The Full Wiki

Eutheria: Wikis

Advertisements
  
  

Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! This article doesn't yet, but we're working on it! See more info or our list of citable articles.

Encyclopedia

From Wikipedia, the free encyclopedia

Eutheria
Fossil range: 125–0 Ma
Early Cretaceous – Recent
Fossil of Eomaia, the oldest known eutherian
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Subclass: Theria
Infraclass: Eutheria
Thomas Henry Huxley, 1880
Orders[1]

Eutheria (Greek: "true beasts") are a group of mammals consisting of placental mammals plus all extinct mammals that are more closely related to living placentals (such as humans) than to living marsupials (such as kangaroos). They are distinguished from non-eutherians by various features of the feet, ankles, jaws and teeth. One of the major differences between placental and non-placental eutherians is that placentals lack epipubic bones, which are present in all other fossil and living mammals.

The earliest known fossil eutherian, Eomaia was found in Asia and is dated to the Early Cretaceous period, about 125 million years ago.

Contents

Definition

Eutherians are a group of mammals consisting of placental mammals plus all extinct mammals that are more closely related to living placentals (such as humans) than to living marsupials (such as kangaroos).[2]

There are no living non-placental eutherians, and so knowledge of their synapomorphies ("defining features") is entirely based on a few fossils – which means the reproductive features that distinguish modern placentals from other mammals cannot be used in defining the eutheria. The features of eutheria that distinguish them from metatherians, a group that includes modern marsupials, are:

  • an enlarged malleolus ("little hammer") at the bottom of the tibia, the larger of the two shin bones.[2]
  • the joint between the first metatarsal bone and the entocuneiform bone in the foot is offset further back than the joint between the second metatarsal and mesocuneiform bones – in metatherians these joints are level with each other.[2]
  • various features of jaws and teeth.[2]

Reproductive features are also of no use in identifying fossil placental mammals, which are distinguished from other eutherians by:

  • the presence of a malleolus at the bottom of the fibula, the smaller of the two shin bones.[2]
  • a complete mortise and tenon upper ankle joint, where the rearmost bones of the foot fit into a socket formed by the ends of the tibia and fibula.[2]
  • a wide opening at the bottom of the pelvis, which allows the birth of large, well-developed offspring. Marsupials have and non-placental eutherians had a narrower opening that allows only small, immature offspring to pass through.[3]
  • the absence of epipubic bones extending forwards from the pelvis, which are not found in any placental, but are found in all other mammals – non-placental eutherians, marsupials, monotremes and mammaliformes – and even in the cynodont therapsids that are closest to mammals. Their function is to stiffen the body during locomotion.[4] This stiffening would be harmful in pregnant placentals, whose abdomens need to expand.[5]

Subgroups

Eutheria


Euarchontoglires



Laurasiatheria





Xenarthra



Afrotheria




A likely phylogeny (Atlantogenata and Boreoeutheria).[6][7][8] Alternative
hypotheses place either Xenarthra (and Epitheria)
or Afrotheria (and Exafroplacentalia (Notolegia)) at the base of the tree.
Eutheria  

Afrotheria


  Exafroplacentalia  

Xenarthra



Boreoeutheria  




[9]

These are the subgroups of extant members of Eutheria:

These groups together make up the crown group Placentalia (placental mammals). Eutheria also includes now extinct lineages that lie outside of Placentalia (see below).[10]

Evolutionary history

The earliest known eutherian species is the extinct non-placental Eomaia scansoria from the Lower Cretaceous of China, dated to about 125 million years ago. Some of its fossils show thick fur. Montanalestes was found in North America, while all other non-placental eutherian fossils have been found in Asia. The earliest known placental fossils have also been found in Asia.[2]
Millions of years ago
= Placentals      = Other eutheria
Origin
of
eutheria
    = Asian fossils         = N American fossils
    = Period when placental classes diverged according to molecular phylogenetics estimates
Murtoilestes
Prokennalestes
Montanalestes
Ukhaatherium
Asioryctes
Daulestes
Aspanestes
Eoungulatum
Gypsonictops
Fossil record of Cretaceous eutheria[2]
Simplified, non-systematic, outline of evolution of eutheria from cynodont therapsids.[2]
† = extinct

