there is evidence that this may have occurred about The subfamily of fishes Trematominae is endemic to 12-14 million years ago (MYA) (Eastman, 1993; the subzero waters of Antarctica and is part of the Bargelloni et al., 1994).
larger notothenioid radiation. Partial mitochondrial
There may have been a suite of factors which allowed sequences from the 12S and 16S ribosomal RNA (rRNA) the notothenioids, in particular, to evolve to such domigenes and a phylogeny for 10 trematomid species are nance in the Southern Oceans. Several authors have presented. As has been previously suggested, two taxa, suggested that speciation within the group could have Trematomus scotti and T. newnesi, do not appear to be been the result of large-scale disruptions in the Antarcpart of the main trematomid radiation. The genus Patic ecosystem during the Miocene (Clarke, 1983). The gothenia is nested within the genus Trematomus and isostatic pressure from the accumulation of ice during has evolved a unique cyropelagic existence, an associthe early Miocene (25-15 MYA) left the continental ation with pack ice. Using a mitochondrial rRNA moshelf unusually small, deep, and lacking extensive tolecular clock rate of 0.14% transversion changes per pography (Andersen, 1991). It is likely that the presmillion years, the average age of the trematomids is esence of ice, which destroyed high coastal habitats and timated at 3.4 million years (MY). If the age of the trecaused the depression of the continental shelf, resulted matomids is approximately 3.4 MY, this group could in the extinction of many other species. In addition, behave speciated during a period of deglaciation in Antcause the ice is anchored to the continent, riverine, esarctica 2.5-4.8 million years ago. This era was marked tuarine, and intertidal zones were completely lost. by significant changes on the Antarctic shores, such as
Hence, any species that did not live in the deeper wathe opening of fjords, which might have provided a ters may not have survived these periods of extensive stimulus for speciation.