Eutheria

Eutheria (/juːˈθɪəriə/; from Greek εὐ-, eu- "good" or "right" and θηρίον, thēríon "beast" hence "true beasts") is one of two mammalian clades with extant members that diverged in the Early Cretaceous or perhaps the Late Jurassic. Except for the North American Virginia opossum, which is a metatherian, all post-Miocene mammals indigenous to Europe, Africa, Asia, and North America north of Mexico are eutherians. Extant eutherians, their last common ancestor, and all extinct descendants of that ancestor are members of Placentalia.

Eutherians are distinguished from noneutherians by various phenotypic traits of the feet, ankles, jaws and teeth. All extant eutherians lack epipubic bones, which are present in all other living mammals (marsupials and monotremes). This allows for expansion of the abdomen during pregnancy.[2]

The oldest-known eutherian species is Juramaia sinensis, dated at 161 million years ago from the Jurassic in China.[3]

Eutheria was named in 1872 by Theodore Gill; in 1880 Thomas Henry Huxley defined it to encompass a more broadly defined group than Placentalia.[4]

Eutheria
Temporal range: Late Jurassic or Early CretaceousHolocene, 161 or 125–0 Ma
Juramaia NT
Juramaia, the oldest known eutherian
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Subclass: Theria
Clade: Eutheria
Gill, 1872
Subgroups

Characteristics

Cambridge Natural History Mammalia Fig 068
The entocuneiform bone

Distinguishing features are:

  • an enlarged malleolus ("little hammer") at the bottom of the tibia, the larger of the two shin bones[5]
  • the joint between the first metatarsal bone and the entocuneiform bone (the outermost of the three cuneiform bones) in the foot is offset farther back than the joint between the second metatarsal and middle cuneiform bones—in metatherians these joints are level with each other[5]
  • various features of jaws and teeth[5]

Evolutionary history

Eutheria contains several extinct genera as well as larger groups, many with complicated taxonomic histories still not fully understood. Members of the Adapisoriculidae, Cimolesta and Leptictida have been previously placed within the out-dated placental group Insectivora, while Zhelestids have been considered primitive ungulates.[6] However, more recent studies have suggested these enigmatic taxa represent stem group eutherians, more basal to Placentalia.[7][8]

The weakly favoured cladogram favours Boreoeuthearia as a basal Eutherian clade as sister to the Atlantogenata.[9][10][11]

Eutheria  
Atlantogenata

Xenarthra

Afrotheria

Boreoeutheria

Laurasiatheria

Euarchontoglires

The fossil eutherian species believed to be the oldest known is Juramaia sinensis, which lived about 160 million years ago.[3] Montanalestes was found in North America, while all other nonplacental eutherian fossils have been found in Asia. The earliest-known placental fossils have also been found in Asia.[5]
Cynodonts

Tritylodontids

Mammaliaformes

Other mammaliaformes

Hadrocodium

Mammals
Australosphenids

Other
Australosphenids

Monotremes

Theria

Metatheria

Eutheria

Simplified, non-systematic, outline of evolution of eutheria from cynodont therapsids.[5]
† = extinct

References

  1. ^ Rook, Deborah L.; Hunter, John P. (April 2013). "Rooting Around the Eutherian Family Tree: the Origin and Relations of the Taeniodonta". Journal of Mammalian Evolution. 21: 75–91. doi:10.1007/s10914-013-9230-9.
  2. ^ Reilly, Stephen M.; White, Thomas D. (2003-01-17). "Hypaxial Motor Patterns and the Function of Epipubic Bones in Primitive Mammals". Science. 299 (5605): 400–402. Bibcode:2003Sci...299..400R. doi:10.1126/science.1074905. ISSN 0036-8075. PMID 12532019.
  3. ^ a b Luo, Z.; C. Yuan; Q. Meng; Q. Ji (2011). "A Jurassic eutherian mammal and divergence of marsupials and placentals". Nature. 476 (7361): 42–45. Bibcode:2011Natur.476..442L. doi:10.1038/nature10291. PMID 21866158.
  4. ^ Eutheria (Placental Mammals) by J David Archibald, San Diego State University, San Diego, California, USA. PDF file from sdsu.edu
  5. ^ a b c d e Ji, Q.; Luo, Z-X.; Yuan, C-X.; Wible, J.R.; Zhang, J-P. & Georgi, J.A. (April 2002). "The earliest known eutherian mammal". Nature. 416 (6883): 816–822. Bibcode:2002Natur.416..816J. doi:10.1038/416816a. PMID 11976675.
  6. ^ Rose, Kenneth D. (2006). The beginning of the age of mammals. Baltimore: Johns Hopkins University Press. ISBN 9780801892219.
  7. ^ Wible, J. R.; Rougier, G. W.; Novacek, M. J.; Asher, R. J. (2007). "Cretaceous eutherians and Laurasian origin for placental mammals near the K/T boundary". Nature. 447 (7147): 1003–1006. Bibcode:2007Natur.447.1003W. doi:10.1038/nature05854. PMID 17581585.
  8. ^ Wible, John R.; Rougier, Guillermo W.; Novacek, Michael J.; Asher, Robert J. (2009). "The Eutherian Mammal Maelestes gobiensis from the Late Cretaceous of Mongolia and the phylogeny of cretaceous eutheria" (PDF). Bulletin of the American Museum of Natural History. 327: 1–123. doi:10.1206/623.1. hdl:2246/6001.
  9. ^ Foley, Nicole M.; Springer, Mark S.; Teeling, Emma C. (2016-07-19). "Mammal madness: is the mammal tree of life not yet resolved?". Phil. Trans. R. Soc. B. 371 (1699): 20150140. doi:10.1098/rstb.2015.0140. PMC 4920340. PMID 27325836.
  10. ^ Tarver, James E.; Reis, Mario dos; Mirarab, Siavash; Moran, Raymond J.; Parker, Sean; O'Reilly, Joseph E.; King, Benjamin L.; O'Connell, Mary J.; Asher, Robert J. (2016-02-01). "The Interrelationships of Placental Mammals and the Limits of Phylogenetic Inference". Genome Biology and Evolution. 8 (2): 330–344. doi:10.1093/gbe/evv261. PMC 4779606. PMID 26733575.
  11. ^ Esselstyn, Jacob A.; Oliveros, Carl H.; Swanson, Mark T.; Faircloth, Brant C. (2017-08-26). "Investigating Difficult Nodes in the Placental Mammal Tree with Expanded Taxon Sampling and Thousands of Ultraconserved Elements". Genome Biology and Evolution. 9 (9): 2308–2321. doi:10.1093/gbe/evx168. PMC 5604124. PMID 28934378.
Afrodon

