Geochronology, taxonomy and morphology of select fossils of the Buchan Caves, south-eastern Australia

Abstract

The Buchan Caves, in the northeast of Victoria, contain a diverse and fascinating palaeofauna, reflecting a wide range of environmental conditions from the Pleistocene through to the present. Prominent within the assemblage is the Pleistocene-aged megafauna, represented at Buchan by Thylacoleo carnifex, Simosthenurus occidenta/is, 'Procoptodon' gilli, Zygomaturus trilobus, Diprotodon optatum, Protemnodon anak, Protemnodon sp., Sthenurus sp., Palorchestes azael and Palorchestes parvus. The objective of this thesis was to investigate the antiquity, morphology and myology of a newly discovered cranium of Palorchestes azael. Using Uranium-Thorium dating technique on calcite encrusting the fossil, a new date of 275 ± 0.03 Ka was determined, which allows correlation of this fossil locale with other fossiliferous cave deposits throughout Australia. Examination of comparative myology and osteology of vestibular-proboscis-bearing placental mammals, including Tapirus terrestris, Elephas maximus, Saiga tatarica andAlces alces, it is suggested that unlike older species within the genus, such as P painei, P azael did not possess a proboscis. Distinct differences in cranial morphology (such as the unusual positioning of the jugal, nasals and zygomatic arch, as well as foreshortening of the antero-dorsal surface of the cranium) indicates that P azael differs from all other species observed in this investigation. The differences observed in the masticatory musculature proposed a change in dietary behaviour from older species of Palorchestes. The large sinus cavities observed throughout the cranium of P azael are structurally analogous to those of Diprotodon optatum, a contemporary of P azael, and may represent a functional multi-derived feature, possibly evolved to reduce skull weight and increase surface area for the insertion of masticatory musculature.