|Placental mammals / Eutheria|
Fossil range: Early Cretaceous - Recent
House Mouse, Mus musculus
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.)
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.
Compare and contrast
Notes and references
bg:Плацентни ca:Euteri cs:Placentálové de:Höhere Säugetiere eo:Placentuloj hr:Viši sisavci hu:Méhlepényesek id:Eutheria it:Eutheria ko:진수하강 lb:Héijer Mamendéieren lij:Placentalia nl:Placentadieren no:Placentale pattedyr oc:Eutheria sl:Višji sesalci sv:Högre däggdjur th:ยูเธอเรีย zh-yue:真獸亞綱