A new elasmosaurid plesiosaur from the lower Cretaceous of Queensland, Australia

Abstract

A nearly complete but badly crushed elasmosaurid plesiosaur skull is described from the Upper Albian Toolebuc Formation of northern Queensland, Australia. The specimen has a long history, being previously referred to the Australian Aptian genus ‘Woolungasaurus’ (considered a nomen dubium), as well as provisionally to Elasmosauridae gen. et sp. nov., and most recently to Tuarangisaurus (Campanian-Maastrichtian, New Zealand and potentially Patagonia). The present assessment alternatively proposes assignment to a new taxon, Eromangasaurus carinognathus, gen. et sp. nov., uniquely characterized by the presence of seven premaxillary teeth (three lateral pairs, one midline), an elongate mandibular symphysis with prominent ventral midline keel, and a combination of osteological features variably developed in other elasmosaurids. Cladistic analysis using 43 discrete cranio-dental and vertebral characters coded for 16 ingroup and one outgroup taxon supports this conclusion, indicating that E. carinognathus is a crown-group elasmosaurid of more derived grade than Occitanosaurus (Lower Jurassic, Toarcian, France). Affinities with other Cretaceous elasmosaurids are poorly resolved. Nevertheless, a close relationship with Tuarangisaurus is not substantiated; instead, E. carinognathus forms a discrete clade with Terminonatator (Campanian, Canada).