Evolution of the Antarctic fish fauna with emphasis on the Recent notothenioids

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Abstract
The composition of the Antarctic fish fauna has undergone remarkable changes through time. Fossil fishes are known from Devonian, Jurassic, Cretaceous and early Tertiary deposits of the region. The Recent fauna does not appear to be derived from any part of any of the known fossil faunas. The Devonian fish fauna includes agnathans, placoderms, acanthodians, chondrichthyans and osteichthyans all belonging to families now extinct. The Jurassic fauna is known by only one species, a neopterygian of the now extinct family Archaeomaenidae. Both the Palaeozoic and early Mesozoic fish faunas known from Antarctica indicate Australian biogeographic affinities based on other (i.e., non-Antarctic) known Palaeozoic and Mesozoic fish faunas. Late Cretaceous and early Tertiary species from the Antarctic region (Seymour Island) belong largely to families of fishes that today live in other regions of the world, but are extinct in the Antarctic region. The Recent (extant) fish fauna is drastically different from any of the fossil faunas and is dominated by perciforms of the suborder Notothenioidei. To date the fossil record has provided no fossils identifiable as notothenioids, or even species closely related to the group. It is unlikely that low water temperatures were directly respnsible for the local extinction of the Tertiary Seymour Island ichthyofauna or for the lack of diversity in the Recent fauna. The decline of suitable substrate and trophic factors may have been more important in changing the composition of the fish fauna. There is considerable morphological, physiological and ecological diversification within the Notothenioidei. Although the emergence of this group was probably not a direct response to cooling, the subsequent radiation of notothenioids was associated with a variety of specializations related to low water temperature.