Bear

Bear

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Bears are mammals of the family Ursidae. Bears are classified as caniforms, or doglike carnivorans, with the pinnipeds being their closest living relatives. Although there are only eight living species of bear, they are widespread, appearing in a wide variety of habitats throughout the Northern Hemisphere and partially in the Southern Hemisphere. Bears are found in the continents of North America, South America, Europe, and Asia.

Common characteristics of modern bears include a large body with stocky legs, a long snout, shaggy hair, plantigrade paws with five nonretractile claws, and a short tail. While the polar bear is mostly carnivorous and the giant panda feeds almost entirely on bamboo, the remaining six species are omnivorous, with largely varied diets including both plants and animals.

With the exceptions of courting individuals and mothers with their young, bears are typically solitary animals. They are generally diurnal, but may be active during the night (nocturnal) or twilight (crepuscular), particularly around humans. Bears are aided by an excellent sense of smell, and despite their heavy build and awkward gait, they can run quickly and are adept climbers and swimmers. In autumn some bear species forage large amounts of fermented fruits which affects their behaviour. Bears use shelters such as caves and burrows as their dens, which are occupied by most species during the winter for a long period of sleep similar to hibernation.

Bears have been hunted since prehistoric times for their meat and fur. To this day, they play a prominent role in the arts, mythology, and other cultural aspects of various human societies. In modern times, the bear's existence has been pressured through the encroachment on its habitats and the illegal trade of bears and bear parts, including the Asian bile bear market. The IUCN lists six bear species as vulnerable or endangered, and even least concern species such as the brown bear are at risk of extirpation in certain countries. The poaching and international trade of these most threatened populations is prohibited, but still ongoing.

Etymology

The English word "bear" comes from Old English bera and belongs to a family of names for the bear in Germanic languages, in origin from an adjective meaning "brown".In Scandinavia the word for bear is björn (or bjørn), and is a relatively common given name for males. The use of this name is ancient and has been found mentioned in several runestone inscriptions.In Germanic culture, the bear was a symbol of the warrior, as evident from the Old English term beorn which can take the meaning of both "bear" and "warrior".

The reconstructed Proto-Indo-European name of the bear is *h₂ŕ̥tḱos, whence Sanskrit r̥kṣa, Avestan arša, Greek ἄρκτος (arktos), Latin ursus, Welsh arth (whence perhaps "Arthur"), Albanian ari, Armenian arj. Also compared is Hittite ḫartagga-, the name of a monster or predator.^[2] In the binomial name of the brown bear, Ursus arctos, Linné simply combined the Latin and Greek names.

The Proto-Indo-European word for bear, *h₂ŕ̥tḱos seems to have been subject to taboo deformation or replacement in some languages (as was the word for wolf, wlk^wos), resulting in the use of numerous unrelated words with meanings like "brown one" (English bruin) and "honey-eater" (Slavic medved), Thus some Indo-European language groups do not share the same PIE root. The theory of the bear taboo is taught to almost all beginning students of Indo-European and historical linguistics; the putative original PIE word for bear is itself descriptive, because a cognate word in Sanskrit is rakṣas, meaning "harm, injury".

Evolutionary history

The family Ursidae is one of nine families in the suborder Caniformia, or "doglike" carnivores, within the order Carnivora. Bears' closest living relatives are the pinnipeds and musteloids.

The following synapomorphic (derived) traits set bears apart from related families:

• presence of an alisphenoid canal
• paroccipital processes that are large and not fused to the auditory bullae
• auditory bullae are not enlarged
• lacrimal bone is vestigial
• cheek teeth are bunodont and hence indicative of a broad, hypocarnivorous (non-strictly meat-eating) diet (although hypercarnivorous (strictly meat-eating) taxa are known from the fossil record)
• carnassials are flattened

Additionally, members of this family possess posteriorly oriented M2 postprotocrista molars, elongated m2 molars, and a reduction of the premolars.

