Laurasiatheria

Laurasiatheria is 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 (aka 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
 * Cetartiodactyla (unranked) containing the orders:
 * Cetacea: whales, dolphins and porpoises
 * Artiodactyla: even-toed ungulates including camels, pigs, ruminants (giraffes, deer, antelopes, cattle, sheep, goats, etc.) and hippopotamuses; now recognized to be paraphyletic.
 * Ferae (unranked) containing the orders:
 * Pholidota: pangolins, aka 'scaly anteaters' (Africa, South Asia)
 * Carnivora: cats, dogs, bears, seals, and others (cosmopolitan)

There is still uncertainty regarding the phylogenetic tree for extant Laurasiatherians, primarily due to disagreement about the placement of Chiroptera and Perissodactyla. Chiroptera has sometimes been placed by studies into a clade with Eulipotyphla, while the Pegasoferae proposal would unite it with Perissodactyla and Ferae. The most 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" and concluded that "Pegasoferae [...] does not appear to be a natural group." The exact position of Perissodactyla remains less certain however, 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. find better (but not full) support for the latter.

Laurasiatheria is also posited to include several extinct orders and superorders:


 * Meridiungulata
 * Condylarthra
 * Dinocerata
 * Mesonychia
 * Cimolesta
 * Creodonta