In the late Precambrian, 590 million years ago (mya), Antarctica was the central part of the super continent Gondwana, which remained intact for 400 million years (Ma). Fragmentation and the continental drift took Antarctica to its present position about 65 mya, at the beginning of the Cenozoic. The final separation from South America occurred at 22–25 mya, in the Oligocene-Miocene transition. The opening of the Drake passage produced the Circum- Antarctic Current and the development of the Antarctic Polar Front (or Antarctic Convergence). With reduction of heat exchange from northern latitudes, cooling of the environment proceeded to the present extreme conditions. The Antarctic ocean became gradually colder and seasonally ice covered. Although sea ice may have already been present at the end of the Eocene (40 mya), extensive ice sheets have probably formed only after the middle Miocene (14 mya) every 1–3 Ma. The latest ice-sheet expansion, with progressive cooling leading to the current climatic conditions, began 2.5 mya in the Pliocene. Antarctica is now a continent, almost fully coated with an ice sheet with average thickness of about 2000 m. It had enjoyed a much warmer climate than that of the dry, bitterly cold desert of the current times. Such variations produced many diversified forms of terrestrial and aquatic life (Eastman, 1991,1993).

The Antarctic fish fauna

For the study of temperature adaptations, Antarctica is a unique natural laboratory. Although in this environment the absence of antifreeze protection (DeVries, 1983) would cause rapid freezing of fish from temperate waters, the oxygen-rich Antarctic waters support a wealth of marine life.