Sterling J. Nesbitt

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Theropods have traditionally been assumed to have lost manual digits from the lateral side inward, which differs from the bilateral reduction pattern seen in other tetrapod groups. This unusual reduction pattern is clearly present in basal theropods, and has also been inferred in non-avian tetanurans based on identification of their three digits as the(More)
Living archosaurs comprise birds (dinosaurs) and crocodylians (suchians). The morphological diversity of birds and stem group dinosaurs is tremendous and well-documented. Suchia, the archosaurian group including crocodylians, is generally considered more conservative. Here, we report a new Late Triassic suchian archosaur with unusual, highly specialized(More)
It has generally been thought that the first dinosaurs quickly replaced more archaic Late Triassic faunas, either by outcompeting them or when the more archaic faunas suddenly became extinct. Fossils from the Hayden Quarry, in the Upper Triassic Chinle Formation of New Mexico, and an analysis of other regional Upper Triassic assemblages instead imply that(More)
BACKGROUND Archosaurs (birds, crocodilians and their extinct relatives including dinosaurs) dominated Mesozoic continental ecosystems from the Late Triassic onwards, and still form a major component of modern ecosystems (>10,000 species). The earliest diverse archosaur faunal assemblages are known from the Middle Triassic (c. 244 Ma), implying that the(More)
The early evolutionary history of Ornithodira (avian-line archosaurs) has hitherto been documented by incomplete (Lagerpeton) or unusually specialized forms (pterosaurs and Silesaurus). Recently, a variety of Silesaurus-like taxa have been reported from the Triassic period of both Gondwana and Laurasia, but their relationships to each other and to dinosaurs(More)
Characterizing the evolutionary history of early dinosaurs is central to understanding their rise and diversification in the Late Triassic. However, fossils from basal lineages are rare. A new theropod dinosaur from New Mexico is a representative of the early North American diversification. Known from several nearly complete skeletons, it reveals a mosaic(More)
A new discovery of skeletons of Revueltosaurus callenderi from the Upper Triassic Chinle Formation of Petrified Forest National Park, Arizona clearly shows that Revueltosaurus is not an ornithischian dinosaur as previously supposed. Features such as the presence of a postfrontal, crocodile-normal ankle and paramedian osteoderms with anterior bars place R.(More)
The rise of dinosaurs was a major event in vertebrate history, but the timing of the origin and early diversification of the group remain poorly constrained. Here, we describe Nyasasaurus parringtoni gen. et sp. nov., which is identified as either the earliest known member of, or the sister-taxon to, Dinosauria. Nyasasaurus possesses a unique combination of(More)
The Moenkopi Formation has yielded partial and isolated remains of important archosaurs including rauisuchian skull fragments and isolated poposaur centra and pelvic girdle elements. A recently discovered skeleton referable to Arizonasaurus babbitti shows that most of these archosaurian remains belong to one taxon. Characteristics of the skeleton of(More)
The furcula is a structure formed by the midline fusion of the clavicles. This is the element which is unique to theropods and is important for understanding the link between birds and other theropods. New specimens from basal theropods suggest that the furcula appeared very early in theropod history. We review furcula development, function, and morphology,(More)