Laurasiatheria is a clade of placental mammals that originated on the northern supercontinent of Laurasia 99 million years ago. The clade includes shrews, even-toed ungulates, whales, bats, odd-toed ungulates, pangolins, and carnivorans, among others.
Temporal range: Late Cretaceous - Recent
|Clockwise from the upper left: giraffe, golden crown fruit bat, lion, hedgehog|
Waddell et al., 1999
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 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.
A 2013 study by Tsagkogeorga, et al. suggests that the carnivores, cetaceans, chiroptera, and ungulates form an ancient clade. This is supported by a study by Morgan, et al. (2013) that suggests that Eulipotyphla are the earliest diverging clade within the Laurasiatheria.
|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.
The Archonta are a group of mammals, considered a superorder in some classifications, which consists of the following orders:
Plesiadapiformes (extinct—primate-like archontans)
Dermoptera (colugos)While bats were traditionally included in Archonta, recent genetic analysis has suggested that bats actually belong in Laurasiatheria. A revised category, Euarchonta, excluding bats, has been proposed.It has been suggested that this taxon may have arisen in the Early Cretaceous (more than one hundred million years ago) and so there may be other explanatory models for mammalian evolution beside an explosive radiation from a single surviving lineage following the Cretaceous-Paleogene extinction of the Mesozoic megafauna, such as a series of prior radiations related to the breakup of Gondwana and Laurasia allowing for more survivors.Astrapotheria
Astrapotheria is an extinct order of South American and Antarctic hoofed mammals that existed from the Late Paleocene to the Middle Miocene, 59 to 11.8 million years ago. Astrapotheres were large and rhinoceros-like animals and are certainly one of the most bizarre orders of mammals with an enigmatic evolutionary history.This taxonomy of this order is not clear, but it may belong to Meridiungulata (along with Notoungulata, Litopterna, Pyrotheria and Xenungulata). In turn, Meridungulata is believed to belong to the extant superorder Laurasiatheria. Some scientists have regarded the astrapotheres (and sometimes the Meridiungulata all together) as members of the clade Atlantogenata. However, recent collogen and mitonchodrial DNA sequence data places at least the notoungulates and litopterns firmly within Laurasiatheria, as a sister group to the perissodactyls.An example of this order is Astrapotherium magnum. When alive, Astrapotherium might have resembled a mastodon, but was only three meters (ten feet) long.Boreoeutheria
Boreoeutheria (synonymous with Boreotheria) (from Greek Βορέας, Boreas "the greek god of north wind", εὐ-, eu- "good, right" and θηρίον, thēríon "beast" hence "northern true beasts") is a clade (magnorder) of placental mammals which is composed of the sister taxa Laurasiatheria (most hoofed mammals, most pawed carnivores, and several other groups) and Euarchontoglires (Supraprimates). It is now well supported by DNA sequence analyses, as well as retrotransposon presence or absence data. Placental mammals outside of this clade are the clades Xenarthra (sloths and their close relatives) and Afrotheria (elephants and their close relatives).
The earliest known fossils belonging to this group date to about 65 million years ago, shortly after the K-Pg extinction event, though molecular data suggest they may have originated earlier, during the Cretaceous period.With a few exceptions male animals in the clade have a scrotum which serves the function of cooling the testicles to improve the production of sperm. The sub-clade Scrotifera was named after this feature.Dinocerata
Dinocerata ("terrible horned") is an extinct order of plant-eating, rhinoceros-like hoofed creatures famous for their paired horns and tusk-like canine teeth. The earliest dinoceratan, Prodinoceras, appeared in Asia during the Paleocene, but nearly all later types are from North America (dinoceratans must have crossed the Bering land bridge, which may have been exposed during Paleocene-Eocene times). Dinoceratans lived alongside another group of large Eocene plant-eaters, the brontotheres. The most famous dinoceratan is Uintatherium.Equidae
Equidae (sometimes known as the horse family) is the taxonomic family of horses and related animals, including the extant horses, donkeys, and zebras, and many other species known only from fossils. All extant species are in the genus Equus. Equidae belongs to the order Perissodactyla, which includes the extant tapirs and rhinoceros, and several extinct families.
The term equid refers to any member of this family, including any equine.Euarchontoglires
Euarchontoglires (synonymous with Supraprimates) 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.Eulipotyphla
Eulipotyphla ("truly fat and blind") is an order of mammals suggested by molecular methods of phylogenetic reconstruction, and includes the laurasiatherian members of the now-invalid polyphyletic order Lipotyphla, but not the afrotherian members (tenrecs and golden moles, now in their own order Afrosoricida). Lipotyphla in turn had been derived by removing a number of groups from Insectivora, the previously used wastebasket taxon.
Eulipotyphla comprises the hedgehogs and gymnures (family Erinaceidae, formerly also the order Erinaceomorpha), solenodons (family Solenodontidae), the desmans, moles, and shrew-like moles (family Talpidae) and true shrews (family Soricidae). True shrews, talpids and solenodons were formerly grouped in Soricomorpha; however, Soricomorpha has been found to be paraphyletic, since erinaceids are the sister group of shrews.Exafroplacentalia
Exafroplacentalia or Notolegia is a clade of placental mammals proposed in 2001 on the basis of molecular research.Exafroplacentalia places Xenarthra as a sister group to the Boreoeutheria (comprising Laurasiatheria and Euarchontoglires), thus making Afrotheria a primitive group of placental mammals (the group name roughly means "those which are not African placentals").Ferungulata
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.
