Carnivora


Carnivora is an order of placental mammals that have specialized in primarily eating flesh. Its members are formally referred to as carnivorans, though some species are omnivorous, like raccoons and bears, and quite a few species like pandas are specialized herbivores. The word 'carnivore' is derived from Latin carō "flesh" and vorāre "to devour", it refers to any meat-eating organism. The order Carnivora is the fifth largest order of mammals and one of the more successful members of the group; it comprises at least 279 species living on every major landmass and in a variety of habitats, ranging the cold polar regions to the hyper-arid region of the Sahara Desert to the open seas. They come in a huge array of different body plans in contrasting shapes and sizes. The smallest carnivoran is the least weasel with a body length of about and a weight of about. The largest is the southern elephant seal, with adult males weighing up to and measuring up to. All species of carnivorans are descended from a group of mammals which were related to today's pangolins, having appeared in North America 6 million years after the Cretaceous–Paleogene extinction event. These early ancestors of carnivorans would have resembled small weasel or genet-like mammals, occupying a nocturnal shift on the forest floor or in the trees, as other groups of mammals like the mesonychians and creodonts were occupying the top faunivorous niche. However, by the time Miocene epoch appeared, most if not all of the major lineages and families of carnivorans had diversified and took over this niche.
Carnivora can be divided into two subclades: the cat-like Feliformia and the dog-like Caniformia which are differentiated based on the structure of their ear bones and cranial features. The feliforms include families such as the cats, the hyenas, the mongooses and the viverrids. The majority of feliform species are found in the Old World, though the cats and one extinct genus of hyena have successfully diversified into the Americas. The caniforms include the dogs, bears, raccoons, weasels, and pinnipeds. Members of this group are found worldwide and with incredible diversity in their diet, behavior, and morphology. Despite this the two groups of carnivorans share several unique traits, one being the presence of the carnassial teeth. In carnivorans the carnassial pair is made up by the fourth upper premolar and the first lower molar teeth. There is variation among the carnassial pair depending on the family. Some species are cursorial and the foot posture in terrestrial species is either digitigrade or plantigrade. In pinnipeds the feet have become flippers where the locomotion is unique in each of the pinniped families.
After primates, carnivorans are arguably the group of mammals of most interest to humans. The dog is noteworthy for not only being the first species of carnivoran to be domesticated, but also the first species of any organism. In the last 10 to 12,000 years humans have selectively bred dogs for a variety of different tasks and today there are well over 400 breeds. The cat is another domesticated carnivoran and it is today considered one of the most successful species on the planet, due to their close proximity to humans and the popularity of cats as pets. Many other species are popular, and they are often charismatic megafauna. Many civilizations have incorporated a species of carnivoran into their culture such as the lion, viewed as royalty. Yet many species such as wolves and the big cats have been broadly hunted, resulting in extirpation in some areas. Habitat loss and human encroachment as well as climate change have been the primary cause of many species going into decline. Four species of carnivorans have gone extinct since the 1600s: Falkland Island Wolf in 1876; the Sea Mink in 1894; the Japanese Sea Lion in 1951 and the Caribbean Monk Seal in 1952. Some species such as the red fox and stoat have been introduced to Australasia that have caused many native species to become endangered or even extinct.

Systematics

Evolution

The order Carnivora belongs to a group of mammals known as Laurasiatheria, which also includes other groups such as bats and ungulates. Within this group the carnivorans are placed in the clade Ferae. Ferae includes the closest extant relative of carnivorans, the pangolins, as well as several extinct groups of mostly Paleogene carnivorous placentals such as the creodonts, the arctocyonians, and mesonychians. The creodonts were originally thought of as the sister taxon to the carnivorans, perhaps even ancestral to, based on the presence of the carnassial teeth. but the nature of the carnassial teeth is different between the two groups. In carnivorans the carnassials are positioned near the front of the molar row, while in the creodonts they are positioned near the back of the molar row. and this suggests a separate evolutionary history and an order-level distinction. In addition recent phylogenetic analysis suggests that creodonts are more closely related to pangolins while mesonychians might be the sister group to carnivorans and their stem-relatives.
The closest stem-carnivorans are the miacoids. The miacoids include the families Viverravidae and Miacidae, and together the Carnivora and Miacoidea form the stem-clade Carnivoramorpha. The miacoids were small, gennet-like carnivoramorphs that occupy a variety of niches such as terrestrial and arboreal habitats. Recent studies have shown a supporting amount of evidence that Miacoidea is an evolutionary grade of canivoramorphs that, while viverravids are monophyletic basal group, the miacids are paraphyletic in respect to Carnivora.
Carnivoramorpha as a whole first appeared in the Paleocene of North America about 60 million years ago. Crowned carnivorans first appeared around 42 million years ago in the Middle Eocene. Their molecular phylogeny shows the extant Carnivora are a monophyletic group, the crown group of the Carnivoramorpha. From there carnivorans have split into two clades based on the composition of the bony structures that surround the middle ear of the skull, the cat-like feliforms and the dog-like caniforms. In feliforms, the auditory bullae are double-chambered, composed of two bones joined by a septum. Caniforms have single-chambered or partially divided auditory bullae, composed of a single bone. Initially the early representatives of carnivorans were small as the creodonts dominated the niches as top apex predators, but by the Miocene most of the extant carnivoran families have diversified and successfully out-competed the creodonts.
The phylogenetic relationships of the carnivorans are shown in the following cladogram:

