|Lycopsis longirostris, an extinct Sparassodont, relatives of the marsupials|
|Orders and infraclasses|
The group was first proposed by Thomas Henry Huxley in 1880. It is nearly synonymous with the earlier taxon Marsupialia, but it also contains the nearest fossil relatives of marsupial mammals.
The closest relatives of the metatheres are the Eutheria (also erected by Huxley in 1880). Both are together united as infraclasses in the subclass Theria. The Theria contains all living mammals except monotremes.
During development, metatherians produce a yolk sac placenta and give birth to 'larval-like' offspring.
These offspring have underdeveloped rear limbs, and after birth they migrate to the marsupium where they attach to a nipple. The mouth of newly born metatherians forms an "O" shape into which the mother's nipple fits. Then the nipple swells to secure the offspring in place.
Evolutionary history[change | change source]
Metatherians first appeared in the Cretaceous period. Some stem group metatherians persisted well into the Neogene period before becoming extinct. Crown group marsupials, the one branch of Metatheria that survives today, diversified close to the time of extinction at the end of the Cretaceous.
References[change | change source]
- Szalay, Frederick S. (2006). Evolutionary history of the marsupials and an analysis of osteological ... ISBN 9780521025928.
- Clemens W.A. 1968. Origin and early evolution of marsupials. Evolution 22 1, 1-18.
- Luo, Zhe-Xi; et al. (2003). "An early Cretaceous tribosphenic mammal and metatherian evolution". Science. 302 (5652): 1934–1940. Bibcode:2003Sci...302.1934L. doi:10.1126/science.1090718. PMID 14671295. S2CID 18032860. Retrieved 2010-12-27.
- O'Leary, Maureen A. et al 2013. The placental mammal ancestor and the post–K-Pg radiation of placentals. Science 339 (6120): 662–667. 
- Horovitz, Inés; et al. (2009). "Cranial anatomy of the earliest marsupials and the origin of opossums". PLOS ONE. 4 (12): e8278. Bibcode:2009PLoSO...4.8278H. doi:10.1371/journal.pone.0008278. PMC 2789412. PMID 20016823.