Sarmatosuchusand the early history of the Archosauria

A detailed description of the early archosaur Sarmatosuchus otschevi Sennikov, 1994, from the Middle Triassic Donguz Formation of southern European Russia, is presented. New morphological data forms the basis of a preliminary investigation of the phylogenetic relationships between a selection of the earliest archosaurs. A parsimony analysis based on 9 taxa and 35 characters recovers two most parsimonious trees that support the referral of Sarmatosuchus and Fugusuchus to a proterosuchid clade, as well as the paraphyly of the Proterosuchia. Characters from the structure of the braincase are more homoplastic than those from the rest of the skeleton. The presence of Sarmatosuchus in the Middle Triassic affords evidence that the proterosuchids were a more diverse and persistent clade than has been previously envisaged. Evidence suggesting that proterosuchids may have existed with erythrosuchids and early crown-group archosaurs in the Middle Triassic requires a revision of our understanding of the early part of the archosaurian radiation.