In Ogmorhinus all the teeth of the cheek-series have three distinct pointed cusps, deeply separated from each other, of which the middle or principal cusp is largest and slightly recurved; the other two are nearly equal in size, and have their tips directed towards the middle one. Skull much elongated. One species, O. leptonyx, the sea-leopard, widely distributed in the Antarctic and southern temperate seas. In Lobodon the molars have compressed elongated crowns, with a principal recurved cusp, rounded and somewhat bulbous at the apex, and one anterior, and one, two or three posterior distinct accessory cusps. One species, L. carcinophagus, the crab-eating seal. In the third genus, Leptonychotes, represented by L. weddelli, the molars are small, with simple, subcompressed, conical crowns, and a broad cingulum, but no distinct accessory cusps. Finally in the white seal (Ommatophoca rossi) all the teeth are very small, those of the cheek-series with pointed, recurved crowns, and small posterior and still less developed anterior accessory cusps. Orbits very large. Nails rudimentary on front and absent on hind-feet. The skull bears a considerable resemblance to that of the next subfamily.
The presence of two pairs of upper and one pair of lower incisors is characteristic of the members of the subfamily Cystophorinae, in which the teeth of the cheek-series are generally one-rooted. The nose of the males has an appendage capable of being inflated. First and fifth toes of hind-feet greatly exceeding the others in length, with prolonged cutaneous lobes, and rudimentary or no nails. In the typical genus Cystophora the dentition is i. 2⁄1, c. 1⁄1, p. 4⁄4, m. 1⁄1; total 30; the last molar having generally two distinct roots. Beneath the skin over the face of the male, and connected with the nostrils, is a sac capable of inflation, when it forms a kind of hood covering the upper part of the head. Nails present, though small on the hind-feet. Represented by C. cristata, the hooded or bladder-nosed seal of the Polar Seas. In Macrorhinus the dentition is numerically the same as in the last, but the molars are of simpler character and all one-rooted. All the teeth, except the canines, very small relatively to the size of the animal. Hind-feet without nails. Vertebrae: C. 7, D. 15, L. 5, S. 4, Ca. 11. Nose of adult male produced into a short tubular proboscis, ordinarily flaccid, but capable of dilatation and elongation under excitement. One species, M. leoninus, the elephant-seal, or “sea elephant” of the whalers, the largest of the whole family, attaining the length of nearly 20 ft. Formerly abundant in the Antarctic Seas, and also found on the coast of California.
The next family is that of the walruses, or Odobaenidae, the single generic representative of which is in some respects intermediate between the Phocidae and Otariidae, but has a completely aberrant dentition. Walruses have no external ears, as Walrus in the Phocidae; but when on land the hind-feet are turned forwards and used in progression, though less completely than in the Otariidae. The upper canines are developed into immense tusks, which descend a long distance below the lower jaw. All the other teeth, including the lower canines, are much alike, small, simple and one-rooted, the molars with flat crowns. The skull is without post-orbital process, but has an alisphenoid canal. In the young the dentition is i. 3⁄3, c. 1⁄1, p. and m. 5⁄4, but many of these teeth are, however, lost early or remain through life in a rudimentary state, concealed by the gums. The teeth which are usually developed functionally are i. 1⁄0, c. 1⁄1, p. 3⁄3, m. 0⁄0; total 18. Vertebrae: C. 7, D. 14, L. 6, S. 4, Ca. 9. Head round. Eyes rather small. Muzzle short and broad, with a group of long, very stiff, bristly whiskers on each side. The remainder of the hair-covering very short and closely pressed. Tail rudimentary. Fore-feet with subequal toes, carrying five minute flattened nails. Hind-feet with subequal toes, the fifth slightly the largest, with cutaneous lobes projecting beyond the ends as in Otaria; first and fifth with minute flattened nails; second, third and fourth with large, elongated, subcompressed pointed nails. The two species are Odobaenus rosmarus, of the Atlantic, and the closely allied O. obesus, of the Pacific. (See [Walrus].)
| Fig. 7.—Skull and dentition of Australian Sea-Bear (Otaria forsteri). |
The third and last family of the Pinnipedia, and thus of existing Carnivora, is the Otariidae, which includes the eared seals, or sea-lions and sea-bears. In all these animals, when on land, the hind-feet are turned forwards under the body, and Sea-lions aid in supporting and moving the trunk as in ordinary quadrupeds. There are small external ears. Testes suspended in a distinct external scrotum. Skull with post-orbital processes and alisphenoid canal. Soles of feet naked. By many naturalists these seals are arranged in a number of generic groups, but as the differences between them are not very great, they may all be included in the typical genus Otaria. The dental formula is i. 3⁄2, c. 1⁄1, p. 4⁄4, m. 1 or 2⁄1; total 34 or 36. The first and second upper incisors are small, with the summits of their crowns divided by deep transverse grooves into an anterior and a posterior cusp of nearly equal height; the third large and canine-like. Canines large, conical, pointed, recurved. Molars and premolars usually 5⁄5, of which the second, third and fourth are preceded by milk-teeth shed a few days after birth; sometimes (as in fig. 7) a sixth upper molar (occasionally developed on one side and not the other); all with similar characters, generally single-rooted; crown moderate, compressed, pointed, with a single principal cusp, and sometimes a cingulum, and more or less developed anterior and posterior accessory cusps. Vertebrae: C. 7, D. 15, L. 5, S. 4, Ca. 9-10. Head rounded. Eyes large; ears small, narrow and pointed. Neck long. Skin of the feet extended far beyond the nails and ends of the digits, with a deeply-lobed margin. The nails small and often quite rudimentary, especially those of the first and fifth toes of both feet; the best-developed and most constant being the three middle claws of the hind-foot, which are elongated, compressed and curved.
