A new desmatosuchine aetosaur (Archosauria : Suchia) from the Upper Triassic Tecovas Formation (Dockum Group) of Texas

摘要

A small aetosaur skeleton collected in 1939 front the Tecovas Formation of Texas and assigned to Desmatosuchus is reassigned to it new taxon. Sierritasuchus macalpini. Phylogenetic analysis suggests that Sierritasuchus is at member of the Desmatosuchinae. It can tic distinguished front other desmatosuchines by two autapomorphies: (1) recurved spines on the lateral plates that are triangular in cross-section with a sharply ridged anterior edge: and (2) the presence of a sharp, ventrally oriented ridge oil the posterior faces of the dorsal eminences of the paramedian plates, as well as it unique combination of characters including the presence of an anterior bar oil the paramedian and lateral plates, a random pattern of ornamentation on the paramedian plates. and it dorsal eminence that contacts the posterior plate margin of the paramedian plates. Histological study of the holotypic plates ill combination with comparison to a growth Series in Typothorax, and size-independent growth indicators such its neurocentral sulture closure suggests that the specimen is neither a young juvenile nor a fully grown adult, The recognition of morphologically distinct specimens such its the holotype and referred material of Sierritasuchus demonstrates that past practices of assigning aetosaur specimens to known taxa based on superficial resemblance has masked diversity in this clade. Voucher specimens for biochronologic and biogeographic analyses should lie carefully investigated before being used for such studies.