Afrodon is an extinct genus of eutherians in the family Adapisoriculidae. Its type species is Afrodon chleuhi, known from the late Palaeocene of Morocco. The other known species are Afrodon germanicus from the late Palaeocene of Germany and France, Afrodon tagourtensis from the early Eocene of Morocco, Afrodon ivani from the late Palaeocene of Spain, and Afrodon gheerbranti from the early Paleocene of Belgium. Its range spread from the Cernaysian to the Grauvian in the European land mammal ages.

Arcantiodelphys

Arcantiodelphys is an extinct genus of basal Metatheria which existed in France during the Cenomanian age. It was first named by Romain Vullo, Emmanuel Gheerbrant, Christian de Muizon and Didier Néraudeau in 2009 and the type species is Arcantiodelphys marchandi.

Asioryctitheria

Asioryctitheria ("asian digging beasts") is an extinct order of early eutherians.

Bustylus

Bustylus is an extinct genus of eutherians in the family Adapisoriculidae. It was described by Emmanuel Gheerbrandt and Russell in 1991, and the type species is B. cernaysi, described from the late Paleocene of Cernay, France (from which the species epithet was derived), and possibly also from Germany. Gheerbrandt later redescribed the species Peradectes marandati (Crochet and Sigé, 1983) as a species of Bustylus. A third species, B. folieae, was described from the early Paleocene of Belgium by Eric De Bast, Bernard Sigé and Thierry Smith in 2012. B. folieae was named in honour of Dr. Annelise Folie.

Cladotheria

Cladotheria is a group (legion) of mammals that includes the ancestor of Dryolestoidea, Peramuridae and Zatheria (living therians plus all of its ancestors).

Dryolestes

Dryolestes is an extinct genus of Late Jurassic mammal from the Morrison Formation and the Alcobaça Formation of Portugal.

Present in stratigraphic zones 2, 5, and 6.

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").

Juramaia

Juramaia is an extinct genus of very basal eutherian mammal from the Late Jurassic (Oxfordian stage) deposits of western Liaoning, China; it is a small shrew-like mammal with a body length approximately 70–100 mm, similar in size to the modern De Winton's shrew. Juramaia is known from the holotype BMNH PM1343, an articulated and nearly complete skeleton including incomplete skull preserved with full dentition.

Leptictida

Leptictida (leptos iktis "small/slender weasel") is a possibly invalid extinct order of placental mammals. Their classification is contentious: according to cladistic studies, they may be (distantly) related to Euarchontoglires (rodents, primates and their relatives), although they are more recently regarded as the first branch to split from basal eutherians. One recent large-scale cladistic analysis of eutherian mammals favored lepictidans as close to the placental crown-clade; and several other recent analyses that included data from Cretaceous non-eutherian mammals found Leptictis to belong to the superorder Afrotheria.The most recent phylogenetic studies recover it as actually a paraphyletic assemblage leading to Placentalia.

List of mammals of Samoa

This is a list of the mammal species recorded in Samoa. There are nine mammal species in Samoa, of which one is endangered and two are vulnerable.

Montanalestes

Montanalestes is an extinct mammal known from the Cretaceous in North America.

Nanocuris

Nanocuris is an extinct genus of Deltatheridiidae from Cretaceous of Canada (Saskatchewan) and United States (Wyoming - Lance Formation). Initially was classified in a proper family, Nanocuridae, in clade Eutheria, but a reanalysis of a new specimen reveal a deltharoid affinity of the genus.

Palaeosinopa

Palaeosinopa is an extinct genus of semi-aquatic, non-placental eutherian mammals belonging to the family Pantolestidae. Their diet consisted of other semi-aquatic life forms.

Theriiformes

Theriiformes is a subclass of mammals. The term was coined in 1997 by McKenna & Bell in their classification of mammals. In the strict sense, it is defined as all mammals more closely related to therians than to monotremes.

Tribosphenida

Tribosphenida is a group (infralegion) of mammals that includes the ancestor of Hypomylos, Aegialodontia and Theria (the last common ancestor of marsupials and placentals plus all of its descendants). Its current definition is more or less synonymous with Boreosphenida.

Zalambdalestidae

Zalambdalestidae is a clade of Asian eutherians occurring during the Late Cretaceous. Once classified as Glires, features like epipubic bones and various cranial elements have identified these animals as outside of Placentalia, representing thus a specialised clade of non-placental eutherians without any living descendants, and potentially rather different from modern placentals in at least reproductive anatomy.

Zatheria

Zatheria is a group (sublegion) of mammals that includes the common ancestor of Arguimuridae, Vincelestidae, Peramuridae and Tribosphenida (living therians plus all of its ancestors).

Extant mammal orders
Yinotheria
Theria

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