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Laurasiatheria is the scientific name of a large group of placental mammals believed to have originated on the northern supercontinent of Laurasia. It includes shrews, hedgehogs, pangolins, bats, whales, most hoofed mammals, and carnivorans, among others. ==Classification and phylogeny== Laurasiatheria was discovered on the basis of the similar gene sequences shared by the mammals belonging to it; no anatomical features have yet been found that unite the group. Laurasiatheria is a clade usually discussed without a Linnaean rank, but has been assigned the rank of cohort or magnorder, and superorder. The Laurasiatheria clade is based on DNA sequence analyses and retrotransposon presence/absence data. The name comes from the theory that these mammals evolved on the supercontinent of Laurasia, after it split from Gondwana when Pangaea broke up. It is a sister group to Euarchontoglires (or Supraprimates) with which it forms the clade Boreoeutheria. Laurasiatheria includes the following extant taxa: *Eulipotyphla, having subsumed: * *Erinaceomorpha: hedgehogs and gymnures (see Erinaceidae) * *the remaining families of Soricomorpha: moles, shrews, solenodons (cosmopolitan distribution) *Chiroptera: bats (cosmopolitan) *Perissodactyla: odd-toed ungulates including horses, tapirs and rhinoceroses *Artiodactyla: even-toed ungulates including camels, pigs, ruminants (giraffes, deer, antelopes, cattle, sheep, goats, etc.), hippopotamuses and cetaceans * *Cetacea: whales, dolphins, and porpoises *Ferae (unranked) containing the orders: * *Pholidota: pangolins ('scaly anteaters') (Africa, South Asia) * *Carnivora: cats, dogs, bears, seals, and others (cosmopolitan) Uncertainty still exists regarding the phylogenetic tree for extant laurasiatherians, primarily due to disagreement about the placement of Chiroptera and Perissodactyla. Based on morphological grounds, Chiroptera had long been classified in the superorder Archonta (e.g. along with treeshrews and the gliding colugos) until genetic research instead showed their kinship with the other laurasiatherians. The studies conflicted in terms of the exact placement of Chiroptera, however, with it being linked most closely to groups such as Eulipotyphla, Ferae or with Perissodactyla and Ferae in the Pegasoferae proposal. A recent study (Zhou et al., 2011) found that "trees reconstructed () for the 1,608-gene data set fully support () a basal position for Eulipotyphla and a more apical position for Chiroptera" (see cladogram below) and concluded that "Pegasoferae () does () not appear to be a natural group." The most recent study (Nery et al., 2012) supports the conclusions of Zhou et al. using a large genomic dataset, placing Eulipotyphla as a basal order and Chiroptera as sister to Cetartiodactyla, with maximal support for all nodes of their phylogenetic tree. The exact position of Perissodactyla remains less certain, with some studies linking it with Ferae into a proposed clade Zooamata while others unite it with Cetartiodactyla into Euungulata, a clade of 'true ungulates'; Zhou et al. found better (but not full) support for the latter, while Nery et al. found Perissodactyla to be sister to Carnivora. Laurasiatheria has also posited to include several extinct orders and superorders. At least some of these are considered wastebasket taxons, historically lumping together several lineages based on superficial attirbutes and assumed relations to modern mammals. In some cases, these orders have turned out to either be paraphyletic assemblages, or to be composed of mammals now understood not to be laurasiatheres at all. * Meridiungulata (possibly polyphyletic; Liptopterna and Notoungulata are now understood to be stem-perissodactyls, but other clades like Astrapotheria may be unrelated.) * Condylarthra (paraphyletic in relation to true ungulates, possibly outrightly polyphyletic since some forms may be afrotheres or even non-placental eutherians) * Dinocerata (natural clade closely related to perissodactyls and meridiungulates)〔BURGER, Benjamin J., THE SYSTEMATIC POSITION OF THE SABER-TOOTHED AND HORNED GIANTS OF THE EOCENE: THE UINTATHERES (ORDER DINOCERATA), Utah State University Uintah Basin Campus, Vernal, UT, United States of America, 84078 , SVP 2015〕 * Mesonychia (natural clade, though several members, such as ''Andrewsarchus'', are now thought to belong in other groups) * Creodonta (polyphyletic, composed almost entirely of several unrelated clades of laurasiatheres and afrotheres) * Desmostylia (natural clade, historically considered afrotheres but now understood to be stem-perissodactyls) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Laurasiatheria」の詳細全文を読む スポンサード リンク
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