this pattern results from the unrivalled record of the Karoo Basin or whether it is clade-specific and unique to anomodonts remains to be tested.
... Only the Kannemeyeriiformes underwent a significant diversification during the Triassic, with roughly 40 known species [4,8]. Unlike Permian anomodonts, however, which are known from ,90 species spanning mouse-to-rhinoceros sizes and occupying an array of niches (including fossorial and arboreal forms) [9,10], all kannemeyeriiforms were medium-to large-bodied [11], graviportal herbivores with relatively erect posture and gait [12,13]. ...
The large dicynodont Eubrachiosaurus browni from the Upper Triassic Popo Agie Formation of Wyoming is redescribed. Eubrachiosaurus is a valid taxon that differs from Placerias hesternus, with which it was previously synonymized, by greater anteroposterior expansion of the scapula dorsally and a very large, nearly rectangular humeral ectepicondyle with a broad supinator process. Inclusion of Eubrachiosaurus in a revised phylogenetic analysis of anomodont therapsids indicates that it is a stahleckeriid closely related to the South American genera Ischigualastia and Jachaleria. The recognition of Eubrachiosaurus as a distinct lineage of North American dicynodonts, combined with other recent discoveries in the eastern USA and Europe, alters our perception of Late Triassic dicynodont diversity in the northern hemisphere. Rather than being isolated relicts in previously therapsid-dominated regions, Late Triassic stahleckeriid dicynodonts were continuing to disperse and diversify, even in areas like western North America that were otherwise uninhabited by coeval therapsids (i.e., cynodonts).
