Order Carnivora is composed of predaceous mammals with large canine teeth and a car-nassial mechanism (specialized shearing blades formed by the occlusion of the last upper premolar and first lower molar). Interactions between the array of carnivore species and the single living human species are mixed. Many carnivores are trapped or hunted for their coats and flesh. Pinnipeds (walruses and seals) have been an important source of fur, food, oil, and ivory. For the last 11,000 years, populations of the wolf (Canis lupus) have been domesticated into more than 400 breeds of dog. Since at least 3500 B.C.E., descendants of the African wild cat (Felis sylvestris lybica) have been cultivated into thirty to forty breeds of domestic cat. Dogs and cats have been bred primarily to serve as human companions, though they are sometimes utilized to perform work and as a source of meat. The popularity of these animals as pets has a significant economic impact: revenue is generated by the manufacturing and sale of goods, food, and medical care for the animals, but control and housing of strays in some countries is costly. Populations of large predators such as the wolf, puma, lion, leopard, and jaguar are reduced or eliminated from ecosystems where they engender fear and compete with humans for domestic animal stock (cattle and sheep). Many carnivores, especially all species of cats, are deeply appreciated for their aggressive and focused predatory instincts, graceful form, fluid movement, and aesthetic beauty.
The evolutionary adaptive radiation of most mammalian carnivores may have been a response to an expanding diversity of herbivores, their primary food source. There were only two groups of Early Cenozoic terrestrial carnivorous mammals: Order Creodonta and Order Carnivora. Creodonta (consisting of two families) first appeared in the Late Pale-ocene, were common throughout the Eocene in North America, Europe, Asia, and Africa, and persisted until the Late Miocene in tropical habitats in Asia and Africa. Creodonts had specialized shearing surfaces formed from either the first upper and second lower molar or second upper and third lower (unlike the pattern typical of living carnivores). They were the typical carnivores of the Early Cenozoic but were not ancestral to the modern Order Carnivora.
Members of the extinct families Viverravi-dae and Miacidae, Order Carnivora, lived from the Early Paleocene to the Late Eocene in North America, Europe, and Asia. They are considered by paleontologists to be ancestral to the modern carnivores. They were small-bodied (ranging from the size of a weasel to that of a house cat) and possessed the modern car-nassial formed by the last upper premolar and first lower molar. The 280 species of living carnivores are arranged in 115 genera, twelve families, and two suborders, Feliformia and Caniformia. The Feliformia consists of the families Felidae (cats), Viverridae (civets and genets), Herpestidae (mongooses), and Hyaenidae (hyenas and aardwolf). Families Canidae (wolves, jackals, foxes, and dogs), Mustelidae (weasels, badgers, and otters), Mephitidae (skunks and stink badgers), Pro-cyonidae (raccoons, ringtails, coatis, kinkajou, olingos, and lesser panda), Ursidae (bears and giant panda), Odobenidae (walrus), Phoci-dae (earless seals), and Otariidae (eared seals, fur seals, and sea lions) compose the Cani-formia. The latter three families are some times placed in Order Pinnipedia, but all recent studies incorporating morphology and biochemical data indicate the pinnipeds to be a monophyletic group that is most closely related to the bears (Ursidae). Natural distribution of terrestrial species include most of the planet's land areas except Australia, New Guinea, New Zealand, Antarctica, and many oceanic islands. The dingo, a breed of dog, forms wild populations in Australia and New Guinea but was introduced there by prehistoric human settlers. Walruses, seals, and sea lions are found predominantly along ice fronts and the coastlines of polar and temperate oceans and adjoining seas; some occur in tropical regions and large inland lakes and seas.
A spectacular range in body size exists within modern carnivores. Among terrestrial species, the least weasel (Mustela nivalis) is the smallest, with a head and body up to 18 cm long and weighing up to 70 gm. The largest is the grizzly or brown bear (Ursus arctos), with a head and body up to 280 cm long and attaining a weight of up to 780 kg; Ursus arctos is the largest living land carnivore. The smallest pinnipeds are in the family Phocidae, such as the ringed seal (Phoca hispida), with a head and body averaging 141 cm and weighing up to 128 kg. Also in the same family is the southern elephant seal (Mirounga leonina), which is the largest living pinniped, with a head and body up to 600 cm long and weighing up to 3,700 kg. Pinnipeds are generally larger than terrestrial carnivores, an adaptation allowing energy conservation in cold habitats. Large size is an effective adaptation to cold because it favors heat conservation by decreasing surface area relative to body mass.
