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Division of Continental Geology, Bureau of Mineral Resources, PO Box 378, Canberra, ACT, 2601, Australia
The Aztec fauna is one of the most diverse fossil vertebrate faunas from Antarctica, with over 30 taxa belonging to the four major groups of jawed fishes (acanthodians, placoderms, osteichthyans, chondrichthyans), and one group of agnathans (thelodontids). Biogeographically the strongest affinity is with eastern Australia, as part of the East Gondwana Province. Biostratigraphically the Aztec succession includes probably the youngest known non-marine thelodont agnathans at the base, and the oldest known phyllolepids at the top. This transition, and an association of species of Turinia and Bothriolepis, is not seen in any other sequence. Most or all of the Aztec sequence is regarded as Givetian (late Middle Devonian) in age. The Aztec fauna contains older and/or more primitive representatives of several groups typical of younger (late Palaeozoic) strata in Euramerica, suggesting a biotic dispersal episode between Gondwana and Euramerica in the Late Devonian. Centres of origin and dispersal hypotheses in Palaeozoic biogeography can be related to disappearance of faunal barriers as manifested in different stratigraphic ranges in different areas. The change for Devonian vertebrates from the endemic patterns seen in the Early Devonian to the close similarity of Famennian faunas between East Gondwana and Euramerica suggests disappearance of a major faunal barrier in the Late Devonian, presumably the ocean between Gondwana and Euramerica.
