Limb anatomy of the Triassic turtles: appendicular osteology of Proterochersis (Testudinata, Proterochersidae)

Abstract The turtle locomotor system is heavily modified owing to the severe impact of development of the shell on the body plan of these reptiles. Although limb and girdle osteology of the earliest, Triassic turtles is relatively well understood in general, the exact impacts of variability, ontogeny and preservation (e.g. deformation) on the observed morphologies have rarely been considered in detail. Here, we describe in detail and document the osteology and intraspecific variability of the limbs and girdles of Proterochersis spp., the basalmost true turtles (Testudinata). We also provide a synthesis of currently available data and detailed comparisons with other Triassic stem turtles to gain a better understanding of the diagnostic value of the early turtle appendicular skeleton and to pave the way for future biomechanical and functional studies. Our data suggest that Proterochersis spp. could be at least partly aquatic and could change their preferred habitat during ontogeny, with larger (and, presumably, older) specimens presenting more characters suggestive of a more terrestrial environment.