/////////////////EVOLUTIONS-BEAR
/////////////////Evolutionary relationships
Fossil of Cave bear (Ursus spelaeus)
The Ursidae family belongs to the order Carnivora and is one of nine families in the suborder Caniformia, or "doglike" carnivorans. Bears' closest living relatives are the pinnipeds, a clade of three families: Odobenidae (the walrus), Otariidae (fur seals and sea lions), and Phocidae (true or earless seals). 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).
The origins of Ursidae can be traced back to the very small and graceful Parictis that had a skull only 7 cm (3 in) long. Parictis first occur in North America in the Late Eocene (ca. 38 million years ago), but this genus did not appear in Eurasia and Africa until the Miocene.[2] The raccoon-sized, dog-like Cephalogale, however, is widely regarded as the most primitive ursid and is ideally suited as a representative basal taxon for the family. Cephalogale first appeared during the middle Oligocene and early Miocene (approximately 20–30 million years ago) in Europe. Cephalogale gave rise to a lineage of early bears of the genus Ursavus. This genus radiated in Asia and ultimately gave rise to the first true bears (genus Ursus) in Europe, 5 million years ago. Even among its primitive species, such as C. minor, it exhibits typical ursid synapomorphic dentition such as posteriorly oriented M2 postprotocrista molars, elongated m2 molars, and a reduction of the premolars. Living members of the ursids are morphologically well defined by their hypocarnivorous (non-strictly meat-eating) dentitions, but fossil ursids include hypercarnivorous (strictly meat-eating) taxa, although they never achieved the extreme hypercarnivory seen in mustelids. Cephalogale was a mesocarnivore (intermediate meat-eater).[3] Other extinct bear genera include Arctodus, Agriarctos, Plionarctos and Indarctos.
It is uncertain whether ursids were in Asia during the late Eocene, although there is some suggestion that a limited immigration from Asia may have produced Parictis in North America due to the major sea level lowstand at ca. 37 Ma, but no Parictis fossils have yet to be found in East Asia. Ursids did, however, become very diversified in Asia later during the Oligocene. Four genera representing two subfamilies (Amphicynodontinae and Hemicyoninae) have been discovered in the Oligocene of Asia: Amphicticeps, Amphicynodon, Pachycynodon, and Cephalogale. Amphicticeps is endemic from Asia and the other three genera are common to both Asia and Europe. This indicates migration of ursids between Asia and Europe during the Oligocene and migration of several taxa from Asia to North America likely occurred later during the late Oligocene or early Miocene. Although Amphicticeps is morphologically closely related to Allocyon, and also to Kolponomos of North America, no single genus of the Ursidae from this time period is known to be common to both Eurasia and North America. Cephalogale, however, do appear in North America in the early Miocene. It is interesting to note that rodents, such as Haplomys and Pseudotheridomys (late Oligocene) and Plesiosminthus and Palaeocastor (early Miocene), are common to both Asia and North America and this indicates that faunal exchange did occur between Asia and North America during the late Oligocene to early Miocene. Ursid migration from Asia to North America would therefore have also been very likely to occur during this time.[4] In the late Neogene three major carnivoran migrations that definitely included ursids are recognized between Eurasia and North America. The first (probably 21–18 Ma) was waves of intermittent dispersals including Amphicynodon, Cephalogale and Ursavus. The second migration occurred about 7–8 Ma and included Agriotherium – this was unusual among ursoids in that it also colonised sub-Saharan Africa. The third wave took place in the early Pliocene 4 Ma, consisting of Ursus.[5]
The giant panda's taxonomy has long been debated. Its original classification by Armand David in 1869 was within the bear genus Ursus, but in 1870 it was reclassified by Alphonse Milne-Edwards to the raccoon family.[6] In recent studies, the majority of DNA analyses suggest that the giant panda has a much closer relationship to other bears and should be considered a member of the family Ursidae.[7] The status of the red panda remains uncertain, but many experts, including Wilson and Reeder, classify it as a member of the bear family. Others place it with the raccoons in Procyonidae or in its own family, the Ailuridae. Multiple similarities between the two pandas, including the presence of false thumbs, are thought to represent convergent evolution for feeding primarily on bamboo.