Notes and references

  1. ^ "Eutheria phylogeny". Mikko's Phylogeny Archive. http://www.helsinki.fi/~mhaaramo/metazoa/deuterostoma/chordata/synapsida/eutheria/eutheria_index.html. Retrieved 2008-07-24. 
  2. ^ a b c d e f g h i Ji, Q., Luo, Z-X., Yuan, C-X.,Wible, J.R., Zhang, J-P.,and Georgi, J.A. (April 2002). "The earliest known eutherian mammal". Nature 416: 816–822. doi:10.1038/416816a. http://www.nature.com/nature/journal/v416/n6883/full/416816a.html. Retrieved 2008-09-24. 
  3. ^ Weil, A. (April 2002). "Mammalian evolution: Upwards and onwards". Nature 416: 798–799. doi:10.1038/416798a. http://www.nature.com/nature/journal/v416/n6883/full/416798a.html. Retrieved 2008-09-24. 
  4. ^ Reilly, S.M., and White, T.D. (January 2003). "Hypaxial Motor Patterns and the Function of Epipubic Bones in Primitive Mammals". Science 299 (5605): 400–402. doi:10.1126/science.1074905. http://www.sciencemag.org/cgi/content/full/299/5605/400. Retrieved 2008-09-24. 
  5. ^ Novacek, M.J., Rougier, G.W, Wible, J.R., McKenna, M.C, Dashzeveg, D.,and Horovitz, I. (October 1997). "Epipubic bones in eutherian mammals from the Late Cretaceous of Mongolia". Nature 389: 483–486. doi:10.1038/39020. http://www.nature.com/nature/journal/v389/n6650/full/389483a0.html. Retrieved 2008-09-24. 
  6. ^ Wildman DE, Uddin M, Opazo JC, et al (2007). "Genomics, biogeography, and the diversification of placental mammals". Proc. Natl. Acad. Sci. U.S.A. 104 (36): 14395–400. doi:10.1073/pnas.0704342104. PMID 17728403. http://www.pnas.org/content/104/36/14395.full. 
  7. ^ Murphy WJ, Pringle TH, Crider TA, Springer MS, Miller W (2007). "Using genomic data to unravel the root of the placental mammal phylogeny". Genome Res. 17 (4): 413–21. doi:10.1101/gr.5918807. PMID 17322288. http://genome.cshlp.org/content/17/4/413.long. 
  8. ^ Schneider A, Cannarozzi GM (2009). "Support Patterns from Different Outgroups Provide a Strong Phylogenetic Signal". Mol. Biol. Evol.. doi:10.1093/molbev/msp034. PMID 19240194. 
  9. ^ Churakov G, Kriegs JO, Baertsch R, Zemann A, Brosius J, Schmitz J (2009). "Mosaic Retroposon Insertion Patterns in Placental Mammals". Genome Res.. doi:10.1101/gr.090647.108. PMID 19261842. 
  10. ^ Archibald JD, Averianov AO, Ekdale EG (November 2001). "Late Cretaceous relatives of rabbits, rodents, and other extant eutherian mammals". Nature 414 (6859): 62–5. doi:10.1038/35102048. PMID 11689942. 

References

  • Goloboff, P.A.; Catalano, S.A.; Mirande, J.M.; Szumik, C.A.; Arias, J.S.; Källersjö, M & Farris, J.S. 2009. Phylogenetic analysis of 73 060 taxa corroborates major eukaryotic groups. Cladistics 25 (3): 211-230
Advertisements

Wiktionary

Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

Contents

Translingual

Etymology

From Ancient Greek εὖ (eu), good, true) + θηρίον (thērion), beast).

Proper noun

Wikipedia-logo.png
Wikipedia has an article on:

Wikipedia

Eutheria

  1. A taxonomic infraclass, within subclass Theria — the mammals that have placentas.
Wikispecies-logo.svg
Wikispecies has information on:

Wikispecies

See also


Wikispecies

Up to date as of January 23, 2010

From Wikispecies

Taxonavigation

Main Page
Cladus: Eukaryota
Supergroup: Unikonta
Cladus: Opisthokonta
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Cladus: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclassis: Tetrapoda
Classis: Mammalia
Subclassis: Theria
Infraclassis: Eutheria
Superordines: Xenarthra - Afrotheria - Euarchontoglires - Laurasiatheria

Name

Eutheria Gill 1872

Vernacular names

Català: Euteri
Česky: Živorodí
Deutsch: Höhere Säugetiere
English: Eutheria
Español: Eutérios
Français: Euthériens
한국어: 진수하강
Nederlands: Placentadieren
日本語: 真獣下綱
‪Norsk (bokmål)‬: Placentale pattedyr
Polski: Łożyskowce
Svenska: Placentadäggdjur
Українська: Плацентарні

References

Wikimedia Commons For more multimedia, look at Eutheria on Wikimedia Commons.

Simple English

Placental mammals/Eutheria
Fossil range: Middle Cretaceous - Recent
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Subclass: Theria
Infraclass: Eutheria
Orders[1]

Eutheria is the taxonomical name for a group of animals. This taxon contains the placental mammals, such as humans. The name Eutheria comes from the Greek words eu- "well-developed" and ther "beast". Eutheria was introduced by Thomas Henry Huxley in 1880. Members of Eutheria are found on all continents and in all oceans.

All living Eutherians are placental mammals. This means that a Eutherian fetus is fed during gestation by a placenta. The offspring of Eutherians are carried in the mother's uterus until fully developed.

Eutherians are different from other mammal groups such as monotremes and marsupials which are not placental. Monotremes, for example, lay eggs which protect the young until they are fully developed. Marsupials give birth to young who are not completely developed. Their young then move to a special pouch in the mother's body to continue their development.

The earliest known eutherian species is the extinct Eomaia scansoria from the Lower Cretaceous in China.

Other pages

Notes and references

  1. "Eutheria phylogeny". Mikko's Phylogeny Archive. http://www.fmnh.helsinki.fi/users/haaramo/Metazoa/Deuterostoma/Chordata/Synapsida/Eutheria/Eutheria_1.htm#Edentata. Retrieved 2006-03-08. 
Look up Eutheria in Wikispecies, a directory of species


Advertisements






Got something to say? Make a comment.
Your name
Your email address
Message