Sea-bears and sea-lions are widely distributed, especially in the temperate regions of both hemispheres, though absent from the coasts of the North Atlantic. They spend more of their time on shore, and range inland to greater distances than the true seals, especially at the breeding-time, though they are obliged to return to the water to seek their food. They are gregarious and polygamous, and the males usually much larger than the females. Some possess, in addition to the stiff, close, hairy covering common to the group, a fine, dense, woolly under-fur. The skins of these, when dressed and deprived of the longer harsh outer hairs, constitute the “sealskin” of commerce. The species include O. stelleri, the northern sea-lion, the largest of the genus, from the North Pacific, about 10 ft. in length; O. jubata, the southern sea-lion, from the Falkland Islands and Patagonia; O. californiana, from California; O. ursina, the sea-bear or fur-seal of the North Pacific, the skins of which are imported in immense numbers from the Pribiloff Islands; O. antarctica or pusilla, from the Cape of Good Hope; and O. forsteri, from Australia and various islands in the southern hemisphere. (See [Seal-Fisheries].)
Little is known as to the past history of the sea-lions and sea-bears, but a skull has been obtained from the Miocene strata of Oregon, which Mr F.W. True states to be considerably larger than any existing sea-lion skull; its basal length when entire being probably about 20 in. The name Pontoleon magnus has been proposed for this fossil sea-lion, as the character of the skull and teeth do not agree precisely with those of any living member of the group. If, however, all the modern eared seals are included in the genus Otaria, there is apparently no reason to exclude the fossil species.
Extinct Carnivora
Modern Carnivora are undoubtedly the descendants of the Creodonta (q.v.), an extinct early Tertiary suborder. It has been observed that as the Miocene is approached, some of these Carnivora Creodonta, or Primitiva, begin to assume more and more of the characteristics of the Carnivora Vera, till at last it is difficult to determine where the one group ends and the other commences. The creodont genera Stypolophus and Proviverra show some of these modern characters; but it is not till we reach the European Oligocene genus Amphictis, with the dental formula i. 3⁄3, c. 1⁄2, p. 4⁄4, m. 2⁄2, that we meet a type in which the fourth upper premolar and the first lower molar assume the truly sectorial character of the Carnivora Vera, while the teeth behind them are proportionally reduced in size. From the Amphictidae are probably descended the Viverridae, the connecting genus being the African Nandinia, which, as already mentioned, retains the imperfectly ossified bulla of the ancestral forms. In another direction, Amphictis, through the Old World Lower Pliocene genus Ictitherium, has given rise to the Hyaenidae. The Felidae have apparently an ancestral type in the creodont Palaeonictis, which has been regarded as the direct ancestor of the sabre-toothed cats, or Machaerodontinae (see [Machaerodus]); but it is possible that Palaeonictis may be off the direct line, and that the Felidae are sprung from Amphictis. Be this as it may, from another group of creodonts, represented by Vulpavus (Miacis), Viverravus (Didymictis), and Uintacyon, is probably derived the Oligocene Cynodictis, with a dental formula like that of Canis or Cyon, a perforation to the humerus, and an apparently undivided auditory bulla; and from Cynodictis the transition is easy to the Canidae. It should be mentioned, however, that there is a group of North American Oligocene dog-like animals, such as Daphaenus, Protemnocyon, and Temnocyon, which agree with Cyon in the shortness of the jaws, and with that genus and Speothos in the cutting-heel of the lower sectorial. Possibly these genera may be nearly related to Cyon. Other dog-like North American types are Oligohinis, Enhydrocyon and Hyaenocyon.
By means of the Amphicyonidae, as represented by the Middle Tertiary genera Proamphicyon, Pseudamphicyon, and Amphicyon, in which there were three upper molars, we have a transition from the Cynodictis-type to the bear-group; one of the later intermediate forms being the Lower Pliocene Old World Hyaenarctus, in which the two upper molars are squared and foreshadow those of Ursus itself. In some unknown manner Hyaenarctus appears to be related to Aeluropus. An allied type is found in Arctotherium of the South American Pleistocene.