The diverse
order Carnivora (or sometimes /ˌkɑrnɪˈvɔərə/; from
Latin carō (stem
carn-) "flesh", +
vorāre "to devour") includes over 260 species of
placental mammals. Members of the order are called
carnivorans, while the word "
carnivore" can refer to a meat-eating animal of any type. Carnivorans are the most diverse in size of any mammalian order, ranging from the
Least Weasel (
Mustela nivalis), at as little as 25 grams and 11 cm (4.3
in), to the
Polar bear (
Ursus maritimus), which can weigh up to 1000 kg (2200 lb), to the
Southern Elephant Seal, adult males of which average 2,270 kg (5,000
lb) and measure 4.2 m (13.9
ft) (and may grow considerably larger).
The first carnivoran was a
carnivore, and nearly all carnivorans today primarily eat meat. Some, such as
cats,
pinnipeds, and
weasels, are almost completely carnivorous. Others, such as
bears, are more
omnivorous.
The
Giant Panda is almost exclusively an
herbivore, but it occasionally eats fish, eggs and insects.
Carnivorans have teeth and claws adapted for catching and eating other animals. Their eyes point forward. Many carnivorans hunt in packs and are social.
Carnivorans apparently evolved in North America out of members of the family
Miacidae (miacids)
c 42 million years ago. They soon split into catlike and doglike forms (
feliformia and
caniformia).
Distinguishing features
Carnivorans are primarily
terrestrial and usually have strong sharp
claws, with never less than four toes to each foot, and well-developed prominent
canines and
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 are blade-like teeth that 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
Canoidea superfamily –
Canidae (dogs),
Mephitidae (skunks and stink badgers)
Mustelidae (weasels),
Procyonidae (raccoons),
Ursidae (bears),
Otariidae (eared seals),
Odobenidae (walrus), and
Phocidae (earless seals) [thelast three families formally classified in the suborder
Pinnipedia] and the extinct family
Amphicyonidae (bear-dogs) - are characterized by having a non-chambered or partially chambered
auditory bullae, non-retractable claws, and well-developed
baculum. Most species are rather simply colored, lacking the flashy spotted or rosetted coats of 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
Feloidea superfamily –
Felidae (cats),
Herpestidae (mongooses),
Hyaenidae (hyenas),
Viverridae (civets), and
Eupleridae (Malagasy carnivores), 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 due to the fact that these species tend to range in tropical habitats, although a few species do inhabit temperate and subarctic habitats. Many are arboreal or semi-arboreal, and the majority are digitigrade. Diet tends to be more strictly carnivorous, especially in the Felidae family. They have fewer teeth and shorter skulls, with much more specialized carnassials meant for shearing meat. Felidae claws are retractile. The terminal phalange with the claw attached folds back in the fore-foot into a sheath by the outer side of the middle phalange of the digit, and is retained in this position when at rest by a strong elastic ligament. In the hind-foot the terminal joint or phalange is retracted on to the top, and not the side of the middle phalange. Deep flexor muscles straighten the terminal phalanges so that the claws protrude from their sheath, and the soft "velvety" paw becomes suddenly converted into a formidable weapon of offence. The habitual retraction of the claws preserves their points from wear.
The
Pinnipedia superfamily (walruses, seals, and sea lions) are medium to large (to 6.5 m) aquatic mammals. Pinnipeds are marine Carnivora and therefore need to have a relatively large body to retain heat. They need a low surface area to body mass ratio to minimize heat loss due to conduction because water conducts heat well. The body is usually insulated with a thick layer of fat called
blubber and usually 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 at extreme depths (600 meters for the
Weddell seal) and they can remain underwater for long periods of time, sometimes over 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 is 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.
Skull structure
Members of Carnivora have a characteristic skull shape with relatively large brains encased in a heavy skull. The skull has a highly developed
zygomatic arch just behind the
maxilla (common to all mammals and their
cynodont forebears), and they've
ossified external auditory bullae. Feloidea have a two-chambered auditory bullae. In addition to allowing extra room for the passage of muscles to work the lower jaw, the zygomatic arch also allows for differentiation of separate muscle groups to be involved in biting and chewing.
