Carnivora

**Carnivora** is a diverse scrotiferan order that includes over 280 species of placental mammals. Its members are formally referred to as **carnivorans**, whereas the word "carnivore" (often popularly applied to members of this group) can refer to any meat-eating organism. Carnivorans are the most diverse in size of any mammalian order, ranging from the least weasel (*Mustela nivalis*), at as little as 25 g (0.88 oz) and 11 cm (4.3 in), to the polar bear (*Ursus maritimus*), which can weigh up to 1,000 kg (2,200 lb), to the southern elephant seal (*Mirounga leonina*), whose adult males weigh up to 5,000 kg (11,000 lb) and measure up to 6.7 m (22 ft) in length.

Carnivorans have teeth and claws adapted for catching and eating other animals. Many hunt in packs and are social animals, giving them an advantage over larger prey. Some carnivorans, such as cats and pinnipeds, depend entirely on meat for their nutrition. Others, such as raccoons and bears, are more omnivorous, depending on the habitat. The giant panda is largely a herbivore, but also feeds on fish, eggs and insects. The polar bear subsists mainly on seals.

Carnivorans evolved in North America out of members of the family Miacidae (miacids) about 42 million years ago. They soon split into cat-like and dog-like forms (Feliformia and Caniformia). Their molecular phylogeny shows the extant Carnivora are a monophyletic group, the crown group of the Carnivoramorpha.

## Distinguishing features

Most carnivorans are terrestrial; they usually have strong, sharp claws, typically with five, but never fewer than four, toes on each foot, and well-developed, prominent canine teeth, cheek teeth (premolars, and molars) that generally have cutting edges. The last premolar of the upper jaw and first molar of the lower are termed the  carnassials or sectorial teeth. These blade-like teeth occlude (close) with a scissor-like action for shearing and shredding meat. Carnassials are most highly developed in the Felidae and the least developed in the Ursidae. Carnivorans have six incisors and two conical canines in each jaw. The only two exceptions to this are the sea otter (*Enhydra lutris*), which has four incisors in the lower jaw, and the sloth bear (*Melursus ursinus*), which has four incisors in the upper jaw. The number of molars and premolars is variable between carnivoran species, but all teeth are deeply rooted and are diphyodont. Incisors are retained by carnivorans and the third incisor is commonly large and sharp (canine-like). Carnivorans have either four or five digits on each foot, with the first digit on the forepaws, also known as the dew claw, being vestigial in most species and absent in some.

The superfamily Canoidea (or suborder Caniformia) – Canidae (wolves, dogs and foxes), Mephitidae (skunks and stink badgers), Mustelidae (weasels, badgers, and otters), Procyonidae (raccoons), Ursidae (bears), Ailuridae (red panda), Otariidae (eared seals), Odobenidae (walrus), and Phocidae (earless seals) (the last three families formerly classified in the superfamily Pinnipedia) and the extinct family Amphicyonidae (bear-dogs) – are characterized by having nonchambered or partially chambered auditory bullae, nonretractable claws, and a well-developed baculum. Most species are rather plain in coloration, lacking the flashy spotted or rosetted coats like many species of felids and viverrids have. This is because Canoidea tend to range in the temperate and subarctic biomes, although Mustelidae and Procyonidae have a few tropical species. Most are terrestrial, although a few species, like procyonids, are arboreal. All families except the Canidae and a few species of Mustelidae are plantigrade. Diet is varied and most tend to be omnivorous to some degree, and thus the carnassial teeth are less specialized. Canoidea have more premolars and molars in an elongated skull.

The superfamily Feloidea (or suborder Feliformia)– Felidae (cats), Prionodontidae (Asiatic linsangs), Herpestidae (mongooses), Hyaenidae (hyenas), Viverridae (civets), and Eupleridae (Malagasy carnivorans), as well as the extinct family Nimravidae (paleofelids) – often have spotted, rosetted or striped coats, and tend to be more brilliantly colored than their Canoidean counterparts. This is because these species tend to range in tropical habitats, although a few species do inhabit temperate and subarctic habitats. Many are arboreal or semiarboreal, and the majority are digitigrade. Diet tends to be more strictly carnivorous, especially in the family Felidae. They have fewer teeth and shorter skulls, with much more specialized carnassials meant for shearing meat. Feliformia claws are often retractile, or rarely, semiretractile. The terminal phalanx, with the claw attached, folds back in the forefoot into a sheath by the outer side of the middle phalanx of the digit, and is retained in this position when at rest by a strong elastic ligament. In the hindfoot, the terminal joint or phalanx is retracted on to the top, and not the side of the middle phalanx. Deep flexor muscles straighten the terminal phalanges, so the claws protrude from their sheaths, and the soft "velvety" paw becomes suddenly converted into a formidable weapon. The habitual retraction of the claws preserves their points from wear.

The superfamily Pinnipedia (walruses, seals, and sea lions), now considered to be part of Caniformia, are medium to large (to 6.5 m) aquatic mammals. Being homeothermic (warm-blooded) marine mammals, pinnipeds need a low surface area to body mass ratio. Otherwise, they would suffer from excessive heat loss due to water's high capacity for heat conduction. The body is usually insulated with a thick layer of fat called blubber and typically covered with hair. The digits are not separate, but connected by a thick web that forms flippers for swimming; thus, the forelimbs and hindlimbs are transformed into paddles. This enables them to dive to extreme depths (600 m for the Weddell seal). They can remain underwater for long periods of time, sometimes an hour or more, but most dives are usually short. The facial region of skull is relatively small, with pinnae very small or lacking, and the vibrissae are well developed. The molariform teeth are mostly homodont and the canines are well developed. The tail is very short or absent, the ears are small or absent as well, and the external genitalia are hidden in slits or depressions in the body.