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The class Mammalia is divided into two subclasses based on reproductive techniques: egg-laying mammals (yinotherians or monotremes - see also Australosphenida), and mammals which give live birth . The latter subclass is divided into two infraclasses: pouched mammals ( metatherians or marsupials ), and placental mammals ( eutherians , for which ...
The traditional "Theria hypothesis" states that the divergence of the monotreme lineage from the Metatheria and Eutheria lineages happened prior to the divergence between marsupials and placentals, and this explains why monotremes retain a number of primitive traits presumed to have been present in the synapsid ancestors of later mammals, such ...
The class Mammalia is divided into two subclasses based on reproductive techniques: monotremes, which lay eggs, and therians, mammals which give live birth, which has two infraclasses: marsupials/metatherians and placentals/eutherians. See List of monotremes and marsupials, and for the clades and families, see Mammal classification ...
The study also indicated that some alleged Australosphenids were also "crown group" monotremes (e.g. Steropodon) and that other alleged Australosphenids (e.g. Ausktribosphenos, Bishops, Ambondro, Asfaltomylos) are more closely related to and possibly members of the Therian mammals (group that includes marsupials and placentals, see below). [55]
Placental mammals (infraclass ... like monotremes, marsupials and most other vertebrates, the urogenital ducts exit through the vulva or penis and the rectum opens as ...
Marsupials, along with monotremes (platypuses and echidnas), typically have lower body temperatures than similarly sized placentals , [12] with the averages being 35 °C (95 °F) for marsupials and 37 °C (99 °F) for placentals.
Eutheria (from Greek εὐ-, eú-'good, right' and θηρίον, thēríon 'beast'; lit. ' true beasts '), also called Pan-Placentalia, is the clade consisting of placentals and all therian mammals that are more closely related to placentals than to marsupials.
Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals.First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as well as many extinct non-marsupial relatives.