Most species of Felidae, Viverridae, Her-pestidae, Mustelidae, Canidae, and the polar bear prey on live animals. Their entire body structure and behavior define "predator" from a human perspective. Using their acute hear ing, remarkable sense of smell, and excellent vision, they capture prey by pouncing from a concealed position (most cats); stalking, followed by a swift rush (weasels and lions), a long chase (wolves); or a short burst of great speed (cheetahs). All species in these families have impressive canines and prominent carnassials, but this shearing mechanism is most highly developed in the cats, which subsist almost entirely on flesh and are the most proficient of all carnivoran predators. Many felid species kill prey as large as themselves, and some take down prey several times their own weight (puma preying on mule deer, for example). Members of Hyaenidae may prey primarily on large mammals (spotted hyena), scavenge remains at large mammal kills (brown and striped hyenas), or consume only termite larvae and other insects (aardwolf). A few species of viverrids and herpestids include fruit in their diet, and members of the Mephitidae, Procyonidae, and Ursidae are omnivorous. The carnassial configuration is least developed in procyonids and ursids.
Different techniques are used to kill prey. The long-tailed weasel (Mustela frenata) kills young rabbits by repeatedly biting the back of the rabbit's head and penetrating the skull again and again. Lions kill small prey with a slap of the paw; larger prey is seized by the throat and strangled or suffocated by the lion clamping its jaws over mouth and nostrils. The sea otter (Enhydra lutris) eats slow-moving fish, sea urchins, abalone, crabs, and mol-lusks. Pinnipeds forage on the most abundant sea food encountered, mostly krill (small shrimplike animals), other crustaceans, squid, mol-lusks, and fish. Leopard seals are the only pinnipeds that prey on other mammals and birds, capturing crabeater seals and penguins, and also eating krill, fish, and squid. The crabeater seal eats mostly krill and has specialized, notched teeth that filter the krill from the
seawater. Walruses feed primarily on clams and mussels.
Terrestrial carnivores are nocturnal, diurnal, or active day and night. Most species are adapted to either living on the ground (terrestrial) or in trees (arboreal), though some utilize both substrates. Leopards capture their prey on the ground and climb trees to store or eat it. Sulawesian palm civets (Macrogalidia musschenbroekii), coatis (Nasua), and martens, fisher, and sable (Martes) pursue prey on the ground and in trees. The tayra (Eira barbara) lives in neotropical forests and is a swift and agile runner, climber, and swimmer. The amphibious otters are excellent swimmers and divers, feeding on fish, frogs, crabs, and mol-lusks. The sea otter spends nearly its entire life in the ocean, rarely farther than 1 km from shore. Although clumsy on land, pinnipeds are superb divers and swimmers, foraging in the water but hauling out onto land or ice isolated from humans and other predators to mate and bear young.
Terrestrial carnivores are solitary (leopards), live in pairs (many species of canids), or form small aggregations (lion prides, for example). Lions even hunt in groups, which usually consist of females. Most species produce a single litter each year; others bear young up to three times during the year, and some larger species give birth at intervals of several years. Gestation periods range from 49 to 113 days in most species; litter size ranges from one to thirteen. Bears and some mustelids exhibit delayed implantation of fertilized eggs, so the period between mating and birth is much longer than average. Newborns are blind and dependent upon adults (altricial), and they require long periods of parental care and instruction. Some temperate species hibernate, whereas others follow their ungulate prey as they migrate from mountains into valleys before winter.
