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Department of Geology, University of Otago, P.O. Box 56, Dunedin, New Zealand
Austral marine mammals evolved in a Southern Ocean influenced by changing post-Gondwana geography and consequent new water-masses, progressive cooling, increased thermal gradients and physical and biological seasonality. The biology of extant species and temperate-to high-latitude fossils suggests, but does not confirm, that such factors have governed evolution, and that details of marine mammal evolution therefore differed from those of the north. Cladistic analyses may eventually allow better interpretation of the record.
Cetacea were present in high southern latitudes by the late Eocene. Mysticetes appeared in the south, where they may have originated, about the early Oligocene. They were diverse by the late Oligocene. Early records of Odontoceti are more ambiguous, but they were diverse by the latest Oligocene, when some taxa had circum-Antarctic distributions. The Neogene records of Austral Odontoceti and Mysticeti broadly complement the taxonomic and ecological diversification seen in the north. Amongst largely southern seals, lobodontine Phocidae radiated in the south about the late Miocene, and perhaps ecologically excluded the later arctocephaline Otariidae from high-latitude pagophilic lifestyles. There are no reports of the important northern groups Odobenidae, Sirenia or Desmostylia. Overall, southern marine mammal faunas were ecologically and/or taxonomically similar to extant faunas by the later Miocene to Pliocene.