Masseters attach from the dentary (specifically, the
masseteric fossa) to the zygomatic arch and onto the maxilla in front of the arch, providing crushing force. The
temporalis attaches from the dentary (specifically, the
coronoid process) to the side of the braincase, providing torque about the axis of jaw articulation. In comparing the skulls of carnivores and herbivores, it can be seen that the shearing force of the temporalis is somewhat more important to carnivores, which have more room on the braincase (this isn't unrelated to carnivoran intelligence) and commonly develop a
sagittal crest (running from posterior to anterior on the skull) providing yet additional room for temporalis attachment. Carnivoran jaws can only move on a vertical axis, in an up-and-down motion, and can't move from side-to-side. The jaw joint in carnivores tends to lie within the plane of tooth occlusion; an arrangement that further emphasizes shearing (as in a pair of scissors). In herbivores, the crushing force of the masseters is relatively more important than is shearing. The jaw joint is generally well above the plane of tooth occlusion, allowing extra room for masseteric attachment on the dentary and causing the rotation of the lower jaw to be translated into straight-ahead crushing force between the teeth of the upper and lower jaws.
Physiology
Carnivora have a simple stomach designed to digest primarily meat, as compared to the elaborate digestive systems of herbivorous animals which are necessary to break down tough, complex plant fibers. The
caecum is either absent or short and simple, and the colon isn't
sacculated or much wider than the small intestine. Most species of Carnivora are, to some degree, omnivorous, except the Felidae, which are obligate carnivores. Most have highly-developed senses, especially vision and hearing, and often a highly acute sense of smell in many species, such as in the Canoidea. They are excellent runners: some long-distance runners, but more commonly sprinters. Even bears and raccoons, although seemingly slow and clumsy, are capable of remarkable bursts of speed.
Diet specializations
Carnivorans include
carnivores,
omnivores, and even a few primarily
herbivorous species, such as the
giant panda. Important teeth for carnivorans are the large, slightly recurved canines, used to dispatch prey, and the carnassial complex, used to rend meat from bone and slice it into digestible pieces. Dogs have molar teeth behind the carnassials for crushing bones, but cats have only a greatly reduced, functionless molar behind the carnassial in the upper jaw. Cats will strip bones clean but won't crush them to get the marrow inside. Omnivores, such as bears and raccoons, have developed blunt, molar-like carnassials. Carnassials are a key adaptation for terrestrial vertebrate predation; all other placental orders are primarily herbivores, insectivores, or aquatic.
Reproductive system
Carnivora tend to produce a single litter annually, but some produce multiple litters a year, and larger carnivores like bears have gaps of 2-3 years between litters. The average
gestation period lies between 50-115 days, although the ursids and mustelids have delayed implantation, thus extending the gestation period 6-9 months beyond the normal period. Litter sizes are usually small, ranging from 1-13 young, which are born with underdeveloped eyes and ears. In most species, the mother has exclusive or at least primary care of the offspring. Many species of carnivores are
solitary, but a few are
gregarious.
Phylogeny
Carnivorans evolved out of members of the family
Miacidae (miacids). The transition from Miacidae to Carnivora was a general trend in the middle and late
Eocene with taxa from both North America and Eurasia involved. The divergence of carnivorans from other miacids, as well as the divergence of the the two
clades within Carnivora,
Caniformia and
Feliformia, is now inferred to have happened in the middle
Eocene (ca. 42 million years ago). Traditionally the
Viverravidae (viverravids) had been thought to be the earliest carnivorans with fossil records first appearing in the
Paleocene of North America about 60 million years ago, but recently described evidence from
cranial morphology now places them outside the order Carnivora. Traditionally, some
paleontologists considered the viverravids to be ancestral to the
aeluroid carnivorans (
felids,
hyaenids,
herpestids and
viverrids), but this is now doubted.
The Miacidae isn't a
monophyletic group, but a
paraphyletic array of stem taxa. Traditionally, the Miacidae and the Viverravidae had been classified in a third, extinct paraphyletic superfamily, the
Miacoidea, from which the direct ancestors of both Carnivora and
Creodonta were thought to have arisen. Today Carnivora is restricted to the
crown group, and Carnivora and
miacoids are grouped together in the clade
Carnivoramorpha, and the miacoids are regarded as basal carnivoramorphs. Based on dental features and braincase sizes, it's now known that Carnivora must have evolved from a form even more primitive than Creodonta and thus these two orders may not even be sister groups. The Carnivora, Creodonta,
Pholidota, and a few other extinct orders are informally grouped together in the clade
Ferae. Older classification schemes divided the order into two suborders:
Fissipedia (which included the families of primarily land Carnivora) and
Pinnipedia (which included the
true seals,
eared seals, and
walrus). However, it's now recognized that the Fissipedia is a paraphyletic group and that the pinnipeds were not the sister group to the fissipeds but rather had arisen from among them.