Classification of the extant carnivorans

In 1758 the Swedish botanist Carl Linnaeus placed all carnivorans known at the time into the group Ferae in the tenth edition of his book Systema Naturae. He recognized six genera: Canis, Phoca, Felis, Viverra, Mustela, Ursus. It wasn't until 1821 that the English writer and traveler Thomas Edward Bowdich gave the group its modern and accepted name.
Initially the modern concept of Carnivora was divided into two suborders: the terrestrial Fissipedia and the marine Pinnipedia. Below is the classification of how the extant families were related to each other after American paleontologist George Gaylord Simpson in 1945:
Since then, however, the methods in which mammalogists use to assess the phylogenetic relationships among the carnivoran families has been improved with using more complicated and intensive incorporation of genetics, morphology and the fossil record. Research into Carnivora phylogeny since 1945 has found Fisspedia to be paraphlyetic in respect to Pinnipedia, with pinnipeds being either more closely related to bears or to weasels. The small carnivoran families Viverridae, Procyonidae, and Mustelidae have found to be polyphyletic:
Below is a table chart of the extant carnivoran families and number of extant species recognized by various authors of the first and fourth volumes of Handbook of the Mammals of the World published in 2009 and 2014 respectively:

Anatomy and physiology

Craniodental region

The canine teeth are usually large and conical. The canines are thick and incredibly stress resistant. All of the terrestrial species of carnivorans have three incisors on the top and bottom row of the dentition. The third molar has been lost. The carnassial pair is made up by the fourth upper premolar and the first lower molar teeth. Like most mammals the dentition is heterodont in nature, though in some species like the aardwolf the teeth have been greatly reduced and the cheek teeth are specialised for eating insects. In pinnipeds the teeth are homodont as they have evolved to grasp or to catch fish, and the cheek teeth are often lost. In bears and raccoons the carnassial pair is secondarily reduced. The skulls are heavily built with a strong zygomatic arch. Often a sagittal crest is present, sometimes more evident in sexual dimorphic species like sea lions and fur seals, though it has also been greatly reduced seen in some small carnivorans. The braincase is enlarged and the frontoparietal is position at the front of it. In most species the eyes are position at the front of the face. In caniforms the rostrum is usually longer with many teeth, where in comparison with felifoms the rostrum is shorter and have fewer teeth. The carnassial teeth in feliforms, however is more sectional. The turbinates are large and complex in comparison to other mammals, providing a large surface area for olfactory receptors.

Postcranial region

Aside from an accumulation of characteristics in the dental and cranial features, not much of their overall anatomy unites them as a group. All species of carnivorans have quadrupedal limbs with usually five digits at the front feet and four digits at the back feet. In terrestrial carnivorans the feet have soft pads. The feet can either be digitigrade seen in cats, hyenas and dogs or plantigrade seen in bears, skunks, raccoons, weasels, civets and mongooses. In pinnipeds the limbs have been modified into flippers. Unlike other marine mammals, such as cetaceans and sirenians which have fully functional tails to help them swim, pinnipeds use their limbs underwater for locomotion. In earless seals they use their back flippers; sea lions and fur seals use their front flippers, and the walrus use all of their limbs. This resulted in pinnipeds having significantly shorter tails. Aside from the pinnipeds, dogs, bears, hyenas, and cats have distinct and recognizable appearances. Dogs are usually cursorial mammals and are gracile in appearance, often relying on their teeth to hold to prey; bears are much larger and rely on their physical strength to forage for food. Cats in comparison to dogs and bears have much longer and stronger frontlimbs armed with retractable claws to hold on to prey. Hyenas are dog-like feliforms that have sloping backs due to their front legs being longer than their hindlegs. The raccoon family as well as the red panda are small, bear-like carnivorans with long tails. The other small carnivoran families Nandiniidae, Prionodontidae, Viverridae, Herpestidae, Eupleridae, Mephitidae and Mustelidae have through convergent evolution maintained the small, ancestral appearance of the miacoids, though there is some variation seen such as the robust and stout physicality of badgers and the wolverine. Male carnivorans usually have bacula, though they are absent in hyenas and binturongs.
Depending on the environment the species is, the length and density of their fur varies. In warm climate species the fur is often short in length and lighter. In comparison to cold climate species the fur is either dense or long, often with an oily substance to keep them warm. The pelage coloration comes in many colors, often including black, white, orange, yellow, red, and many shades of gray and brown. There can be colored patterns too, such striped, spotted, blotched, banded, or otherwise boldly patterned. There seems to be a correlation between habitat and color pattern as for example spotted or banded species tend to be found in heavily forested environments. Some species like the grey wolf is a polymorphic species with different individual variation in colors. The arctic fox and the stoat the fur goes from white and dense in the winter to brown and sparse in the summer. In pinnipeds, polar bears, and sea otters have a thick insulating layer of blubber to help maintain their body temperature.