Abstract
This thesis describes Australodelphis mirus and Australodelphis new species (Odontoceti: Delphinidae, new genus, new species), two species of dolphin from the Early Pliocene glaciomarine S0rsdal formation, Marine Plain in the Vestfold Hills, East Antarctica. These two extinct species are Early Pliocene in age and are known from skulls, tympanoperiotics and postcranial elements from seven individuals. The fossils represent the only reported higher vertebrate fossils from the Antarctic Late Oligocene to Pleistocene interval. Both dolphin species have bone contact relationships similar to those of extant delphinids; however, both species have a remarkably convergent cranial topography with extant toothless beaked whales in the family Ziphiidae (Cetacea: Odontoceti). In particular, Australodelphis mirus appears dramatically convergent with beaked whales in the genus Mesoplodon (Odontoceti: Ziphiidae). These similarities suggest that Australodelphis mirus perhaps had ziphiid-like habits (echolocating, suction-feeding, and possibly teuthophagy). Australodelphis mirus and Australodelphis new species appear to be related to extant longirostral delphinids (Delphinidae: Delphininae), although both species appear too derived to be ancestral to any living delphinids.
Other fragmentary specimens from Marine Plain represent a species of small right whale (Mysticeti: Balaenidae: genus and species uncertain).
These cetacean fossils from Marine Plain are unique in that small dolphins, small ziphiids and small right whales do not appear to be ecologically important in the modern Antarctic waters. Elsewhere, Early Pliocene and Late Miocene cetacean assemblages are rather different from Late Pliocene - Recent assemblages, pointing to as-yet poorly understood changes in cetacean ecology in about the middle of the Pliocene.