Browsing by Author "Benoit, Julien"

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    A new middle Permian burnetiamorph (Therapsida: Biarmosuchia) from the South African Karoo filling a gap in the biarmosuchian record
    (The Evolutionary Studies Institute, 2024-09) Matlhaga, Fonda; Benoit, Julien; Rubidge, Bruce S
    Biarmosuchia, the most basal therapsid clade, is represented by relatively few specimens known from Permian deposits in Russia and southern Africa. In both the Guadalupian (middle Permian) and Lopingian (late Permian), biarmosuchians represent less than 1% of the fossil record at the specimen level. Here, we describe a new burnetiamorph biarmosuchian, Impumlophantsi boonstrai, based on a partial skull and associated postcrania from the upper Tapinocephalus Assemblage Zone. It is characterized by the presence of a low nasal crest with a unique morphology among burnetiamorphs. Inclusion of this taxon in an updated phylogenetic analysis of biarmosuchians indicates that this specimen is one of the most basal burnetiamorphs, representing the only record of this grade from the middle Permian.
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    The bony labyrinth of late Permian Biarmosuchia: palaeobiology and diversity in non-mammalian Therapsida
    (2017-07) Benoit, Julien; Manger, Paul R; Fernandez, Vincent; Rubidge, Bruce S
    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.
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    Cranial morphology and phylogenetic relationship of the enigmatic dinocephalian Styracocephalus platyrhynchus from the Karoo Supergroup, South Africa
    (Evolutionary Studies Institute, 2019-09) Fraser-King, Simon W.; Benoit, Julien; Day, Michael O.; Rubidge, Bruces S.
    Styracocephalus platyrhynchus is an unusual dinocephalian therapsid, known only from a handful of specimens from the Tapinocephalus Assemblage Zone of South Africa. It has had a chequered taxonomic history, largely because it is characterized by cranial pachyostosis and the presence of horn-like structures that project posteriorly from the temporal region; these features are found in the clades Burnetiamorpha and Dinocephalia. Its affinities have been further obfuscated by a lack of well-preserved material. This paper presents a description of a well-preserved skull referable to Styracocephalus from the western Karoo Basin and provides a revised generic diagnosis for the genus. This study – incorporating comparative anatomy,CT scanning, and cladistic analysis – reveals new character information that was not evident from pre-existing Styracocephalus material, and incorporates this into a new phylogenetic analysis. Our analysis recovers Styracocephalidae as a well-supported, monotypic family within Tapinocephalia, which is characterized by: prominent pachyostotic nasal and supraorbital bosses; two posteriorly projecting crest-like protuberances comprising contributions by the postorbital, squamosal and tabular bones; weak lingual heels on the incisor and postcanine dentition present with a moderate upper and lower canine. As Styracocephalus is restricted to the upper part of the Tapinocephalus Assemblage Zone, it may be a useful biostratigraphic index taxon in future.
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    Cranial orientation and the lateral semicircular canal in primates: implications for palaeobiological reconstructions and the evolution of locomotor repertoires
    (University of the Witwatersrand, Johannesburg, 2023) Pestana, Christopher; Benoit, Julien; Beaudet, Amélie
    The lateral semicircular canal and its predicted relation to head posture have been used in reconstructions of locomotion and posture of contemporary and extinct species, and in the evolution of bipedalism. Inferences of head posture in fossil species sometimes assume that the lateral semicircular canal is held near the earth’s horizontal when the head is at rest. Despite the physiological importance of the vestibular system, the relationship between head posture and lateral semicircular canal orientation in primates has not been explored on a statistically significant sample, using phylogenetically corrected methods. This study tests the hypothesised relationship between lateral semicircular canal orientation and head posture in primates, and investigates potential links to locomotor categories. This study finds that lateral canal orientation is not significantly correlated to positional repertoires. Significant differences in canal orientation are detected between terrestrial and arboreal species. Neutral head posture distinguishes several locomotor categories, and explains a moderate proportion of the variance in positional behaviour. Brain mass is found to correlate with positional behaviour when correcting for the effects of the phylogeny. The implications of the evolution of head posture in fossil species are discussed.
