CARNIVORE

a member of the mammalian order Carnivora, literally meat eaters. The order Carnivora is composed of 10 families of primarily predatory mammals: the dogs, foxes, wolves, and jackals (Canidae); bears (Ursidae); raccoons and pandas (Procyonidae); weasels, skunks, otters, and badgers (Mustelidae); genets, civets, and mongooses (Viverridae); hyenas (Hyaenidae); cats (Felidae); sea lions, or eared seals (Otariidae); earless seals (Phocidae); and the walrus (Odobenidae). Although the term carnivore can be applied broadly to any meat-eating animal, including mammals in other orders such as the otter shrews (Insectivora) and the Tasmanian devil (Marsupialia), mammalogists generally use the term in this more restricted sense. Most members of the order are in fact meat eaters, although some ursids, procyonids, and canids rely heavily on vegetation, and the giant panda (Ailuropoda melanoleuca) lives almost entirely on bamboo shoots. Marine carnivores (the three families of pinnipeds, or seal-like forms) are found in all oceanic waters and along the coasts of all the continents. Terrestrial carnivores are native to all continents but Antarctica and Australia, although the dingo (Canis dingo) was introduced to the latter during the early Aboriginal invasion. The smallest carnivore, the least weasel (Mustela nivalis), weighs only 30 to 70 grams (1 to 2.5 ounces), while the largest terrestrial species, the Alaskan brown bear (Ursus arctos), can reach 780 kilograms (1,700 pounds). The largest member of the order is the elephant seal (Mirounga leonina) at 3,600 kilograms (4 tons). Carnivores exhibit a wide variety of forms. The pinnipeds have evolved paddle-like extremities; the limbs are enclosed within the streamlined torso down to at least the elbows or knees, and the remaining portion of the limb is flattened as a flipper that provides efficient aquatic propulsion. Among the terrestrial carnivores, body forms may be adapted for running (many canids), stalking (felids), climbing (many viverrids), and swimming (otters). Most carnivores have a fairly complex dentition; incisors, canines, premolars, and molars occur in that order. In those members of the order that live mainly on meat, some of the side teeth have evolved into the scissorlike carnassials, or shearing teeth. The teeth behind the carnassials are usually absent. In carnivores the incisor teeth usually function for nipping, and the large sharp canines are used to grab and hold the prey. The more omnivorous ursids and procyonids lack carnassials and have retained more of their molar teeth for grinding their food. Pinnipeds show less variety in tooth structure than other carnivores, their premolars and molars all being essentially conical structures that are efficient for grabbing and holding fish. The lower jaw of carnivores is hinged in such a way that it can move only vertically, but it can exert great power. Collarbones are absent or reduced, which allows great flexibility in the shoulder area. The brains of carnivores are relatively large for their body weights and, characteristic of the more intelligent animals, are highly convoluted. The stomach is simple and the intestine short, both typical features of carnivorous animals, as animal tissue is easier to digest than vegetable tissue. The earliest carnivores, the Miacidae, appeared during Paleocene times (about 60,000,000 years ago). The group probably evolved from an insectivorous ancestor. By late Eocene times two distinct lines were apparent within the Carnivora; the Feloidea (which led to the cats, viverrids, and hyenas) and the Canoidea (dogs, mustelids, bears, and procyonids). Among the feloids, the viverrids are so similar to the ancestral miacids that some mammalogists place both in the family Viverridae. The two main characteristics distinguishing these lines are the presence of retractile or semi-retractile claws in most feloids and a difference in the structure of the tympanic bulla, which in feloids is composed of an external tympanic bone and an internal endotympanic bone and in canoids is composed of only the tympanic bone. The populations of various carnivores are limited by the availability of prey. Most carnivores space themselves out by establishing and maintaining territories. The size of these territories depends on the size of the predator and the carrying capacity of the prey population; a mountain lion (Felis concolor) needs a large territory to support the deer herds it preys on, while a bobcat (F. rufus) can usually support itself on the rabbit population of a much smaller area. Hunting patterns differ throughout the Carnivora. Most canids have great endurance and are built to run down their prey. The cats, on the other hand, tire quickly and are adapted to stalking and leaping upon their prey. When