Bears are carnivoran mammals of the family Ursidae. They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats throughout the Northern Hemisphere and partially in the Southern Hemisphere. Bears are found on the continents of North America, South America, Europe, and Asia. Common characteristics of modern bears include large bodies with stocky legs, long snouts, small rounded ears, shaggy hair, plantigrade paws with five nonretractile claws, and short tails.
While the polar bear is mostly carnivorous, and the giant panda feeds almost entirely on bamboo, the remaining six species are omnivorous with varied diets. With the exception of courting individuals and mothers with their young, bears are typically solitary animals - learn more. They may be diurnal or nocturnal and have an excellent sense of smell. Despite their heavy build and awkward gait, they are adept runners, climbers, and swimmers.
Etymology
The English word "bear" comes from Old English bera and belongs to a family of names for the bear in Germanic languages, such as Swedish björn, also used as a first name. This form is conventionally said to be related to a Proto-Indo-European word for "brown", so that "bear" would mean "the brown one".[1][2] However, Ringe notes that while this etymology is semantically plausible, a word meaning "brown" of this form cannot be found in Proto-Indo-European.
Taxonomy
The family Ursidae is one of the nine families in the suborder Caniformia, or "doglike" carnivorans, within the order Carnivora. Bears' closest living relatives are the pinnipeds, canids, and musteloids. 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 on the authority). Nuclear chromosome analysis show that the karyotype of the six ursine bears is nearly identical, with each having 74 chromosomes, whereas the giant panda has 42 chromosomes and the spectacled bear 52.
Evolution
The earliest members of Ursidae belong to the extinct subfamily Amphicynodontinae, including Parictis (late Eocene to early middle Miocene, 38–18 Mya) and the slightly younger Allocyon (early Oligocene, 34–30 Mya), both from North America. These animals looked very different from today's bears, being small and raccoon-like in overall appearance, with diets perhaps more similar to that of a badger. Parictis does not appear in Eurasia and Africa until the Miocene.[14] 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 (about 37 Mya) and continuing into the early Oligocene. European genera morphologically very similar to Allocyon, and to the much younger American Kolponomos (about 18 Mya), 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 about 30 Mya.[15] The subfamily includes the younger genera Phoberocyon (20–15 Mya), and Plithocyon (15–7 Mya). A Cephalogale-like species gave rise to the genus Ursavus during the early Oligocene (30–28 Mya); 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 Mya). Members of the living lineages of bears diverged from Ursavus between 15 and 20 Mya,[24][25] likely via the species Ursavus elmensis. Based on genetic and morphological data, the Ailuropodinae (pandas) were the first to diverge from other living bears about 19 Mya, although no fossils of this group have been found before about 5 Mya.
Size
Polar bear (left) and sun bear, the largest and smallest species respectively, on average The bear family includes the most massive extant terrestrial members of the order Carnivora.[a] The polar bear is considered to be the largest extant species,[39] with adult males weighing 350–700 kg (772–1,543 lb) and measuring 2.4–3 metres (7 ft 10 in–9 ft 10 in) in total length.[40] The smallest species is the sun bear, which ranges 25–65 kg (55–143 lb) in weight and 100–140 cm (39–55 in) in length.[41] Prehistoric North and South American short-faced bears were the largest species known to have lived. The latter estimated to have weighed 1,600 kg (3,500 lb) and stood 3.4 m (11 ft) tall.[42][43] Body weight varies throughout the year in bears of temperate and arctic climates, as they build up fat reserves in the summer and autumn and lose weight during the winter.