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Brief Summary

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Eutherians make up the largest of the three mammal lineages.This lineage is composed of all extant placental mammals (Placentalia) and all extinct nonplacental animals that are more closely related to the Placentalia than they are to other two mammal lineages.Metatheria (the marsupials) and Monotremata (the egg-laying mammals).

Of the approximately 5400 species of extant mammals, eutherians (placentals) make up 90%.All mammals endemic to the old world (Europe, Africa, Asia) and all but one species (the Virginia opossum, Didelphis virginiana) endemic to North America north of Mexico are placental mammals.Australia houses approximately the same number of placental mammals and marsupials.Most Australian placentals are species from the two most speciose placental orders: bats (Chiroptera) and rodents (Rodentia), which together make up almost half of all modern mammal species.Australia is unique in that all monotremes live only on this continent.The mammal fauna of Central and South America is dominated by placental species, but also includes the approximate 100 species of placentals outside of Australia (Archibald 2005).23 species of mammal are currently native to Antartica, all are marine.These include seals, whales and dolphins.However, fossil eutherians discovered from Antarctica reveal that its historic climate supported a diversity of terrestrial mammals (Gelfo et al. 2015).

Several features distinguish eutherians from noneutherian mammals, including numbers of teeth (adult eutherians have three molars and five premolars whereas metatherians have four molars and three premolars; adult monotremes do not have teeth) and various features of their feet, ankles, and jaws (Archibald 2005; Wikipedia 2014).

The oldest known eutherian species is the 160 million year old Juramaia sinensis, an extinct non-placental insectivore known from an almost complete fossil discovered in 2011 from the Jurassic terrestrial shale Tiaojishan Formation of Liaoning province, China (Luo et al. 2011).Before Juramaia was discovered the earliest known eutherian fossil was Eomaia, which dated the Eutherian origin to the considerably more recent (125 million year old) cretaceous.Genetic studies support the date of the eutherian-metatherian split at about 160 million years ago, and predicted the existence of a eutherian ancestor from this period even before the fossil was found; so the finding closes a significant evolutionary gap, gives new insight into the evolution of early mammals, and helps calibrate the mammalian molecular clock (Luo et al 2011; Wikipedia 2014).

Reference

Gelfo, J.N., Moers, T., Lorente, M., Lopez, G.M. and Reguero, M., 2015. The oldest mammals from Antarctica, early Eocene of the La Meseta Formation, Seymour Island. Palaeontology, 58(1), pp.101-110.

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ADW: Eutheria: CLASSIFICATION

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This is a link to the classification of Eutherians.

Eutheria

provided by wikipedia EN

Eutheria (/jˈθɪəriə/; from Greek εὐ-, eú- 'good, right' and θηρίον, thēríon 'beast'; lit.'true beasts') is the clade consisting of all therian mammals that are more closely related to placentals than to marsupials.

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 early Late Jurassic (Oxfordian) of 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]

Characteristics

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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 innermost 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.
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Eutheria: Brief Summary

provided by wikipedia EN

Eutheria (/juːˈθɪəriə/; from Greek εὐ-, eú- 'good, right' and θηρίον, thēríon 'beast'; lit. 'true beasts') is the clade consisting of all therian mammals that are more closely related to placentals than to marsupials.

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.

The oldest-known eutherian species is Juramaia sinensis, dated at 161 million years ago from the early Late Jurassic (Oxfordian) of China.

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

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Wikipedia authors and editors
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