New heterodontosaurid remains from the Cañadón Asfalto Formation: cursoriality and the functional importance of the pes in small heterodontosaurids

Abstract

New ornithischian remains reported here (MPEF-PV 3826) include two complete metatarsi withassociated phalanges and caudal vertebrae, from the late Toarcian levels of the Cañadón Asfalto Formation.We conclude that these fossil remains represent a bipedal heterodontosaurid but lack diagnostic characters to identifythem at the species level, although they probably represent remains of Manidens condorensis, known from the samelocality. Histological features suggest a subadult ontogenetic stage for the individual. A cluster analysis based onpedal measurements identifies similarities of this specimen with heterodontosaurid taxa and the inclusion of thenew material in a phylogenetic analysis with expanded character sampling on pedal remains confirms the describedspecimen as a heterodontosaurid. Finally, uncommon features of the digits (length proportions among nonungualphalanges of digit III, and claw features) are also quantitatively compared to several ornithischians, theropods, andbirds, suggesting that this may represent a bipedal cursorial heterodontosaurid with gracile and grasping feet and longdigits. In particular, the elongated non-terminal pedal phalanges and morphology of digit III resemble features presentin arboreal birds, a unique condition found so far among ornithischians.