Waddell et al., 1999
Laurasiatheria ("laurasian beasts") is a superorder of placental mammals that groups together order Eulipotyphla and clade Scrotifera. It is a sister group to Euarchontoglires with which it forms the magnorder Boreoeutheria. 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. The Laurasiatheria clade is based on DNA sequence analyses and retrotransposon presence/absence data. The superorder originated on the northern supercontinent of Laurasia, after it split from Gondwana when Pangaea broke up. Its last common ancestor is supposed to have diversified ca. 76 to 90 million years ago.
The name of this superorder comes from the theory that these mammals evolved on the supercontinent of Laurasia. In contrast, extinct primitive mammals called Gondwanatheria existed in the supercontinent of Gondwana.
Uncertainty still exists regarding the phylogenetic tree for extant laurasiatherians, primarily due to disagreement about the placement of orders Chiroptera and Perissodactyla. Based on morphological grounds, bats (order Chiroptera) had long been classified in the superorder Archonta (e.g. along with primates, treeshrews and the gliding colugos) until genetic research instead showed their kinship with the other laurasiatheres. The studies conflicted in terms of the exact placement of Chiroptera, however, with it being linked most closely to groups such as order Eulipotyphla in the clade Insectiphillia. Two 2013 studies retrieve that bats, carnivorans and euungulates form a clade Scrotifera, therefore involving that Eulipotyphla might be a basal group to all other Laurasiatheria taxa.
|Phylogeny within superorder Laurasiatheria|
|The cladogram has been reconstructed from mitochondrial and nuclear DNA and protein characters, as well as the fossil record.|
Laurasiatheria is also posited to include several extinct orders and superorders. At least some of these are considered wastebasket taxa, historically lumping together several lineages based on superficial attributes 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.