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A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2015. / Thrinaxodon liorhinus, a cynodont that has been of captivating importance in the evolution of therapsids, is one of the best known transitional fossil taxa from non-mammaliaform cynodonts to mammals. The species is abundant in the South African Karoo Basin and is one of the best represented taxa immediately after the Permian-Triassic mass extinction. One of the key adaptive characteristics that may have aided in their survival was fossorialism. Numerous fossils of Thrinaxodon have been found in burrows or in a curled-up position, which has provided important circumstantial evidence for the formalization of the hypothesis of Thrinaxodon as a burrower. However, finding a fossil inside a burrow or even in a curled-up position only provides firm evidence for burrow use, not for burrow creation. Direct evidence for burrowing capability can come from the understanding of the functional morphology of Thrinaxodon limbs. The present study investigates internal and external structure of the Thrinaxodon forelimb, a variety of reptiles characterized by different behavioural patterns, and other cynodonts in order to advance present knowledge about the functional morphology of the transitional phase cynodont. The study uses Geometric Morphometric analyses, forelimb metric indices, torsion and cortical thickness of humeri in order to determine the extent to which, the Thrinaxodon forelimb functionally and structurally resembles that of a fossorial mammal versus a digging reptile. Results of the study tease apart the extent to which the Thrinaxodon forelimb illustrates modifications due to gait (e.g., sprawling versus semi-sprawling) versus a fossorial lifestyle. This would indicate that Thrinaxodon retained the reptilian skeletal configuration and adapted a posture that had begun to resemble parasagittal more than sprawling or semi-sprawling gait. Nonetheless, Thrinaxodon exhibits forelimb structural similarities to digging species, whether mammals or reptiles.

The genus Kannemeyeria is one of the most important and distinctive taxa of the Triassic dicynodonts. It became the first Triassic dicynodont known to science, and thus forms the benchmark for the comparison of the evolution and morphology of other Triassic dicynodonts. An understanding of this genus forms an integral part of the biozonation of the Beaufort Group, and is pivotal in influencing the interpretation of the evolution, physiology and phylogenetic relationships of the Triassic dicynodonts. This study focuses on the detailed cranial morphology and relationships of the Kannemeyeria, and uses a rigorous morphological investigation as the basis for a meaningful elucidation of the functional and thus physiological aspects of this dicynodont. The descriptions demonstrate that variations related to the skull size, distortion or naturally occurring variation within the genus allow for the synonymy of the formerly recognised species K. latifrons Broom (1898; 1913), K. erithrea Haughton (1915) and K. wilsoni Broom (1937). This conclusion is further supported by the allometric analysis which cannot distinguish the variation observed in the holotypes with that occurring naturally within a growth series. Apart from the large specimen, the other smaller individuals are accommodated in the genus as different ontogenetic stages of the growth series represented by K. simocephalus Weithofer (1888). Several allometric variables show unusual patterns of development, indicating that Kannemeyeria can be subdivided into ontological classes, as juvenile and adult forms, separated from each other by a particular level of development. An age-related threshold level is suggested, and considered to represent an animal reaching sexual maturity. It is consequently proposed that the Kannemeyeria population was, at an age-related level, subdivided into sexually mature and immature groups but remained ecologically homogeneous. Both the descriptions and the allometric analysis of the species K. cristarhynchus Keyser & Cruickshank (1979) clearly indicate that it does not conform to the growth series of K. simocephalus and thus the differences observed between these two taxa are not constrained to size increases. Consequently, the recognition of the species K. cristarhynchus is considered valid. From the observations of the cranial morphology, tested using an allometric analysis, generic and specific diagnoses are constructed for Kannemeyeria and its two African species. Several features of Kannemeyeria are discussed in a functional context. A corrugated hom-covered snout and large caniniform processes are considered to be associated with defence and posturing behaviour. Several features of the braincase also suggest herding behaviour. Kannemeyeria also has a slightly different occipital musculature arrangement than that proposed for many other dicynodonts. Most Kannemeyeria cranial features are related to its masticatory function. From the analysis of masticatory cycle it is clear that the jaw action is described via a single pivot-point, which in Kannemeyeria approached the original, primitive position of the jaw hinge. The vertical orientation of the articulation and this pivot-point ensured that the muscle action during second phase of mastication produced an upward crushing and grinding action instead of the typical fore-and-aft motion of many other dicynodonts. It also meant that the muscle force was at their maximum, and little or no energy was lost to translation of the moment arm at the jaw articulation. Consequently, the Kannemeyeria masticatory cycle was both highly effective and extremely efficient. The morphology, and resultant physiology, of Kannemeyeria skull is considered to represent the innovative foundation for much of the success of many of the later Triassic dicynodonts.

