Restudy of the unique diapsid reptile Mesosuchus browni Watson, from the Cynognathus Assemblage Zone (late EarlyTriassic to early MiddleTriassic) of the Burgersdorp Formation (Tarkastad Subgroup; Beaufort Group) of South Africa, con¢rms that it is the most plesiomorphic known member of the Rhynchosauria. A new phylogenetic analysis of basal taxa of Archosauromorpha indicates that Choristodera falls outside of the Sauria, Prolacertiformes is a paraphyletic taxon with Prolacerta sharing a more recent common ancestor with Archosauriformes than with any other clade, Megalancosaurus and Drepanosaurus are sister taxa inthe clade Drepanosauridae within Archosauromorpha, and are the sister group to the clade Tanystropheidae composed of Tanystropheus, Macrocnemus, and Langobardisaurus. Combination of the phylogenetic relationships of basal archosauromorphs and their known stratigraphic ranges reveals signi¢cant gaps in the fossil records of Late Permian and Triassic diapsids. Extensions of the temporal ranges of several lineages of diapsids into the Late Permian suggests that more groups of terrestrial reptiles survived the end-Permian mass extinction than thought previously.Keywords: fossil; phylogeny; reptile; South Africa; diapsid; Gondwana apparent immediately to Robert Broom that the skeletons were actually of two distinct, though related, species (Broom 1913a). Broom designated an articulated skeleton with a single external naris and a pair of supposed acrodont premaxillary teeth as the type of Mesosuchus, and the remainder of the specimens were assigned to a new genus and species Euparkeria capensis. Watson's confusion is understandable given that the specimens he examined consisted only of an incomplete skull and articulated postcranium, numerous isolated cranial elements lacking from the single skull, and various parts of the axial and appendicular skeletons that could not be compared readily with the single, imperfect skeleton.As the etymology of the name suggests, Watson (1912a) believed that Mesosuchus was an ancestral crocodile with close a¤nities to other presumed primitive crocodilians such as Proterosuchus, Erythrosuchus and Ornithosuchus. However, it is clear that the data for this opinion were derived from the skeletons of Euparkeria, in particular the slender lower jaw with thecodont implantation, the crocodilian-like ilium, and the construction of the tarsus and pes. Broom (1913a) recognized the great resemblance of Mesosuchus to the diaptosaurian (basal diapsid) reptile Howesia also from the Cynognathus Assemblage Zone near Aliwal North (Broom 1906). He concurred with Watson on the close relationship between Ornithosuchus and Euparkeria. In the same year, Broom (1913b) gave a more detailed description of both Euparkeria and Mesosuchus, rea¤rming the a¤nities between Euparkeria and pseudosuchians, and between Mesosuchus and other rhynchocephalians such as Howesia, Rhynchosaurus and Hyperodapedon.In 1921, the fossil collection of Mr Alfred Brown was purchased by the South African Museum, and a second ...

Musculature of the pectoral and pelvic appendages and girdles of adult and nestling Maiasaura peeblesorum (Dinosauria: Ornithischia: Hadrosauridae) from the Late Cretaceous of Montana is restored according to a phylogenetically based methodology. This methodology uses an explicit, independently derived phylogenetic hypothesis of the fossil taxon and related extant taxa to generate a series of inferences regarding the presence of a muscle, its number of components, and the origin(s) and insertion(s) of these components. Corroborative osteological evidence is sought on the fossil in the form of scars and processes that fulfill the criteria for muscular attachment according to generalisations based upon extant vertebrates. A total of 46 muscles are restored, although separate attachment sites for numerous muscles cannot be discerned on the fossils. Osteological evidence for several muscles can be found in nestlings of Maiasaura despite their skeletal immaturity. Results of the phylogenetically based approach and new hypotheses for homologies of deep dorsal thigh muscles suggest that it is more parsimonious to restore the femoral insertions of M. iliofemoralis on the greater trochanter and M. puboischiofemoralis internus on the anterior (lesser) trochanter, a reversal of the traditional interpretation. The often-cited osteological specialisations of birds for flight are not accompanied in all instances by profound myological transformations, and birds must be included in any attempt to restore the myology of extinct dinosaurs.

:  Restudy of skulls and available postcrania of the proterochampsian archosauriform Proterochampsa barrionuevoi from the Ischigualasto Formation (Upper Triassic, Carnian) in the San Juan Province, Argentina, confirms that the genus is diagnosed by autapomorphies that include dermal sculpturing consisting of prominent ridges and nodular protuberances, a large hook‐like lateral projection on the quadratojugal, an antorbital fossa restricted to a depression along the maxilla, lateral expansion of the premaxilla anterior to the premaxilla–maxilla contact, absence of a supratemporal fossa, exclusion of jugal from suborbital fenestra, basal tubera of parabasisphenoid facing ventrally and reaching laterally beyond the basipterygoid process, and a ventral lamina on the angular. Proterochampsa nodosa is a valid species distinguished from P. barrionuevoi by fewer cranial ridges with larger protuberances, relatively smaller supratemporal fenestrae and width of frontals between orbits less than that of the nasals. A phylogenetic analysis supports the monophyly of Proterochampsia consisting of Proterochampsa, Chanaresuchus bonapartei, Gualosuchus reigi, Tropidosuchus romeri and Cerritosaurus binsfeldi. A temporal separation between the two basal proterochampsians with earliest records in the Late Triassic (Proterochampsa and Cerritosaurus) and Chanaresuchus, Gualosuchus and Tropidosuchus in the Middle Triassic indicates hidden proterochampsian diversity in the Middle Triassic.

No abstract