A new aetosaur from the Upper Triassic Chinle Formation of the Eagle Basin, Colorado, USA
Bryan J. Small, Jeffrey W. Martz, 2013. "A new aetosaur from the Upper Triassic Chinle Formation of the Eagle Basin, Colorado, USA", Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin, S. J. Nesbitt, J. B. Desojo, R. B. Irmis
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A small aetosaur skull and skeleton and referred material from the Chinle Formation, Eagle Basin of Colorado, USA, is described as a new taxon, Stenomyti huangae gen. et sp. nov, distinguished from other aetosaurs by the following autapomorphies: three premaxillary teeth; four palpebrals; pronounced midline ridge on frontals and parietals; paired ridges flanking midline ridge on parietal and frontal; exclusion of quadratojugal from ventral margin of skull by contact between jugal and quadrate; exclusion of postorbital from infratemporal fenestra; infratemporal fenestra a horizontally oriented oval that embays the posterior edge of the jugal; retroarticular process longer than distance between articular glenoid and posterior edge of external mandibular fenestra; oval to irregularly shaped ventral osteoderms that do not contact each other. Paramedian and lateral osteoderms of S. huangae are nearly identical to those of Aetosaurus ferratus, and other shared cranial characters suggest that these taxa are closely related and lie outside the clade Typothoracisinae + Desmatosuchinae. This discovery indicates that other reports of Aetosaurus across Laurasia based on osteoderms should be reassessed. Similar confusion with the osteoderms of other non-typothoracisine/desmatosuchine aetosaurs such as Aetosauroides, Stagonolepis and Calyptosuchus suggests that osteoderms are not always reliable taxonomic indicators.
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Archosaurs, an important reptile group that includes today’s crocodiles and birds, arose during the Triassic in the aftermath of the greatest mass extinction of all time. In the last 20 years, our understanding of the early evolution of the group has improved substantially with the discovery of new fossils and species of early archosaurs and their closest relatives, a better understanding of the relationships of these animals, and new insights into their palaeobiology. In order to synthesize these new data, researchers of early archosaurs from around the world met at the first symposium of early archosaur evolution at the IV Congreso Latinoamericano de Paleontología de Vertebrados (September 2011) in San Juan, Argentina. This symposium facilitated collaboration and strove to paint a better understanding of these extraordinary animals. The resultant body of work is a state-of-the-art examination of early archosaur groups and their close relatives including historical, anatomical, biogeographical, evolutionary and palaeobiological data. This contribution furthers our knowledge of the anatomy, relationships, and palaeobiology of species-level taxa as well as more global patterns of archosaur evolution during the Triassic.