On the validity of the antarctic ankylosaur antarctopelta oliveroi (Dinosauria, Ornithischia)

SEBASTIAN ROZADILLA; ALEXIS M. ARANCIAGA ROLANDO; MOTTA J. MATIAS,; FERNANDO E. NOVAS; BRISSÓN EGLI F.; FERNANDO E. NOVAS

Buenos Aires

Jornada; XXX Jornadas Argentinas de Paleontología de Vertebrados; 2016

Comision organizadora de las XXX Jornadas Argentinas de Paleontología de Vertebrados

Antarctopelta oliveroi is the unique ankylosaur discovered on the Antarctic continent. It comes from the Santa Marta Formation (Santoniano-Campaniano), James Ross Island. Recently it was proposed as a chimaera, including elements belonging to marine reptiles, and thus, its nature as a valid species and genus was questioned, being considered as a nomen dubium. This hypothesis is supported on the idea that some of its autapomophic traits are more widely distributed among Ankylosauria than previously thought (anteroposteriorly short cervical centra, osteoderm morphotypes), whereas other features (anterior caudal vertebrae with slender transverse processes, notably dorsoventrally depressed posterior caudal centra, with slightly anteriorly inclined articular faces and well developed transverse processes) are present in bones considered as belonging to marine reptiles (i.e. mosasaurs and elasmosaurids). An overview of available material allows reconsidering some previous proposals. The caudal vertebrae do not belong to marine reptiles, but to ankylosaurs as originally interpreted. In fact, caudal elements show on its ventral surface a pair of longitudinal ossified tendons. This kind of tendons is totally absent in any known marine reptile. The unique combination of nodosaurid and ankylosaurid characters of Antarctopelta¸ together with a possible autapomorphic trait (distal caudal vertebrae, with well developed and anteroposteriorly expanded transverse processes) indicate that it may be considered as a valid ankylosaur taxon.