Cetacea

Cetacea, an order of aquatic mammals, widely distributed in all seas, with some forms that live in, and others that from time to time ascend large rivers. The order dates from Eocene times, and fossil species occur down to post-Pliocene times. Professor Flower thinks that the Cetacea are closely related to the Ungulates, and that their origin was fluviatile, while Dr. Murie is of opinion that the order "taken as a whole does not show substantial links of affinity with the other marine mammalia or with the land mammalian groups." The general conformation is fish-like; the tail is developed into a powerful swimming organ by its horizontal expansion into "flukes." The head is very large, and produced into a kind of snout; the eye is small, and the external ear wanting. The skin is smooth, and immediately, overlies a thick layer of fat - the blubber; there is generally a triangular dorsal fin; the fore limbs are reduced to paddles, and the hind limbs are absent or only indicated internally; the pelvis also is rudimentary. The nostrils, blowholes, or spiracles are generally on the top of the head, and the so-called "blowing" is only the ordinary breathing of these animals, which do not expel from these blowholes water taken in at the mouth. In size the Cetacea differ greatly - from four feet to sixty feet or more in length. They are generally inoffensive, and for the most part feed on small molluscs and crustacea, the grampus (q.v.) alone preying on warm-blooded animals, e.g. small dolphins or porpoises.