The essential characteristic of the Carnivores is the dentition, which is adapted to seizing, holding, biting, and cutting. The canines, rarely prominent in other groups, here become of prime importance—a dagger and hook in one—a tearing instrument. Naturally this tooth is most developed in the dogs and the bears, which have little other means of seizing and holding an animal, whereas the cat has efficient aid in its claws. The cheek teeth in this order are (typically) not flat "grinders" but angular and knife-edged, especially the foremost molars that shut past one another like scissor blades; and it is evident that such teeth are necessary to animals that must cut their food into pieces small enough to swallow, and are not concerned about chewing it. The order contains two distinct divisions, namely:
Marine Carnivores—Seals, sea lions, walruses.
Land Carnivores—Cats, dogs, weasels, bears, etc.
The marine carnivores (suborder Pinnipedia, "fin-footed") have their whole organization adapted to an aquatic life, and appear to have acquired it almost from the beginning of the diverse specialization that sprang from the generalized creodonts, for nothing is known of their ancestry that connects them with the known lineage of their kin on land. The body approaches a fishlike form, and the four limbs are turned into more or less perfect paddles, or "flippers." The teeth are of the carnivorous type; the eyes are always large and prominent; and external ears are lacking except in one family.
The least modified of the three families of marine carnivora is that of the eared seals—the sea lions and fur seals of the North Pacific ocean, and southward to Cape Horn. They have kept much independence of action in the hind limbs, and are able to climb readily about the rocks of the islands and shores to which they resort in midsummer for the birth of the young. They have an obvious neck, small external ears, nostrils at the tip of the snout, and in general more characteristics like those of land carnivores, especially the bears, than have any other pinnipeds. They live wholly on fish. Several species termed "sea lions" were formerly numerous from Oregon southward to Patagonia, and on certain South Sea islands, but they have been all but exterminated except in California. These southern species, dwelling in warmer latitudes, are known as "hair" seals, because their coat lacks the warm undercoat of the northern species (Otaria ursina) which is the "fur" seal of commerce, and which would long ago have disappeared had it not been placed under international protection in its breeding places on islands in Bering Sea. Thither, as summer opens the ice, gather the herds that have been wandering in the ocean during the winter. The females are much the more numerous of the two sexes, and having spread all over the islands, formerly in hundreds of thousands, are collected into "harems." The "bulls" are three times the size of any of the females, and there are incessant combats between rival bulls. The young born here are strong enough to swim away with their mothers in the early autumn.
Similar in general organization, and in the freedom and usefulness of the hinder limbs for creeping on land or ice, are the walruses (Trichechidæ), of which there are two arctic species, one in the North Atlantic, and one in the seas of Alaska and Kamchatka. In old times they came as far south in winter as Nova Scotia and the coasts of Britain. A full-grown male walrus is a very bulky animal, ten to twelve feet long, and his skin is covered with a short coat of hair that in old age almost disappears, while his bulldoglike muzzle bristles with quill-like whiskers. The especial feature of the walrus, however, is the pair of great ivory tusks, often two feet or more long, which are the canines of the upper jaw. They are the tools with which the animal digs from the mud of the bottom the clams and other shellfish on which it feeds, and are formidable weapons enabling it to protect itself and its family and mates, for which the walrus shows remarkable affection and loyalty, from the attacks of the polar bear, the only enemy besides man that it has to fear.
The true seals (Phocidæ) have become still further specialized toward a completely aquatic life. Their hind limbs are extended straight behind the body, and take no part in progression, the fore flippers alone enabling them to swim and dive with ease and speed. Their strong, clawlike nails enable them to climb onto ice floes or the shore, to which they resort for rest and sunshine and to bear their young. These are usually only one, or at most two, at a birth, and in some species they have to be carefully taught how to swim, fearing the water. All of the many kinds of seals of this family are confined to the northern hemisphere, and mostly to the arctic region; but the great sea elephant, now almost extinct, lived in the antarctic, with one colony on the coast of southern California. Most seals are gregarious, and some congregate in immense herds on ice floes far from land, but the majority of species stay near shore. Seals feed chiefly on fish, of which they consume enormous quantities; some, however, subsist largely on crustaceans, especially prawns that swarm in the northern seas; also on mollusks, echinoderms, and even occasionally on sea birds.
We are now ready to turn to the land carnivores, which, by the larger opportunity, better food, and varied conditions the land affords, have advanced far beyond their marine cousins. In these more favorable circumstances, and by their struggle for a living against the powers of defense or escape of their intended prey, and the competition of one another, they have become widely diversified in organization and habits, and in some of their representatives have developed the highest intellectual and physical ability in the animal kingdom.