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    Craniomandibular anatomy of the akidnognathid therocephalian Olivierosuchus parringtoni from the Early Triassic of South Africa
    (Evolutionary Studies Institute, 2023) Gigliotti, Alessandro; Pusch, Luisa C; Kammerer, Christian F; Benoit, Julien; Fröbisch, Jörg
    Therocephalians were an ecomorphologically varied and diverse-sized group of therapsids with widespread distribution during the late Permian and earliest Triassic periods. Here, we redescribe the holotype of the therocephalian Olivierosuchus parringtoni (BP/1/3849) from the Early Triassic Lystrosaurus declivis Assemblage Zone in the main Karoo Basin of South Africa. The specimen includes a complete skull, mandible, and the anterior portion of the skeleton. Previously unknown endocranial features are described using high-resolution computed tomography (CT), including internal surfaces of braincase and palatal bones, as well as soft tissue structures such as the brain and inner ear endocasts. Comparisons with closely related therapsids permit a detailed comparative analysis of the brain and inner ear morphology of Olivierosuchus.
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    Dataset from : The lateral semicircular canal and head posture in “ungulate” mammals: implications on diet, behavior and paleobiological reconstructions
    (2020-07-07) Benoit, Julien; Legendre, Lucas; Farke, Andrew; Neenan, James M; Mennecart, Bastien; Costeur, Loic; Merigeaud, Samuel; Manger, Paul
    For over a century, it has been assumed that the plane of the lateral semicircular canal of the inner ear is parallel to the earth horizontal when the head is at rest. This has long been used by paleontologists to reconstruct head posture in extinct species. Thought this hypothesis has been repeatedly questioned, it has never been tested on a large sample size and at a broad taxonomic scale in mammals. This study presents a comprehensive test of this hypothesis in more than a hundred “ungulate” species. Using CT scanning and manual segmentation, the orientation of the skull was reconstructed as if the lateral semicircular canal of the bony labyrinth was aligned with the earth's horizontal plane. This reconstructed cranial orientation was statistically compared to the actual head posture of the corresponding animals using a dataset of 10,000 photographs and phylogenetic regressions. A statistically significant correlation between the reconstructed cranial orientation and head posture is found, although the plane of the lateral semicircular canal significantly departs from the earth's horizontal plane. We thus caution against the use of the lateral semicircular canal as a proxy to infer the horizontal plane on dry skulls and in extinct species. Diet (browsing or grazing) and head-butting behavior are significantly correlated to the orientation of the lateral semicircular canal, but not to the actual head posture. Head posture and the orientation of the lateral semicircular canal are both strongly predetermined by phylogeny
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    Postcranial morphology of the South African middle Permian pareiasaurs from the Karoo Basin of South Africa
    (Evolutionary Studies Institute, 2021-05-28) van den Brandt, Marc J.; Benoit, Julien; Abdala, Fernando; Rubidge, Bruce S.
    Pareiasaurs were relatively abundant and globally distributed herbivorous parareptiles of the middle to late Permian. The basal-most pareiasaurs, the Bradysauria, are restricted to the middle Permian of South Africa and went extinct at the end of the Guadalupian (Capitanian) at the top of the Tapinocephalus Assemblage Zone. Currently, three genera are recognized in this group: Bradysaurus, Embrithosaurus and Nochelesaurus, but their postcrania are poorly known, and consequently poorly understood. In this paper, our third contribution designed to improve understanding of the Bradysauria, we present a detailed comparative postcranial description and updated diagnoses for Bradysaurus baini, Embrithosaurus schwarzi and Nochelesaurus alexanderi. Bradysaurus baini has one postcranial autapomorphy: anterior dorsal osteoderms smooth and strongly convex, with an incipient central boss, and very light ornamentation. Three pelvic autopomorphies of Embrithosaurus schwarzi are confirmed: anterior portion of the iliac blades flat and vertical (not everted or upturned); iIiac blades diverge anteriorly, oriented at 45–60° off the sagittal plane; and a very thick pelvic symphysis. For Nochelesaurus alexanderi we remove all three of the postcranial autapomorphies previously proposed. To the diagnoses of each species, we have added several new distinguishing postcranial features, within the local group of middle Permian pareiasaurs. The results reinforce our previous cranial studies concluding that three valid species of pareiasaurs are represented in the South African middle Permian.