Modern bears comprise eight species in three subfamilies: Ailuropodinae (monotypic with the giant panda), Tremarctinae (monotypic with the Spectacled Bear), and Ursinae (containing six species divided into one to three genera, depending upon authority).

Fossil bears

The earliest members of Ursidae belong to the extinct subfamily Amphicynodontinae, including Parictis (late Eocene to early middle Miocene, 38-18 million years (Ma) ago) and the slightly younger Allocyon (early Oligocene, 34-30 Ma), both from North America. These animals looked very different from today's bears, being small and raccoon-like in overall appearance, and a diet perhaps more similar to that of a badger. Parictis does not appear in Eurasia and Africa until the Miocene. It is unclear whether late Eocene ursids were also present in Eurasia, although faunal exchange across the Bering land bridge may have been possible during a major sea level low stand as early as the late Eocene (~37 Ma) and continuing into the early Oligocene. European genera morphologically very similar to Allocyon, and also the much younger American Kolponomos (~18 Ma), are known from the Oligocene, including Amphicticeps and Amphicynodon.

The raccoon-sized, dog-like Cephalogale is the oldest-known member of the subfamily Hemicyoninae which first appeared during the middle Oligocene in Eurasia ~30 Ma ago. The subfamily also includes the younger genera Phoberocyon (~20-15 Ma), and Plithocyon (~15-7 Ma).A Cephalogale-like species gave rise to the genus Ursavus during the early Oligocene (30-28 Ma); this genus proliferated into many species in Asia and is ancestral to all living bears. Species of Ursavus subsequently entered North America together with Amphicynodon and Cephalogale during the early Miocene (21-18 Ma).Members of living lineages of bears diverged from Ursavus ~20 Ma ago, likely via the species Ursavus elmensis. Based on genetic and morphological data, the subfamily Ailuropodinae (pandas) was the first to diverge from other living bears ~19 Ma ago, although no fossils of this group have been found pre-dating about 5 Ma.

The New World short-faced bears (Tremarctinae) differentiated from Ursinae following a dispersal event into North America during the mid Miocene (~13 Ma).^[10] They invaded South America (~1 Ma) following formation of the Isthmus of Panama.^[11] Their earliest fossil representative is Plionarctos in North America (~10-2 Ma). This genus is probably the direct ancestor to the North American short-faced bears (genus Arctodus), the South American short-faced bears (Pararctotherium and Arctotherium), and the spectacled bears, Tremarctos, represented by both an extinct North American species (T. floridanus), and the lone surviving representative of the Tremarctinae, the South American spectacled bear (T. ornatus).

The subfamily Ursinae experienced a dramatic proliferation of taxa ~5.3-4.5 Ma ago coincident with major environmental changes, with the first members of the genus Ursus also appearing around this time.^[10] The sloth bear is a modern survivor of one of the earliest lineages to diverge during this radiation event (~5.3 Ma); it took on its peculiar morphology related to its diet on termites and ants no later than by the early Pleistocene. By 3-4 Ma ago, the species Ursus minimus appears in the fossil record of Europe, which apart from size is nearly identical to today's Asiatic black bear. It is likely ancestral to all bears within Ursinae, perhaps aside from the sloth bear. Two lineages evolved from U. minimus, the black bears (including the sun bear, the Asiatic black bear, and the American black bear), and the brown bears. Modern brown bears evolved from U. minimus via Ursus etruscus, which itself is ancestral to both the extinct Pleistocene cave bear and the ancestor of today's brown and polar bears. Species of Ursinae have migrated repeatedly into N. America from Eurasia as early as 4 Ma ago during the early Pliocene. The fossil record of bears is exceptionally good. Direct ancestor-descendent relationships between individual species are often fairly well-established, with sufficient intermediate forms known to make the precise cut-off between an ancestral and its daughter species subjective. Other extinct bear genera include Agriarctos, Indarctos, and Agriotherium (sometimes placed within hemicyonids).