Reappraisal of an ankylosaurian dinosaur from the Upper Cretaceous of James Ross Island (Antarctica)

The holotype of the upper Campanian ankylosaur Antarctopelta oliveroi n. gen., n. sp., from James Ross Island, Antarctica, is described. Diagnostic characters include short cervicals (centrum length about 70% of the centrum height), distal caudal vertebrae with transverse processes well developed (centrum width including the transverse processes exceeds 30% of the posterior articulation width) and dorsoventrally depressed, and the presence of smooth, sub-circular osteoderms, surrounded by a mosaic of smaller polygonal osteoderms with a rugose surface texture and tiny, button-like ossicles. While a number of features, such as relatively large teeth with respect to the mandible and the presence of an asymmetrical cingulum, suggest an affinity with the Nodosauridae, others such as the dorsoventrally depressed morphology of the distal caudal vertebrae and, especially, the presence of ossified tendons on their ventral side, characterize the Ankylosauridae. This uncertainty impedes evaluation of the paleobiogeographical significance of this new species of dinosaur.