Southern Ocean Southern Hemisphere, with the greatest concentration located on and around Antarctica. Four of the 18 penguin species live and breed on the mainland and its close offshore islands. Another four species live on the subantarctic islands. Emperor penguins have four overlapping layers of feathers, keeping them warm. They are the only Antarctic animal to breed during the winter. There are relatively few fish species in few families in the Southern Ocean. The most species-rich family are the snailfish (Liparidae), followed by the cod icefish (Nototheniidae) and eelpout (Zoarcidae). Together the snailfish, eelpouts and notothenioids (which includes cod icefish and several
Evolution of birds evolved into some basic lineages by the end of the Cretaceous (see "Vegavis"). The Neornithes are split into the paleognaths and neognaths. The paleognaths include the tinamous (found only in Central and South America) and the ratites, which nowadays are found almost exclusively on the Southern Hemisphere. The ratites are large flightless birds, and include ostriches, rheas, cassowaries, kiwis and emus. A few scientists propose that the ratites represent an artificial grouping of birds which have independently lost the ability to fly in a number of unrelated lineages. In any case, the available data regarding their evolution is still very