Osteology of Rauisuchus tiradentes from the Late Triassic (Carnian) Santa Maria Formation of Brazil, and its implications for rauisuchid anatomy and phylogeny

Abstract

As the eponymous type species for rauisuchians, Rauisuchus tiradentes von Huene, 1938 represents an important but inadequately known specimen. The revision of the type material from the Upper Triassic (Carnian) Santa Maria Formation of Brazil reveals new anatomical data and previously unrecognised characters, including three new possible autapomorphies: a knob-like thickening on the base of the posterior process of the premaxilla; short and ventrally keeled cervicals lacking postzygodiapophyseal laminae; and mid-caudal vertebrae with an accessory neural spine and a postspinal lamina. Several elements are re-identified, including a postorbital (originally identified as postfrontal) and a pterygoid (originally identified as a prefrontal), and additional material from a secondary fossil site, originally assigned to R.tiradentes, including a left ilium, is excluded. Based on the recovered information and new morphological data, the systematic position of R.tiradentes is tested in a comparison of two phylogenetic reanalyses. Both analyses differ in respect to the phylogenetic position of R.tiradentes, and recover 'rauisuchians' as a paraphyletic assemblage of non-crocodylomoprh archosaurs.