The appendicular osteology of the Early Jurassic theropod Piatnitzkysaurus floresi and its implications on the morphological disparity of non-coelurosaurian tetanurans

Abstract

Piatnitzkysaurus floresi is a theropod dinosaur from the Cañadón Asfalto Formation (Chubut Province, Argentina) and one of the few Early Jurassic tetanurans known worldwide. This species is known from two specimens and plays a key role in our understanding of the early evolution of tetanuran theropods. Nevertheless, the published information about its postcranium is limited to the original description of the 1980s and drawings in a few views. Here, we redescribe in detail the appendicular skeleton of Piatnitzkaysaurus and integrate new information into new phylogenetic and morphological disparity analyses focused on non-coelurosaurian tetanurans. Our results agree with recent studies that place Piatnitzkysauridae (including Condorraptor, Marshosaurus, Piatnitzkysaurus, and Xuanhanosaurus) as the earliest diverging group of Allosauroidea and within a monophyletic Carnosauria (Allosauroidea + Megalosauroidea). Morphological disparity analyses of the appendicular skeleton of non-coelurosaurian tetanurans show that the Jurassic species occupy a different morphospace from the Cretaceous species. Condorraptor and Piatnitzkysaurus are found within the morphospace occupied by the Middle Jurassic species from the Northern Hemisphere, which indicates the presence of similar body plans for the non-coelurosaurian tetanurans during the Early–Middle Jurassic worldwide. The new information about Piatnitzkysaurus improves our knowledge about the evolution of early tetanurans.