The osteology of Shuvosaurus inexpectatus, a shuvosaurid pseudosuchian from the Upper Triassic Post Quarry, Dockum Group of Texas, USA.

Abstract

A vast array of pseudosuchian body plans evolved during the diversification of the group in the Triassic Period, but few can compare to the toothless, long-necked, and bipedal shuvosaurids. Members of this clade possess theropod-like character states mapped on top of more plesiomorphic pseudosuchian character states, complicating our understanding of the evolutionary history of the skeleton. One taxon in this clade, Shuvosaurus inexpectatus has been assigned to various theropod dinosaur groups based on a partial skull and referred material and its postcranium was assigned to a different taxon in Pseudosuchia. After the discovery of a skeleton of a shuvosaurid with a Shuvosaurus-like skull and a pseudosuchian postcranial skeleton, it became clear Shuvosaurus inexpectatus was a pseudosuchian. Nevertheless, a number of questions have arisen about what skeletal elements belonged to Shuvosaurus inexpectatus, the identification of skull bones, and the resulting implication for pseudosuchian evolution. Here, we detail the anatomy of the skeleton Shuvosaurus inexpectatus through a critical lens, parse out the bones that belong to the taxon or those that clearly do not or may not belong to the taxon, rediagnose the taxon based on these revisions, and compare the taxon to other archosaurs. We find that Shuvosaurus inexpectatus possesses similar anatomy to other shuvosaurids but parts of the skeleton of the taxon clarifies the anatomy of the group given that they are preserved in Shuvosaurus inexpectatus but not in others. Shuvosaurus inexpectatus is represented by at least 14 individuals from the West Texas Post Quarry (Adamanian holochronozone) and all Shuvosaurus inexpectatus skeletal material from the locality pertains to skeletally immature individuals. All of the skeletons are missing most of the neural arches, ribs, and most of the forelimb. We only recognize Shuvosaurus inexpectatus from the Post Quarry and all other material assigned to the taxon previously is better assigned to the broader group Shuvosauridae.