Description of new and re-examination of previously described cranial remains of Prolacerta broomi Parrington allows reappraisal of the structure of the skull in this basal archosauromorph reptile. The ventral margin of the premaxilla is slightly deflected, and there is a relatively large lateral foramen in the maxilla that is bounded anteriorly by the premaxilla; both features are shared with the basal rhynchosaur Mesosuchus and the basal archosauriform Proterosuchus. Implantation of the marginal dentition is ankylothecodont: the teeth are rooted relatively deeply, bounded lingually by a deep wall of the jaw, and anchored to the jaw by bone of attachment. The pineal foramen varies in size from little more than a scar in the interparietal suture to a suboval opening several millimetres in diameter. Contrary to previous claims, the skull roof in Prolacerta was akinetic and quadrate mobility (streptostyly) was absent. Phylogenetic analysis of a previously published data matrix, modified by the addition of new anatomical data and reinterpretation of some characters, corroborates the hypotheses of the polyphyly of Prolacertiformes (Protorosauria) and of a close relationship between Prolacerta and Archosauriformes.

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The initial stages of evolution of Diapsida (the large clade that includes not only snakes, lizards, crocodiles and birds, but also dinosaurs and numerous other extinct taxa) is clouded by an exceedingly poor Palaeozoic fossil record. Previous studies had indicated a 38 Myr gap between the first appearance of the oldest diapsid clade (Araeoscelidia), ca 304 million years ago (Ma), and that of its sister group in the Middle Permian (ca 266 Ma). Two new reptile skulls from the Richards Spur locality, Lower Permian of Oklahoma, represent a new diapsid reptile: Orovenator mayorum n. gen. et sp. A phylogenetic analysis identifies O. mayorum as the oldest and most basal member of the araeoscelidian sister group. As Richards Spur has recently been dated to 289 Ma, the new diapsid neatly spans the above gap by appearing 15 Myr after the origin of Diapsida. The presence of O. mayorum at Richards Spur, which records a diverse upland fauna, suggests that initial stages in the evolution of non-araeoscelidian diapsids may have been tied to upland environments. This hypothesis is consonant with the overall scant record for nonaraeoscelidian diapsids during the Permian Period, when the well-known terrestrial vertebrate communities are preserved almost exclusively in lowland deltaic, flood plain and lacustrine sedimentary rocks.

The cranial osteology of the aquatic reptile Mesosaurus tenuidens is redescribed on the basis of new and previously examined materials from the Lower Permian of both southern Africa and South America. Mesosaurus is distinguished from other mesosaurs in exhibiting an absolutely larger skull and possessing relatively longer marginal teeth. The teeth gradually angle outwards as one progresses anteriorly in the tooth row and become conspicuously procumbent at the tip of the snout. The suggestion that mesosaurs used their conspicuous dental apparatus as a straining device for filter feeding is based upon erroneous reconstruction of a high number of teeth in this mesosaur. Reinterpretation of the morphology and the organization of the marginal teeth of Mesosaurus suggests that they were used to capture individually small, nektonic prey. General morphological aspects of the skull support the idea that Mesosaurus was an aquatic predator and that the skull was well adapted for feeding in an aqueous environment. The anatomical review permits critical reappraisal of several cranial characters that have appeared in recent phylogenetic analyses of early amniotes. Emendation of problematic characters and reanalysis of amniote phylogeny using a slightly modified data matrix from the literature strengthens the hypothesis that mesosaurs form a clade with millerettids, procolophonoids and pareiasaurs within Reptilia.

A 251 million year old partial burrow cast containing an articulated skeleton of the mammal-like carnivore Thrinaxodon liorhinus is the oldest evidence for burrowing by a cynodont synapsid. The burrow cast comes from terrestrial flood plain sediments close to the Permian-Triassic boundary in the Karoo of South Africa. Together with those of the later cynodont Trirachodon, the Thrinaxodon burrow cast indicates that burrow-making was broadly distributed in basal synapsids and has a long history in non-mammalian synapsid evolution. A reconstruction of its appendicular skeleton in cross-section indicates that Thrinaxodon was able to adopt a facultatively mammalian stance within its burrow shaft. Burrows of cynodont design are more common in Triassic rocks than previously realized, and suggest that burrowing may represent an adaptive response by cynodonts to the environmental conditions associated with the mass extinction event that punctuated the end of the preceding Permian period. The widespread occurrence of burrowing among extant mammals implies that the ancient synapsid ability to burrow conferred a strong adaptive value in the evolution of Mammalia.

A new specimen from the base of the Beaufort Group, Upper Permian of South Africa, represents a new therapsid (`mammal-like reptile') which has been identi¢ed as the most basal (`primitive') member of the Anomodontia. Anomocephalus africanus gen. et sp. nov. is based upon a partial skull that exhibits several characteristic anomodont synapomorphies including the presence of isodont marginal teeth and a dorsally bowed zygoma, but is distinguished from other anomodonts by the possession of peg-like marginal dentition with oblique wear facets on the tips of the teeth. Anomocephalus is excluded from a clade comprised of all other anomodonts as (i) the snout is relatively long, (ii) the vertically aligned zygomatic process of the squamosal is blade-like, and (iii) the squamosal does not contact the ventral tip of the postorbital. The basal position of Anomocephalus, together with its South African occurrence, strongly supports the postulate that a Gondwanan distribution was ancestral for anomodonts.

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A reappraisal of the eggshell of ratites clarifies aspects of its microstructure and ultrastructure. The phylogenetic usefulness of the eggshell data, consisting of discrete characters, is assessed using eggshell characters alone and by adding the eggshell characters to a data matrix from the literature based on skeletal characters. The resultant tree from the eggshell data alone yields Apteryx as the most basal ratite, dinornithids as the sister taxon of a clade of large living ratites, with Casuarius and Dromaius in a sister-group relationship. The combined eggshell and skeletal analysis revealed most groupings within Ratitae that were based on previous cladistic analysis of the skeletal characters alone, but also supports two equally parsimonious topologies: one identifies Dinornithidae and Apteryx as a clade at the base of Ratitae, and the other identifies Apteryx as the sister taxon of a clade consisting of all the other ratites. It is determined that the characteristics used to define the improperly named "ratite morphotype" in the current eggshell parataxonomy are not synapomorphies of the eggshell of Ratitae. An expanded cladistic analysis of the eggshells of avian and non-avian theropods is required to determine the phylogenetic usefulness of the characteristics of the ratite morphotype.