The extraordinary osteology and functional morphology of the limbs in Palorchestidae, a family of strange extinct marsupial giants

• Published in: PloS one Vol. 14; no. 9; p. e0221824
• Main Authors: Richards, Hazel L, Wells, Rod T, Evans, Alistair R, Fitzgerald, Erich M G, Adams, Justin W
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 13.09.2019; Public Library of Science (PLoS)
• Subjects: Analysis; Animal morphology; Animals; Australia; Biology and Life Sciences; Biomedical materials; Body mass; Body Size; Bone and Bones - anatomy & histology; Cranium; Diagnostic systems; Earth Sciences; Endangered & extinct species; Extinction, Biological; Extremities - anatomy & histology; Fossils - anatomy & histology; Functional morphology; Marsupialia - anatomy & histology; Marsupialia - classification; Marsupialia - physiology; Marsupials; Medicine and Health Sciences; Megafauna; Miocene; Morphology; Natural history; Oligocene; Physiological aspects; Pleistocene; Prehistoric animals; Skull; Skull - anatomy & histology; Species; Species Specificity; Australia
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0221824

The Palorchestidae are a family of marsupial megafauna occurring across the eastern Australian continent from the late Oligocene through to their extinction in the Late Pleistocene. The group is known for their odd 'tapir-like' crania and distinctive clawed forelimbs, but their appendicular anatomy has never been formally described. We provide the first descriptions of the appendicular skeleton and body mass estimates for three palorchestid species, presenting newly-identified, and in some cases associated, material of mid-Miocene Propalorchestes, Plio-Pleistocene Palorchestes parvus and Pleistocene Palorchestes azael alongside detailed comparisons with extant and fossil vombatiform marsupials. We propose postcranial diagnostic characters at the family, genus and species level. Specialisation in the palorchestid appendicular skeleton evidently occurred much later than in the cranium and instead correlates with increasing body size within the lineage. We conclude that palorchestid forelimbs were highly specialised for the manipulation of their environment in the acquisition of browse, and that they may have adopted bipedal postures to feed. Our results indicate palorchestids were bigger than previously thought, with the largest species likely weighing over 1000 kg. Additionally, we show that P. azael exhibits some of the most unusual forelimb morphology of any mammal, with a uniquely fixed humeroulnar joint unlike any of their marsupial kin, living or extinct.