their hooked claws are extended the foot also expands; this gives them a large surface with which to grasp and hold the prey. Although they are the largest land carnivores, the bears live mainly on insects, seeds, nuts, plant matter, and berries; some species also fish. Only the polar bear (Ursus maritimus) is mostly predatory; its Arctic environment has little vegetation, and this highly aquatic bear lives mainly on seals. The sea otter (Enhydra) is among the tool-using mammals. Its diet consists of abalone and other shellfish, which it opens by cracking them on a rock held on its chest as it floats on its back. Some carnivores are quite solitary (most of the cats, civets, bears, and weasels); others live and hunt in pairs or with the young of the year (foxes and the kinkajou, Potos flavus). Some, including the wolves, Cape hunting dogs (Lycaon pictus), lions (Panthera leo), coatimundi (Nasua), and some mongooses, live and hunt in larger social groups. Pinnipeds live in huge rookeries during the breeding season; in many species the males establish breeding territories and maintain harems. Mating patterns vary from the temporary liaisons seen in the bears and most cats to the monogamous pairs found in many species of canids. Delayed implantation (in which the embryo floats freely in the womb for up to several months before embedding in the uterine wall and commencing development) is found in many mustelids and the bears. Litter size is generally between 3 and 6; bears usually have only 2 cubs, while the Asiatic polecat (Mustela eversmanni) may produce up to 18 young. Young carnivores are cared for by one or both parents, depending on the species, and in some, such as the Cape hunting dog, the entire pack feeds and guards the pups once they stop nursing. Young carnivores remain with the adults until they have learned basic hunting skills. Many carnivores will bring wounded game back to their young so they can practice catching and killing. Small carnivores, such as mustelids, may be mature and breeding at one year of age, but the larger ones, such as bears, do not mature until three or four. Male pinnipeds may be much older than that before they can compete with the dominant males for a chance to breed. any member of the order Carnivora, literally meat eaters. The order includes 10 families of living mammals: Canidae (dogs, wolves, jackals, and foxes), Ursidae (bears), Procyonidae (raccoons), Mustelidae (skunks, mink, weasels, badgers, and otters), Viverridae (civets and mongooses), Hyaenidae (hyenas), Felidae (cats), Otariidae (eared seals), Odobenidae (walrus), and Phocidae (earless seals). The term carnivore is frequently applied by mammalogists to members of this order and is employed in that sense in the present article. In a more general sense, a carnivore is any animal (or even, occasionally, a plant) that eats the flesh of other animals, as opposed to a herbivore, which eats plants. Although the Carnivora are basically meat eaters, a substantial number, especially among bears and procyonids, feed extensively on vegetable material. Additional reading For general information on the biology of the carnivores, see E.P. Walker et al., Mammals of the World, 3 vol. (1964), in which each genus is described and illustrated, along with a brief summation of its biology. The taxonomy of carnivores is discussed in G.G. Simpson, Principles of Classification and a Classification of Mammals, Bull. Am. Mus. Nat. Hist., vol. 85 (1945), a classic work on classification, followed by most recent mammalogists; and H.J. Stains, Carnivores and Pinnipeds, in S. Anderson and J.K. Jones, Jr. (eds.), Recent Mammals of the World: A Synopsis of Families (1967). F.E. Beddard, Mammalia (1902, reprinted 1958), is a definitive early work on mammalian anatomy. The paleontology of the Carnivora is summarized in two works by A.S. Romer: Vertebrate Paleontology, 3rd ed. (1966), fundamental to an understanding of fossil forms, and Notes and Comments on Vertebrate Paleontology (1968), containing additional information not found in the general text. Books devoted to particular subgroups of the carnivores include A. Denis, Cats of the World (1964), an excellent summary of the status of all members of the Felidae; C.J. Harris, Otters (1968), a fine summary of the status of the otters around the world; H.E. Hinton and A.M.S. Dunn, Mongooses: Their Natural History and Behaviour (1967), which contains much interesting information that is difficult to find elsewhere, except in scattered literature; R.J. Harrison et al. (eds.), The Behavior and Physiology of Pinnipeds (1968), an excellent summation of knowledge on these aquatic carnivores; and V.B. Scheffer, Seals, Sea Lions, and Walruses: A Review of the Pinnipedia (1958), a major work on the taxonomy of the Pinnipedia. Howard