AskDefine | Define eutherian

Dictionary Definition

eutherian adj : of or relating to or belonging to the subclass Eutheria; "eutherian mammals" n : mammals having a placenta; all mammals except monotremes and marsupials [syn: placental, placental mammal, eutherian mammal]

User Contributed Dictionary

English

Adjective

  1. belonging or pertaining to the group Eutheria, comprising the placental mammals.

Noun

  1. a eutherian animal.

Extensive Definition

Eutheria is a taxon containing the placental mammals, such as humans. The sister group of Eutheria is Metatheria, which includes marsupials and their extinct relatives.

Origin of the word

The name Eutheria comes from the Greek words eu- "well[-developed]" and ther "beast". When Eutheria was introduced by Thomas Henry Huxley in 1880, he meant it to be broader in definition than its precursor Placentalia. Some use Eutheria as a total group which includes the crown group Placentalia and extinct mammals which are closer to Placentalia than to Marsupialia.

Characteristics of eutherians

Nevertheless, all living eutherians are placental mammals. This means that a eutherian fetus is nourished during gestation by a placenta. Eutherians are also viviparous, meaning that the offspring are carried in the mother's uterus until fully developed.

Differences from other mammals

Because of this, eutherians are different from other mammal groups such as monotremes and marsupials which are not placental. Monotremes, for instance, lay eggs which protect developing young until they are fully developed. Marsupials give birth to partially-developed young who then migrate to a special pouch in the mother's body in which the young continue their development. (Some exceptions do exist. Bandicoots for instance, which are marsupials, develop small placenta-like structures during gestation.)

Earliest example

The earliest known eutherian species is the extinct Eomaia scansoria from the Lower Cretaceous of China. It is a member of Eutheria, but the hips of the animal were too narrowly built to have allowed the birth of well-developed young. Thus it is unlikely that a placenta greatly contributed to the development of E. scansoria's young before they were born.
Members of Eutheria are found on all continents and in all oceans.

See also

Compare and contrast

Notes and references

Detailed cladogram of Eutheria from Proceedings of the National Academy of Sciences, February 4, 2003, vol. 100, no. 3, pp. 1056-1061.
eutherian in Bulgarian: Плацентни
eutherian in Catalan: Euteri
eutherian in Czech: Placentálové
eutherian in German: Höhere Säugetiere
eutherian in Esperanto: Placentuloj
eutherian in Spanish: Placentalia
eutherian in French: Placentalia
eutherian in Croatian: Viši sisavci
eutherian in Hungarian: Méhlepényesek
eutherian in Indonesian: Eutheria
eutherian in Italian: Eutheria
eutherian in Japanese: 真獣下綱
eutherian in Korean: 진수하강
eutherian in Luxembourgish: Héijer Mamendéieren
eutherian in Ligurian: Placentalia
eutherian in Dutch: Placentadieren
eutherian in Norwegian: Placentale pattedyr
eutherian in Occitan (post 1500): Eutheria
eutherian in Polish: Łożyskowce
eutherian in Portuguese: Placentários
eutherian in Romanian: Eutheria
eutherian in Russian: Плацентарные
eutherian in Slovenian: Višji sesalci
eutherian in Swedish: Högre däggdjur
eutherian in Thai: ยูเธอเรีย
eutherian in Chinese: 真獸下綱
eutherian in Contenese: 真獸亞綱
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