Carnivora are generally divided into the suborders Feliformia (cat-like) and Caniformia (dog-like), the latter of which includes the
pinnipeds. The pinnipeds are part of a clade, known as the
Arctoidea, which also includes the
Ursidae (bears) and the superfamily
Musteloidea. The Musteloidea in turn consists of the
Mustelidae (mustelids: weasels),
Procyonidae (procyonids: raccoons),
Mephitidae (skunks) and
Ailurus. The oldest caniforms are the
Miacis species
Miacis cognitus, the
Amphicyonidae (Bear-dogs) such as
Daphoenus, and
Hesperocyon (of the family Canidae, subfamily Hesperocyoninae). Hesperocyonine
canids first appeared in North America and the earliest species is currently dated at 39.74 Ma, but they were not represented in Europe until well into the
Miocene, and not into Asia and Africa until the
Pliocene.
Miacis and Amphicyonidae were the first of the caniforms to split from the others and are sometimes considered to be sister groups to Ursidae, but the exact closeness of Amphicyonidae and Ursidae, as well as Arctoidae to Ursidae, is still uncertain. The
Canidae (
wolves,
coyotes,
jackals,
foxes and
dogs) are generally considered to be the sister group to Arctoidea. The Ursidae first occur in North America in the Late Eocene (ca. 38 million years ago) as the very small and graceful
Parictis that had a skull only 7 cm long. Like the canids, this family doesn't appear in
Eurasia and Africa until the Miocene. The other caniform families Amphicyonidae, Mustelidae and Procyonidae occur in both the Old World and the New World by the Late Eocene and Early
Oligocene. Its position as a Carnivora is currently unstable. Other studies indicate that
Barbourofelids forms a separate family, which is closely related to the true felids instead of being related to the Nimravids. Recognizable Nimravid fossils date from the late Eocene (37 mya), from the Chadronian White River Carnivora Formation at Flagstaff Rim, Wyoming. Nimravid diversity appears to have peaked about 28 mya. The
hypercarnivorous (strictly meat-eating) nimravid feliforms were extinct in North America after 26 mya and felids didn't arrive in North America until the early middle Miocene (16 mya).
It has been suggested that canids evolved hypercarnivorous morphologies because feliforms were absent during this period (the "cat-gap," 26-16 mya), however recent data doesn't support this hypothesis. Hypercarnivore feliforms (felids and nimravids) occupied an area that canids didn't and where felids, nimravids, and hypercarnivorous creodonts are found. Hypercarnivorous canids were present before the disappearance of the nimravids, and all went extinct before the appearance of felids. Following the extinction of nimravids, only three taxa originated, two of which were relatively small in body size. Disparity increased during the "cat-gap" even with the extinction of the hypercarnivorous extremes. This was due to the extinction of morphological intermediates, and because carnivorans began to occupy hypocarnivorous (non-meat-specialist) morphospace for the first time in North America. Procyonids didn't arrive in North America until the early Miocene, and "modern" ursids (for example,
Ursinae), didn't arrive until the late Miocene. Extinct lineages of Ursidae were present in North America from the late Eocene through the Miocene and Amphicyonid (Bear-dogs) were present during this period as well but occupied a morphospace generally shared with canids and not in close proximity to ursids. A large question remains as to why there was a progressive decline in hypercarnivorous carnivoramorphans during the late Oligocene/early Miocene. During this period all hypercarnivorous forms disappeared from the fossil record, including hypercarnivorous feliforms, canids, and mustelids. One possible explanation is climate change. Earth was gradually cooling after the late Paleocene, and over a period spanning the Eocene/Oligocene boundary there was a dramatic climatic cooling event occurred.
A recent study finally resolves the exact position of
Ailurus: the Red Panda is neither a procyonid nor an ursid, but forms a monotypic family with the other musteloids as its closest living relatives. The same study also shows that the mustelids are not a primitive family, as was once thought. Their small body size is a secondary trait — the primitive body form of the arctoids was large, not small. Recent molecular studies also suggest that the endemic Carnivora of
Madagascar, including three genera usually classed with the
civets and four genera of
mongooses classed with the Herpestidae, are all descended from a single ancestor. They form a single sister
taxon to the Herpestidae. The
hyenas are also closely related to this clade.
Classification
Phylogenetic Tree
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