There is also evidence that, unlike their neighbors elsewhere, the brown bears of Alaska's ABC islands are more closely related to polar bears than they are to other brown bears in the world. Researchers Gerald Shields and Sandra Talbot of the University of Alaska Fairbanks Institute of Arctic Biology studied the DNA of several samples of the species and found that their DNA is different from that of other brown bears. The researchers discovered that their DNA was unique compared to brown bears anywhere else in the world. The discovery has shown that while all other brown bears share a brown bear as their closest relative, those of Alaska's ABC Islands differ and share their closest relation with the polar bear.[8] There is also supposed to be a very rare large bear in China called the blue bear, which presumably is a type of black bear. This animal has never been photographed.
Koalas are often referred to as bears due to their appearance; they are not bears, however, but marsupials.
Classification
Brown Bear Ursus arctos, at the Moscow Zoo
Asiatic Black Bear Ursus thibetanus, at the Wrocław Zoo, Poland
Sun Bear Helarctos malayanus, at the Columbus Zoo
Giant Panda Ailuropoda melanoleuca, "Tian Tian"
Family Ursidae
Subfamily Ailuropodinae
Giant Panda, Ailuropoda melanoleuca
Dwarf Panda, Ailuropoda minor†
Subfamily Tremarctinae
Spectacled Bear, Tremarctos ornatus
Florida Cave Bear, Tremarctos floridanus†
Giant Short-faced Bear, Arctodus simus†
Unnamed short-faced bear species, Arctodus pristinus†
Brazilian Short-faced Bear, Arctotherium brasilense†
Argentine Short-faced Bear, Arctotherium latidens†
Subfamily Ursinae
Brown Bear, Ursus (Ursus) arctos
Subspecies Syrian (Brown) Bear Ursus arctos syriacus
Subspecies Grizzly Bear, Ursus arctos horribilis
Subspecies Kodiak Bear, Ursus arctos middendorffi
Subspecies Himalayan Brown Bear and Himalayan Red Bear, Ursus arctos isabellinus
Subspecies Himalayan Blue Bear, Ursus arctos pruinosus
Subspecies Bergman's Bear, Ursus arctos piscator†?
Subspecies Eurasian Brown Bear Ursus arctos arctos
Gobi bear, Ursus arctos gobiensis (very rare)
Atlas Bear, Ursus arctos crowtheri†
American Black Bear, Ursus (Ursus) americanus
Subspecies Cinnamon Bear, Ursus americanus cinnamomum
Subspecies Kermode Bear, Ursus americanus kermodei
Polar Bear, Ursus maritimus
Asiatic Black Bear, Ursus thibetanus
Formosan Black Bear, Ursus thibetanus formosanus
Ursus thibetanus gedrosianus
Ursus thibetanus japonicus
Ursus thibetanus laniger
Ursus thibetanus mupinensis
Ursus thibetanus thibetanus
Ursus thibetanus ussuricus
Sloth Bear, Melursus ursinus
Subspecies Sri Lankan Sloth Bear Melursus ursinus inornatus
Subspecies Indian Sloth Bear Melursus ursinus ursinus
Sun Bear, Helarctos malayanus
Subspecies Borneo Sun Bear Helarctos malayanus euryspilus
Auvergne Bear, Ursus minimus†
Etruscan Bear, Ursus etruscus†
European Cave Bear, Ursus spelaeus†
MacFarlane's Bear, Ursus (Vetularctos) inopinatus (cryptid; if an authentic species, extinct)
Deninger's bear, Ursus deningeri†
The genera Melursus and Helarctos are sometimes also included in Ursus. The Asiatic black bear and the polar bear used to be placed in their own genera, Selenarctos and Thalarctos which are now placed at subgenus rank.
A number of hybrids have been bred between American black, brown, and polar bears (see Ursid hybrids).
GROLAR BEAR
////////////////////
No comments:
Post a Comment