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The Carnivora is the result of a great radiation of mammals that ate meat. But not all meat eaters are in this order; carnivorous species can certainly be found among, for example, the marsupials, bats, primates, cetaceans, and others. It is also true that not all Carnivora are carnivorous; some, such as bears and raccoons, are decidedly omnivorous, and at least one, the panda, is primarily vegetarian. But the Carnivora are a clearly monophyletic group that is first known from the late Paleocene and whose primitive food habits were carnivorous.

Most members of the Order Carnivora can be recognized by their enlarged fourth upper premolar and first lower molar, which together form an efficient shear for cutting meat and tendon. These teeth are referred to as the carnassial pair. The exceptions are a few forms, such as bears, raccoons, and seals, in which these teeth are secondarily modified.

Carnivores tend to be medium-sized animals; too small and they couldn't find enough within their capacity to kill; too large and they wouldn't be able to satisfy their appetites. Most have very acute senses. Vision and hearing are excellent in many carnivores, and the sense of smell is often remarkable. Most have relatively large brains. Many are excellent runners. A few are good long-distance runners, but more commonly, Carnivora are rapid sprinters that use stealth to approach their prey, then overcome it with a short, violent rush. A few, like bears and raccoons, seem relatively slow or clumsy, but even these species are capable of remarkable bursts of speed. Even the long-distance runners don't have the highly modified and relatively inflexible skeletons and movement patterns of cursorial herbivores like artiodactyls; this is probably related to the often unpredictable demands that catching and killing large prey place on their skeletons.

The skulls of Carnivora are highly varied in form. Most have a well-defined, transverse glenoid fossa, and the dominant motion of the jaw is in the dorsal-ventral direction. The primary muscle powering the jaw is the temporal, and sagittal crest associated with the temporal is commonly a conspicuous part of the surface of the skull. Carnivores also have a strong zygomatic arch and a relatively large braincase. The auditory bullae and the turbinals also tend to be large and complex.

Besides usually having carnassials, almost all Carnivora retain the primitive number of incisors (3/3); an exception is the sea otter, which has 2/3. The outer (3rd) incisor is often relatively large and canine-like. The canines are large and conical. The number of teeth behind the carnassials varies considerably, from 1/1 in some cats to 4/4 in bears (would be more in some pinnipeds, but they have no carnassials). All teeth are rooted and diphyodont.

All Carnivora have a simple stomach.

Marine carnivores are a special group, referred to as the "pinnipeds" (terrestrial carnivores, in contrast, are called the "fissipeds"). Pinnipeds are found in the Otariidae and Phocidae families. All pinnipeds are large, perhaps because water conducts heat well and large animals have a low surface area to body mass ratio, which minimizes heat loss due to conduction. Their bodies are insulated by a thick layer of fat called blubber. In all species, the external ears are small or absent, the external genitalia and nipples are hidden in slits or depressions in the body, and the tail is very small. The forelimbs and hindlimbs are transformed into paddles. In both, the proximal limb elements (humerus and femur) remain within the body, and other aspects of the limbs, limb girdles, and spine are highly specialized for swimming. Most species have a relatively short rostrum, and the orbits are large. The cheek teeth are usually homodont (no differentiation along the toothrow), and the teeth are usually shaped like simple cones. These animals are capable of diving to extreme depths (600 m in the case of the Weddell seal) and remaining under water for astonishing periods (over an hour, although most dives are much shorter). It is easier to maintain small pinnipeds in the lab than cetaceans, and consequently their physiological adaptations for diving have been studied extensively.

While most systematists agree that terrestrial carnivores can be divided into two groups, the dog-like (caniform) and cat-like (feliform) families, there is considerable disagreementover the relationships of carnivore families, especially with respect to the pinnipeds. Currently, the most strongly supported scheme places pinnipeds as a monophyletic group within the caniform lineage, most closely related to bears, red pandas, and raccoons. The sister group to this clade is the family Mustelidae, and the canids appear as an early offshoot of the caniforms. Some authorities, however, consider the pinnipeds to be monophyletic and basal to all living carnivores (feliform and caniform), and place it in a separate order, the Pinnipedia. Others suggest that marine species were derived at least twice, with one lineage (perhaps derived from ursids) leading to the sea lions (and walruses, although even this is debated) and the other (from mustelids) to the true seals.

We recognize 11 families and around 270 species among the living Carnivora. They are distributed across the world, in all major land masses (except possibly Australia, where the only terrestrial Carnivora, the dingo, may have been brought by man) and in all oceans.

Superfamily Canoidea

Family Canidae
Family Ursidae 
Family Otariidae
Family Odobenidae
Family Procyonidae
Family Mustelidae
Family Phocidae

Superfamily Feloidea

Family Viverridae 
Family Herpestidae
Family Hyaenidae 
Family Felidae

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