|Clade:|| Laurasiatheria |
Waddell et al., 1999
Laurasiatheria is a clade of placental mammals that includes hedgehogs, even-toed ungulates, whales, bats, odd-toed ungulates, pangolins, and carnivorans, among others.The clade originated on the northern supercontinent of Laurasia. Its last common ancestor is supposed to have diversified ca. 76 to 91 million years ago.
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 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:
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 2011 study 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." A 2012 study supports the previous conclusions using a large genomic dataset, and places 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', yet some authors found better (but not full) support for the latter, while others found Perissodactyla to be sister to Carnivora.
Two 2013 studies retrieve that chiropterans, carnivores, and euungulates form a clade, therefore involving that Eulipotyphla might be the sister group to all other Laurasiatheria taxa.
|Order-level cladogram of the Laurasiatheria.|
|The cladogram has been reconstructed from mitochondrial and nuclear DNA and protein characters.|
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.
Carnivora is an order of placental mammals that have specialized in primarily eating flesh. Its members are formally referred to as carnivorans, though some species are omnivorous, such as raccoons and bears, and quite a few species such as pandas are specialized herbivores. The word 'carnivore' is derived from Latin carō "flesh" and vorāre "to devour", it refers to any meat-eating organism. The order Carnivora is the fifth largest order of mammals and one of the more successful members of the group; it comprises at least 279 species living on every major landmass and in a variety of habitats, ranging the cold polar regions to the hyper-arid region of the Sahara Desert to the open seas. They come in a huge array of different body plans in contrasting shapes and sizes. The smallest carnivoran is the least weasel with a body length of about 11 cm (4.3 in) and a weight of about 25 g (0.88 oz). The largest is the southern elephant seal, with adult males weighing up to 5,000 kg (11,000 lb) and measuring up to 6.7 m (22 ft). All species of carnivorans are descended from a group of mammals which were related to today's pangolins, having appeared in North America 6 million years after the Cretaceous–Paleogene extinction event. These early ancestors of carnivorans would have resembled small weasel or genet-like mammals, occupying a nocturnal shift on the forest floor or in the trees, as other groups of mammals like the mesonychians and creodonts were occupying the top faunivorous niche. However, by the time Miocene epoch appeared, most if not all of the major lineages and families of carnivorans had diversified and took over this niche.
Odd-toed ungulates, mammals which constitute the taxonomic order Perissodactyla, are hoofed animals—ungulates—which bear most of their weight on one of the five toes: the third toe. The non-weight-bearing toes are either present, absent, vestigial, or positioned posteriorly. By contrast, the even-toed ungulates bear most of their weight equally on two of the five toes: their third and fourth toes. Another difference between the two is that odd-toed ungulates digest plant cellulose in their intestines rather than in one or more stomach chambers as the even-toed ungulates do.
Ungulates are members of a diverse clade of primarily large mammals with hooves. These include odd-toed ungulates such as horses, rhinoceroses and tapirs, and even-toed ungulates such as cattle, pigs, giraffes, camels, sheep, deer, and hippopotamuses. Cetaceans are also even-toed ungulates although they do not have hooves. Most terrestrial ungulates use the tips of their toes, usually hoofed body weight while moving.
Placentalia is one of the three extant subdivisions of the class of animals Mammalia; the other two are Monotremata and Marsupialia. The placentals are partly distinguished from other mammals in that the fetus is carried in the uterus of its mother to a relatively late stage of development. The name is something of a misnomer considering that marsupials also nourish their fetuses via a placenta, though for a relatively briefer period, giving birth to less developed young who are then kept for a period in the mother's pouch.
Eutheria is one of two mammalian clades with extant members that diverged in the Early Cretaceous or perhaps the Late Jurassic. All placental mammals indigenous to Europe, Africa, Asia, the Americas, Australia, and Antarctica are eutherians. Extant eutherians, their last common ancestor, and all extinct descendants of that ancestor are members of Placentalia.
Afrotheria is a clade of mammals, the living members of which belong to groups that are either currently living in Africa or of African origin: golden moles, elephant shrews, tenrecs, aardvarks, hyraxes, elephants, sea cows, and several extinct clades. Most groups of afrotheres share little or no superficial resemblance, and their similarities have only become known in recent times because of genetics and molecular studies. Many afrothere groups are found mostly or exclusively in Africa, reflecting the fact that Africa was an island continent from the early Cenozoic until around 25 million years ago, when the Tethys Sea shrank.
