World Library  
Flag as Inappropriate
Email this Article

Eutheria

Article Id: WHEBN0000216676
Reproduction Date:

Title: Eutheria  
Author: World Heritage Encyclopedia
Language: English
Subject: Evolution of mammals, Afrosoricida, Lagomorpha, Soricomorpha, Xenarthra
Collection: Late Jurassic First Appearances, Mammal Taxonomy
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Eutheria

Eutherians
Temporal range: Late JurassicHolocene, 160–0 Ma
Є
O
S
D
C
P
T
J
K
Pg
N
Juramaia
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Sublegion: Zatheria
Infralegion: Tribosphenida
Subclass: Theria
Clade: Eutheria
Gill, 1872 Huxley, 1880
Subgroups

Eutheria (; from Greek εὐ-, eu- "true/good" 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 Virginia opossum, from North America, which is a metatherian, all 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 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]

Characteristics

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

The Virginia opossum is the only non-Eutherian mammal to be found outside Australasia or South America

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 fossil eutherian species believed to be the oldest known is Juramaia sinensis, which lived about .[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

Mammaliformes

Other mammaliformes



Hadrocodium

Mammals
Australosphenids

Other
Australosphenids


Monotremes




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: 1–17.  
  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.  
  3. ^ a b Luo, Z.; C. Yuan; Q. Meng; Q. Ji (2011). "A Jurassic eutherian mammal and divergence of marsupials and placentals".  
  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. and Georgi, J.A. (April 2002). "The earliest known eutherian mammal". Nature 416 (6883): 816–822.  
  6. ^ Rose, Kenneth D. (2006). The beginning of the age of mammals. Baltimore: Johns Hopkins University Press.  
  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.  
  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". Bulletin of the American Museum of Natural History 327: 1–123.  
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 



Copyright © World Library Foundation. All rights reserved. eBooks from World eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.