James Stains Evolution and paleontology Opinion is divided as to whether the order Carnivora arose from the ancient creodonts or had a separate and independent origin from the order Insectivora. Most paleontologists now favour the latter view. The Cretaceous insectivore Procerberus seems to be morphologically close to the most primitive carnivores (miacids), the creodonts, and the primitive hoofed mammals (ungulates). Procerberus was an unspecialized rat-sized predator. The order seems to be a separate and distinct line that includes the modern Fissipedia (terrestrial forms) as well as Pinnipedia (marine and aquatic forms), while also including the more ancient and extinct family Miacidae. Although not much is known about them, the miacids were probably arboreal forest dwellers of the tropics. Animals from this type of habitat are rarely preserved as fossils, which accounts for our incomplete knowledge of the group. These primitive carnivores may have resembled our modern weasels, with elongate bodies, short limbs, and long tails. Miacids possessed several creodont features, such as an unossified tympanic bulla (a large bubble of bone or cartilage surrounding the internal ear) and lack of fusion of the carpal (wrist) bones. Miacids differed from the creodonts in having a larger brain capacity, toe sections that were not grooved, and well-developed carnassial teeth. The carnassials, as in modern carnivores, involved the fourth upper premolar and first lower molar. In the late Eocene and early Oligocene these primitive miacids underwent an adaptive radiation; i.e., they produced diverse lines that seem to have been the beginnings of the present-day families of the Carnivora. The changes needed to convert a miacid into a modern terrestrial carnivore are minor: fusion of the separate bones of the carpus and ossification of the tympanic bulla. Carnivores that began to resemble the modern weasels, dogs, and civets were in evidence in the Oligocene, but these early carnivores were still quite similar to each other and had not differentiated to the extent of representing different families. Two major lines within the Carnivora were distinct by the late Eocene. One, the Feloidea (or Aeluroidea), today contains cats, viverrids, and hyenas; the other, the Arctoidea (or Canoidea), contains the mustelids, dogs, bears, and raccoons. Some fossils are intermediate between the two lines, but most show definite relationships to one or the other. Feloids had the tympanic bulla made up of an external (tympanic) and an internal (endotympanic) bone, each being a separate ossification. In many forms the claws were retractile. The transition between the miacids and viverrids (civets) was so gradual that some authorities have placed the miacids in the family Viverridae. Because of the similarities to the miacids, the viverrids are considered to form the basal stock of the feloid line. Hyenas appear to be a more recent line, having evolved from the viverrids in the early Miocene. Ictitherium, a mid-Miocene viverrid, had characteristics intermediate between the viverrids and hyenas, but apparently was more like the true hyenas. Other fossil viverrids also showed similarities to the hyenas. Although the cats seem to have evolved suddenly, the resemblance of certain catlike viverrids (such as the Oligocene Stenoplesictis and the modern Cryptoprocta of Madagascar) to the recognized felids is regarded by some authorities as indicating the close relationship of the felids to the viverrids. In the late Eocene and early Oligocene, the felids were quite distinct, with a number of highly specialized cats already present. Of particular interest are the sabre-toothed cats such as Hoplophoneus and the false sabre-tooth Dinictis, which had large upper canines fitting into a flange on the lower jaw. The Pleistocene Smilodon, a more recent genus, is probably the best-known sabre-toothed cat. The genus Felis dates back to the early Pliocene, by which time its members had features similar to those of the modern cat. In contrast to the feloids, the arctoids almost never had retractile claws; the tympanic bulla was made up of the tympanic bone alone; and there was a canal below the bulla, through which the carotid artery passed, supplying blood to the brain. Some of the earlier miacids are difficult to separate from the mustelids, which were distinct as early as the late Eocene. They probably were one of the first arctoid lines to differentiate. By the close of the Miocene, several general types of mustelids were evident: the weasels, badgers, skunks, and otters. Another ancient arctoid line included the dogs. Oligocene canids, represented by the genera Cynodictis and Hesperocyon, resembled elongate, short-legged weasels and civets. Both genera, although considered to be primitive