Paleobiological inferences for the Antarctic dinosaur Antarctopelta oliveroi (Ornithischia: Ankylosauria) based on bone histology of the holotype

Abstract

A detailed histological study of Antarctopelta oliveroi, from the Upper Cretaceous of Antarctica, is performed in order to increase our knowledge of the ankylosaur bone histology and its taxonomical and paleobiological implications. The main goals of this contribution are: to infer the ontogenetic stage of the holotype of Antarctopelta oliveroi (MLP 86-X-28-1); to evaluate the degree of interelemental histological variation; to compare its histology with that of other ankylosaurs; to provide information about the phylogenetic affinities of Antarctopelta regarding dermal armor histology; and to evaluate the influence of a high latitude, strongly seasonal ecosystem on the growth of Antarctopelta. The sample includes several postcranial elements from the holotype (e.g. osteoderms, appendicular bones, dorsal ribs, ossified tendons). Bone histology reveals that the specimen was sexually mature at its time of death. Although a distinct Outer Circumferential Layer is not evident in all the sampled elements, the bone microstructure suggests quite slow appositional growth (i.e. most of the growth had already occurred) at the time of death. Primary cortical bone of the sampled elements, mostly composed of fibrolamellar bone tissue interrupted by growth marks, reveals a cyclical growth strategy as reported for other ankylosaurs and non-avian dinosaurs. The bone histology of Antarctopelta indicates that, as with other Southern Hemisphere polar dinosaurs, there are no apparent differences in growth strategy compared with its low latitude relatives. Therefore, no evident physiological modifications appears to be linked with the distribution of ankylosaurs and other non-avian dinosaurs at higher latitudes (>60° S).