The whales and dolphins of Tasmania: Part 1.--external characters and habits

Abstract

Whales are mammals which have become entirely aquatic, though there is every reason to believe that they have been derived from land mammals. As in the case of the specialized ichthyosaurian reptiles, the aquatic environment has imposed upon whales a fish-like form; the head passes imperceptibly into the trunk without a constricted neck; the anterior limbs or flippers have lost all externa1 semblance to the typical marnmalian fore-limb; and the hind limbs have disappeared, though internal skeletal vestiges still persist. A dorsal fin is generally present, but does not contain skeletal supports as in the ease of fishes. The well-developed caudal fin has no skeleton, and differs from the vertical tail of fishes in being prolonged laterally into fleshy horizontal expansions, the flukes. The nostrils (blowhole, single or double) are situated high upon the vertex of the head. The eyes are small, the external part of the ear is almost non-existent and has no pinna. Teeth are generally present at some stage in the life history, but in whalebone whales the teeth disappear before the end of foetal life. The blubber, which is characteristic of whales, is a thick subcutaneous tissue containing fat, and is impregnated with oil. The hairy covering, which is present in all mammals, is reduced to a few isolated hairs in the region of the mouth, and the body is naked and shiny. This group includes the largest animals which have ever lived.