dogs, were generalized enough to be ancestral to many carnivores. Genera that were more typically canid appeared in the early Oligocene. These were running animals, with four well-developed toes and reduced hindtoes (hallux and pollex), each ending in a blunt claw. More than 50 genera of doglike forms are known, but the main line of evolution seems to have passed through forms like Temnocyon (upper Oligocene) and Cynodesmus (lower Miocene) to the modern genera Canis (first seen in the lower Pliocene deposits), Vulpes (perhaps in the upper Miocene), and Urocyon (Pleistocene). Two lines of extinct canids are the hyena-like dogs and the bear dogs, neither of which has any relationship to the living hyenas or bears. Because of the close relationships of the bears, dogs, and raccoons, various taxonomists have disagreed on the placement of intermediate genera. For example, Dinocyon, Hemicyon, and Cephalogale were once considered to have been canids but are now placed with the bears and regarded as perhaps part of the ancestral lineage that diverged from the canid line in the late Oligocene or early Miocene. Phlaocyon and Aletocyon were once considered to be primitive procyonids because of their teeth, but the skull and ear structures are more reminiscent of the dogs. A recent form, the giant panda (Ailuropoda), considered by some to be a bear and by others to be a procyonid, probably diverged from primitive ursid stock when the ancestor of the bear and raccoon lines still had features common to both. Procyonids (raccoons) are poorly represented in the fossil record, perhaps because of their arboreal habits. They appear to have diverged from the canid line in the late Oligocene. The preponderance of carnivorous and carrion-eating fishes and mammals in the open sea, along with the buoyant characteristics of the bodies of the pinnipeds, results in the almost immediate destruction of any seal that dies. Thus, dead pinnipeds seldom settle intact and become buried (the first steps toward becoming a fossil) and are poorly represented in the fossil record. Relationships must instead be inferred through studies of recent forms. Although there is no fossil record of pinnipeds prior to the Miocene, it is probable that the ancestors of the pinnipeds evolved during the adaptive radiation of the miacids in the Eocene. There are two rather distinct evolutionary lines in the animals called pinnipeds. One includes the two rather closely related families Otariidae and Odobenidae. This line may have become distinct in the early Miocene or late Oligocene, evolving from a form closely related to the canid ancestor of the bears. The other line led to the modern phocids, which are quite different from the otaridodobenid group. Their affinity to any other group of the Carnivora has not been shown, although the mustelids have more frequently been suggested as related to the phocids than any other group. Semantor, an aquatic carnivore from the lower Pliocene, was once considered to belong to a separate pinniped family but is now considered a mustelid. The separation of the phocid and otaridodobenid lines must have occurred at an extremely early date, if the two lines ever had a common pinniped ancestor. Some paleontologists postulate a separation in the early Miocene or late Oligocene. Possibly the two lines never evolved from a single aquatic group but had separate origins within the miacids, sometime in the late or even mid-Eocene. Or perhaps the otarids stemmed from an ancestral ursid type in the early Oligocene. Such an early separation, or lack of any real ancestral association, could have produced the dissimilarity of the two types of pinnipeds, as well as the difficulty in associating the phocids with any other family of the Carnivora. Classification Distinguishing taxonomic features If one groups the seals with the terrestrial carnivores, the number of characteristics common to all members of the order Carnivora is small. The characteristics used to separate the Carnivora from other mammalian orders and to define the subdivisions of the Carnivora are primarily structural. Of great importance are certain features of the skull (the type of jaw articulation and the shape of the paroccipital process), of the feet (the number of toes, lack of opposability of the hindtoe, type of claws, and fusion of the scaphoid and lunar bones), and of the teeth (both the overall tooth pattern and the shape of the individual tooth). The dentition is especially important in determining the relationships of fossil forms. Also useful in the taxonomy of modern carnivores are the convolutions (irregular ridges) around the lateral or sylvian fissure of the brain, the relative weights of the adrenal and thyroid glands, the type of uterus and placenta, and the position of the nipples.