Pinnipeds exhibit a range of social behavior. At one end is the Ross seal (Ommatophoca rossi), which lives alone during the winter; at the other is the gregarious walrus, which forms breeding colonies of several thousand individuals. Seals, fur seals, sea lions, and walruses (Otariidae and Odobenidae) are polygamous; earless seals (Phocidae) are monogamous. All species mate once each year; gestation ranges from eight to fifteen months, and one (or rarely, two) young are born on land or ice. Delayed implantation of the fertilized egg occurs in several species, possibly an adaptation allowing synchronized births in colonial species. Newborn pups can swim but do not develop sufficient blubber for insulation and buoyancy for several months. Some pinnipeds migrate to foraging and breeding areas. Northern elephant seals (Mirounga angustirostris) may migrate up to 21,000 km in a year, the greatest distance documented for any mammal.
In addition to the carnassial mechanism and large conical, recurved canines, carnivores are characterized by rooted teeth, a large braincase containing well-developed cerebral hemispheres, sensitive hearing, acute olfaction, and astute eyesight. Strong facial muscles are attached to a robust cranium and mandible. The mandible is articulated to the cranium in such a way that it can move only up and down (so the mouth opens and shuts), with no rotary and extremely limited transverse movements. Carnivores, unlike most artiodactyls, have a simple stomach. Species of Canidae, Felidae, and Hyaenidae walk only on their toes (digitigrade); members of Ursidae and Procyonidae walk on their soles, with the heels touching the ground (plantigrade). Cursorial (running) pursuit of prey is highly developed in some canids (wolves, for example) and cats (cheetahs), but limited in plantigrade species. The primitive number of five digits on front and hind feet is usual in Carnivora, except for the hyenas and the African hunting dog (Lycaon pic-tus), which have four digits on each front and hind foot. The digits of otters are connected by webbing, except for the clawless otters (Aonyx), in which the webbing is confined to the base of the digits or is absent altogether. These otters locate crabs, mollusks, and frogs in mud or under stones with their sensitive and dexterous front paws. Tails may be stubby (bears) or long (as in most terrestrial carnivores); only the arboreal Indo-Malayan bin-turong (Arctictis binturong) and neotropical kinkajou (Potos flavus) have prehensile tails. Ears range from small to large relative to the size of the head. The fennec fox (Fennecus zerda) is the smallest member of Canidae but has the largest ears relative to body size. Some species of weasels living at northern latitudes molt from a summer brown coat into winter white fur.
The body is streamlined and torpedo-shaped in pinnipeds, which creates minimal drag during swimming. Ears are small or absent; the ears and slitlike nostrils are closed while underwater but voluntarily opened out of water. Front and hind feet are modified as flippers formed by broadly webbed and oarlike digits; only those parts of the limbs beyond the elbow and knee protrude from the body surface. The tail is absent or rudimentary. These are all external adaptations to an aquatic (primarily marine) existence. Other adaptations are reflected by the shortened face, flattened head, eyes set deep within protective layers of fat, and thick but flexible neck. The interlocking processes (zygapophyses) of the vertebrae and no clavicle allow pinnipeds to bend farther backward than most mammals. These features allow great maneuverability while pursuing prey, as well as the ability to absorb the shock of ocean waves.
—Mary Ellen Holden
See also: Adaptive Radiation; Alien Species; Coastal Wetlands; Coloniality; Ecosystems; Endangered Species; Extinction, Direct Causes of; International Trade and Biodiversity; Intertidal Zone; Mammalia; Oceans; Plankton; Positive Interactions
Gittleman, John L., ed. 1989. Carnivore Behavior, Ecology, and Evolution. Ithaca, NY: Comstock; King, Judith E. 1983. Seals of the World. Ithaca, NY: Cornell University Press; McKenna, Malcolm C., and Susan K. Bell. 1997. Classification of Mammals above the Species Level. New York: Columbia University Press; Nowak, Ronald M. 1999. Walker's Mammals of the World, 6th ed. Vol. 2. Baltimore: Johns Hopkins University Press; Schaller, George B. 1967. The Deer and the Tiger. Chicago: University of Chicago Press; Schaller, George B. 1972. The Serengeti Lion: A Study of Predator-Prey Relations. Chicago: University of Chicago Press; Vaughan, Terry A., James M. Ryan, and Nicholas J. Czaplewski. 2000. Mammalogy, 4th ed. Orlando, FL: Harcourt; Wilson, Don E., and Sue Ruff, eds. 1999. The Smithsonian Book of North American Mammals. Washington, DC: Smithsonian Institution Press.
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