Mixosaurid ichthyosaurs (mixosaurs) are a dominant group of Middle Triassic marine reptiles that was widely distributed in both Tethyan and Panthalassic terranes. They are represented by many excellently preserved specimens from all around the world and have been studied for more than one hundred years. Even so, their morphology is not adequately known. The systematics of mixosaurs is not well understood and their phylogeny has been controversial. The nomination of several Chinese mixosaurs makes the situation even worse. This thesis aims to provide a comprehensive review of Chinese mixosaurs and discuss their phylogenetic relationships. The detailed anatomy of only valid Chinese mixosaurid species Mixosaurus panxianensis is well established in this thesis. Its ontogenetic changes are also noted and a better diagnosis is given. A new morphotype of mixosaurs from a recently discovered fossil Lagerst?tte, the Luoping biota, is described in detail. This morphotype is similar to M. panxianensis but consistent differences are also present. The ecological comparison to M. panxianensis demonstrates that this morphotype represents a new taxon that is different from M. panxianensis. A nearly complete and articulated specimen of Phalarodon atavus from the Middle Triassic Luoping biota, Yunnan, South China is described. This is the first specimen of P. atavus discovered outside the Germanic Basin. The discovery of this specimen demonstrates a cosmopolitan distribution of P. atavus across the whole Tethyan ocean. The new specimen is also the first one preserving the postcranial anatomy of this species, providing the potential to evaluate its swimming ability for the first time. Functional morphology shows that this species is well adapted for a pursuit attack of prey, consistent with the distribution pattern of the species. Tooth crown morphology suggests that P. atavus may prefer externally soft prey such as belemnoids. Mixosaurs are divided into three ontogenetic stages based on the humeral morphology. The juvenile stage is characterized by a textured dorsal humeral shaft surface. The subadult stage is characterized by a smooth humeral shaft in dorsal view with a rugose humeral head. The adult stage is characterized by a smooth humeral head. The consistent presence of the surface texture of ventral humeral shaft is most probably caused by the strong muscle insertion presumably related to the function of steering of the fore fins in mixosaurs. Five morphotypes of Chinese mixosaurs are recognized in this study. Twenty-five more or less new characters are introduced to evaluate the phylogenetic relationships of mixosaurian-like specimens from China. The monophyly of mixosaurs including all studied Chinese morphotypes is well corroborated. Further investigation on the mixosaurs from Monte San Giorgio is recommended to resolve the phylogenetic relationships of mixosaurs. / published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

A Dissertation submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the requirements for the Degree of Master of Science Johannesburg, 2015 / The Chiniquodontidae is a family of Triassic carnivorous cynodonts well represented in the Middle-Upper Triassic of Argentina and Brazil. Chiniquodontids were more recently discovered in Madagascar and central Namibia, representing the only record of the family outside South America. The Namibian specimen was discovered in the Upper Omingonde Formation and is represented by the skull and a partial skeleton. The new chiniquodontid was identified as Chiniquodon and is diagnosed by the postcranial characteristics identified; a strong bend in the proximal portion of thoracic ribs, reduced curvature of the clavicle, although this may be due to deformation, robustness of the neck of the ilium, differences in the angulation between the edge of the posterior lamina of the ilium and the margin of the neck, and a large ischium, which is more than twice the size of the pubic plate. The postcranial material of the chiniquodontid from Namibia is described and compared with that of South American chiniquodontids. Chiniquodontids lack costal plates on ribs, show a tall and slender scapular blade, a large acromion process positioned well above the scapular neck and absence of disc-like phalanges in the autopodium. The Namibian Chiniquodon provides the first evidence of elements from the pes in chiniquodontids, and one of the few for non-mammaliaform cynodonts. Sedimentological studies confirm that the Upper Omingonde Formation of Namibia represents fluvial deposits of braided and meandering rivers formed in a predominately arid climatic regime during the Middle Triassic.

Keichousaurus hui Young, 1958, from the Middle Triassic of Guizhou, China is a small sauropterygian reptile. It has short snout and elongated temporal openings resembling the European pachypleurosaurid Dactylosaurus. Unlike all the other sauropterygians, the parietal opening is anteriorly positioned. The neck is long and flexible. The body is rigid and the bones are pachyostotic. It has two or three sacral vertebrae. The most striking feature of Keichousaurus is its broad ulna. The entire forelimb has the outline of a paddle or an oar, and may have functioned like one. There is noticeable sexual dimorphism, as is the case for Alpine pachypleurosaurids. The growth of the humerus is highly positive allometric, indicating an important role of the forelimb in locomotion. The horizontal orientation of the pectoral girdle indicate that Keichousaurus, as well as other pachypleurosaurids, was not a subaquatic flyer. Instead, a drag-based regime was followed in locomotion. The symmetrical rowing of the forelimbs precludes lateral undulatory movement of the body. However, vertical undulation is theoretically possible. The reassessment of the phylogenetic position of Keichousaurus hui confirmed that it is a member of the monophyletic group Pachypleurosauroidea.

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No description available.

The osteology of the Upper Triassic podokesaurid Syntarsus rhodesiensis is described, based on a series of 30+ individuals representing all skeletal elements, recovered since the description of the holotype (Raath, 1969). A brief account of the geology of the finds is given, with an attempt at a reconstruction of the palaaoenvironment. The excellence of preservation of the bones has permitted an attempt at the restoration of soft tissues including the brain, cranial nerves, main cranial blood vessels and the musculature of the jaws, neck and limbs. Histological sections of limb bones have shown that the compact bone was highly vascular, and this, together with the structure of the brain, palaeoenvironmental considerations, social behaviour and group structure, leads to the conclusion that Syntarsus was an endothermic homeotherm inhabiting a hot arid region at the end of the Triassic, with a social organisation into "flocks" in which females predominated numerically. Clear evidence of sexual dimorphism is presented. Syntarsus is reconstructed as a bipedal, saltatorial predator which differs in subtle, but probably generically significant, characteristics from the closely related North American genus, Coelophysis. Its anatomy characterises it as a medium-sized agile animal with a highly kinetic skull; incipiently opposable pollex in the raptorial manus; highly cursorial hindlimb; and with features in the dentition and hallux which suggest a grooming function. It is concluded that the Triassic coelurosaurian stock provided an advanced and well adapted base from which the successful coelurosaur radiation into the later Mesozoic sprang, and that this stock was physiologically pre-adapted for the emergence of the avian (and possibly the pterosaur) lineages in the Jurassic

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