Euarchontoglires is a clade and a superorder of mammals, the living members of which belong to one of the five following groups: rodents, lagomorphs, treeshrews, colugos and primates.
The Euarchonta are a proposed grandorder of mammals containing four orders: the Scandentia or treeshrews, the Dermoptera or colugos, the extinct Plesiadapiformes, and the Primates.
Condylarthra is an informal group – previously considered an order – of extinct placental mammals, known primarily from the Paleocene and Eocene epochs. They are considered early, primitive ungulates. It is now largely considered to be a wastebasket taxon, having served as a dumping ground for classifying ungulates which had not been clearly established as part of either Perissodactyla or Cetartiodactyla, being composed thus of several unrelated lineages.
Ferae is a clade of mammals, consisting of the orders Carnivora and Pholidota. An alternate name, Ostentoria, has also been proposed for a grouping of the Carnivora and Pholidota. The last common ancestor of extant Ferae is supposed to have diversified ca. 78.9 million years ago. Several extinct orders, relatives of the Pholidota, such as Creodonts, are members of Ferae as well.
Atlantogenata is a proposed clade of mammals containing the cohorts or superorders Xenarthra and Afrotheria. These groups originated and radiated in the South American and African continents, respectively, presumably in the Cretaceous. Together with Boreoeutheria, they make up Eutheria. The monophyly of this grouping was supported by some genetic evidence.
Cimolesta is an extinct order of non-placental eutherian mammals. Cimolestans had a wide variety of body shapes, dentition and lifestyles, though the majority of them were small to medium-sized general mammals that bore superficial resemblances to rodents, weasels or opossums.
Zooamata is a proposal for a clade of mammals uniting the Ferae with the Perissodactyla. The name is constructed from Greek and Latin to mean "animal friends", a reference to the inclusion of cats, dogs, and horses.
Boreoeutheria is a clade (magnorder) of placental mammals which is composed of the sister taxa Laurasiatheria and Euarchontoglires (Supraprimates). It is now well supported by DNA sequence analyses, as well as data regarding retrotransposon presence or absence. Placental mammals outside of this clade are the clades Xenarthra and Afrotheria.
Ferungulata or Fereuungulata is a clade of placental mammals that groups together various carnivorans and ungulates. It has existed in two guises, a traditional one based on morphological analysis and a revised one taking into account more recent molecular analyses.
Pegasoferae is a proposed clade of mammals based on genomic research in molecular systematics by Nishihara, Hasegawa and Okada (2006).
Whippomorpha is the clade containing the Cetaceans and their closest living relatives, the hippopotamuses, named by Waddell et al. (1999). It is defined as a crown group, including all species that are descendants of the most recent common ancestor of Hippopotamus amphibius and Tursiops truncatus. This would be a subgrouping of the Cetartiodactyla. The genetic evidence is strong that the cetaceans arose from within the Artiodactyla, thus making the even-toed ungulate grouping a paraphyletic one. How recently whales and hippos share a common ancestor is unclear.
Artiofabula is a clade made up of the Suina and the Cetruminantia. The clade was found in molecular phylogenetic analyses and contradicted traditional relationships based on morphological analyses.
Scrotifera is a clade of placental mammals that comprises the following orders and their common ancestors: Chiroptera, Carnivora, Pholidota, Perissodactyla and Cetartiodactyla, with the latter including the traditional orders Artiodactyla and Cetacea. Scrotifera is the sister group to the Eulipotyphla and together they make up the Laurasiatheria. The last common ancestor of Scrotifera is supposed to have diversified ca. 73.1 to 85.5 million years ago.
Pholidotamorpha is a clade of mammals that includes the orders Palaeanodonta and Pholidota. In the past both orders were formerly classified with various other orders of ant-eating mammals, most notably Xenarthra, which includes the true anteaters, sloths, and the armadillos which pangolins superficially resemble. Newer genetic evidence, however, indicates their closest living relatives are the Carnivora with which they form the clade Ferae. Some palaeontologists, placing Ernanodonta in a separate suborder of Cimolesta near Pholidota, have classified the pangolins in the order Cimolesta, together with several extinct groups indicated (†) below, though this idea has fallen out of favor since it was determined that cimolestids were not placental mammals. A 2015 study has supported close affinities between pangolins and the extinct group Creodonta, as well as many former cimolestans.