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    Reassessment of the Phylogeny of Basal Therapsida Using Micro-Tomography and Bayesian Phylogeny
    (University of the Witwatersrand, Johannesburg, 2023) Duhamel, Alienor; Rubidge, Bruce; Benoit, Julien
    This PhD research is focussed on the evolution and cranial anatomy of the earliest therapsids. The Therapsida is a paraphyletic group of land tetrapods that lived mostly during the Permian and Triassic Periods. They emerged quite suddenly in the fossil record during the middle Permian, already showing diversification into five distinct groups: Biarmosuchia, Dinocephalia, Anomodontia, Gorgonopsia and Therocephalia. A sixth group, the Cynodontia, appeared during the late Permian. Of these, the anomodonts, therocephalians, and cynodonts survived the devastating Permo-Triassic mass extinction and continued to be the dominant tetrapods during the Early and Middle Triassic Periods. Ultimately, the cynodonts would evolve into the earliest mammals. Chapter 1 introduces the scientific questions tackled in this thesis. Chapter 2 provides the necessary explanations about the material and methods used for this work. The use of CT-scanning technology allows for the detailed examination of cranial internal morphology, with the goal of incorporating inner cranial characters into a phylogenetic framework. Chapters 3 and 6 focus on the fossilisation gap at the early to middle Permian transition, which has led to debates over the timing of the early diversification of the Therapsida. In Chapter 3, the geologic position and anatomy of one of the oldest known therapsids, Raranimus dashankouensis is reviewed. The chapter concludes with a reassessment of the basal phylogenetic position of Raranimus and suggests a Roadian origin for the taxon. Chapter 6 presents a comprehensive analysis of cranial morphological characters based on the descriptions and findings from Chapters 3, 4, and 5. Using both traditional maximum parsimony and clock-based Bayesian inference of phylogeny for the first time on the Therapsida, the results suggest that therapsids originated around 280.5 million years ago and rapidly diversified into several distinct clades during the Kungurian and Roadian Epochs. The phylogenetic relationships of several taxa are reevaluated and the findings suggest that Biseridens is more closely related to the Dinocephalia and Biarmosuchia, rather than the Anomodontia. Furthermore, the results suggest that Sinophoneus may represent the basal-most dinocephalian, and that Therocephalia might be paraphyletic. Therapsids were characterised by a wide range of cranial morphologies, with the Biarmosuchia and Anomod ontia exhibiting distinct cranial features. Both groups are considered basal among therapsids. Chapter 4 of this PhD research focuses on the postnatal ontogenetic development of cranial ornamentation in Biarmosuchia and possible impact on phylogeny. The results suggests that cranial bosses and ridges are ontogenetic features and the parietal bone originates from multiple centres of ossification. Chapter 5 is a comprehensive cranial description of several basal anomodont specimens. The Chapter concludes with a review of the taxonomy of the genus Eodicynodon and proposes the creation of a new taxonomical unit for specimen NMQR 2913.
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    Synchrotron scanning reveals the deep evolutionary root of the mammalian brain: the surprisingly advanced endocast morphology of Lumkuia fuzzi (Cynodontia: Probainognathia)
    (2023-07) Benoit, Julien
    The mammalian brain is very distinctive for its large relative size, enlarged olfactory bulbs, and layered isocortex. These defining traits likely evolved in the non-mammalian probainognathian cynodonts, although the timing and exact phylogenetic sequence in which these characters evolved is not well understood. The endocast of the brain cavity provides a unique window into the evolution of the central nervous system of extinct species. The endocast of the basal-most probainognathian, Lumkuia fuzzi, is here described for the first time. Its olfactory bulbs are relatively large despite that its encephalization quotient is lower than in Mammaliaformes. This contradicts the consensually established hypothesis that encephalization and olfaction evolved in concert. Moreover, the data presented here do not indisputably distinguish between the encephalization quotients of Mesozoic mammals, non-mammalian mammaliaforms, and non-mammaliaform cynodonts, which suggests that brain enlargement was gradual in this lineage. Lumkuia also possesses marked cerebral hemispheres, which is traditionally interpreted as the sign of the presence of an isocortex and hair. The enlarged olfactory bulbs and cerebral hemisphere in Lumkuia strongly support that the defining features of the mammalian brain began evolving in the last common ancestor of the Probainognathia clade, as early as the early Anisian.