The traditional Ferungulata was established by George Gaylord Simpson in 1945. It grouped together the extant orders Carnivora, Perissodactyla and Artiodactyla with the Tubulidentata and the superorder Paenungulata, as well as a number of orders known only from fossils. Although Simpson placed whales (Cetacea) in a separate cohort, recent evidence linking them to Artiodactyla would mean that they belong here as well.
Simpson established the grouping on the basis of morphological criteria, but this traditional understanding of Ferungulata has been challenged by a more recent classification, relying upon genetic criteria. These studies separated his ungulate orders into two distinct placental groups, within Afrotheria and Laurasiatheria, respectively. The 'true' ungulates, Perissodactyla and Artiodactyla, along with the whales, are included in the revised group, along with the Carnivora, and with the addition of pangolins (Pholidota), but the Tubulidentata and paenungulates are excluded. To reflect this difference, the revised clade is usually referred to as Fereuungulata. The Fereuungulata is a sister group to the Chiroptera (bats) and together they make up Scrotifera.Insectivora
The order Insectivora (from Latin insectum "insect" and vorare "to eat") is a now-abandoned biological grouping within the class of mammals. Some species have now been moved out, leaving the remaining ones in the order Eulipotyphla, within the larger clade Laurasiatheria, which makes up one of the most basic clades of placental mammals.Mammal classification
Mammalia is a class of animal within the Phylum Chordata. Mammal classification has been through several iterations since Carl Linnaeus initially defined the class. No classification system is universally accepted; McKenna & Bell (1997) and Wilson & Reader (2005) provide useful recent compendiums. Many earlier ideas from Linnaeus et al. have been completely abandoned by modern taxonomists, among these are the idea that bats are related to birds or that humans represent a group outside of other living things. Competing ideas about the relationships of mammal orders do persist and are currently in development. Most significantly in recent years, cladistic thinking has led to an effort to ensure that all taxonomic designations represent monophyletic groups. The field has also seen a recent surge in interest and modification due to the results of molecular phylogenetics.
George Gaylord Simpson's classic "Principles of Classification and a Classification of Mammals" (Simpson, 1945) taxonomy text laid out a systematics of mammal origins and relationships that was universally taught until the end of the 20th century.
Since Simpson's 1945 classification, the paleontological record has been recalibrated, and the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself, partly through the new concept of cladistics. Though field work gradually made Simpson's classification outdated, it remained the closest thing to an official classification of mammals. See list of placental mammals and list of monotremes and marsupials for more detailed information on mammal genera and species.Mormoopidae
The family Mormoopidae contains bats known generally as mustached bats, ghost-faced bats, and naked-backed bats. They are found in the Americas from the Southwestern United States to Southeastern Brazil.
They are distinguished by the presence of a leaf-like projection from their lips, instead of the nose-leaf found in many other bat species. In some species, the wing membranes join over the animal's back, making it appear hairless. The tail projects only a short distance beyond the membrane that stretches between the hind legs. They are brownish in colour, with short, dense fur. Their dental formula is:
Mormoopid bats roost in caves and tunnels in huge colonies that may include hundreds of thousands of members, producing enough guano to allow commercial mining. They do not hibernate as some other bats do since they live in the tropics. They feed on insects found close to, or on, bodies of water.Natalidae
The family Natalidae, or funnel-eared bats, are found from Mexico to Brazil and the Caribbean islands. The family has three genera, Chilonatalus, Natalus and Nyctiellus. They are slender bats with unusually long tails and, as their name suggests, funnel-shaped ears. They are small, at only 3.5 to 5.5 cm (1.4 to 2.2 in) in length, with brown, grey, or reddish fur. Like many other bats, they are insectivorous, and roost in caves.Placentalia
Placentalia ("Placentals") is one of the three extant subdivisions of the class of animals Mammalia; the other two are Monotremata and Marsupialia. The Placentals are partly distinguishable from other mammals in that the fetus is carried in the uterus of its mother to a relatively late stage of development. It is somewhat of a misnomer since marsupials also nourish their fetuses via a placenta.Pyrotheria
Pyrotheria is an order of extinct meridiungulate mammals. These mastodon-like ungulates include the genera Baguatherium, Carolozittelia, Colombitherium, Gryphodon, Propyrotherium, Proticia, and Pyrotherium.They had the appearance of large, digitigrade, tapir-like mammals with relatively short, slender limbs and five-toed feet with broad, flat phalanges. Their fossils are restricted to Paleocene through Oligocene deposits of Brazil, Peru and Argentina.
Some experts place the clade Xenungulata (which contains several genera, including Carodnia) within Pyrotheria, even when dentition, although bilofodont in both orders, is very different. For most scholars, the two orders remain separated. The dentition is complete with strong, procumbent, chisel-shaped incisors, strong sharp-pointed canines, and low-crowned cheek teeth with bilophodont molars. The affinities of the Xenungulata remain uncertain. Affinities with the Dinocerata are strongly supported by the dental characteristics. Initial study of the structure of the tarsus suggested that the xenungulates had a common ancestry with typical pyrotheres, such as Pyrotherium, but a more recent examination of the tarsus of Pyrotherium failed to support this, instead showing some traits shared by Pyrotherium and the Embrithopoda. It remains to be seen which of these views will turn out to be right. This means that the Pyrotheria could be members of no less than three major cladistic branches of placential mammals: Meridiungulata (if xenungulates are the closest relatives), Laurasiatheria (if dinoceratans are the closest relatives) and Afrotheria (if embrithopods are the closest relatives).Scrotifera
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.
Extant mammal orders