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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 ...
Monotremes (/ ˈ m ɒ n ə t r iː m z /) are mammals of the order Monotremata. They are the only group of living mammals that lay eggs, rather than bearing live young. The extant monotreme species are the platypus and the four species of echidnas. Monotremes are typified by structural differences in their brains, jaws, digestive tract ...
Ornithorhynchoidea is a superfamily of mammals containing the only living monotremes, the platypus and the echidnas, as well as their closest fossil relatives, to the exclusion of more primitive fossil monotremes of uncertain affinity.
However, the five species of monotreme, the platypuses and the echidnas, lay eggs. The monotremes have a sex determination system different from that of most other mammals. [ 2 ] In particular, the sex chromosomes of a platypus are more like those of a chicken than those of a therian mammal.
This category contains articles about all taxa below the subclass/order Monotremata - the platypus, the echidnas, and extinct species which are only known via fossil evidence. Subcategories This category has the following 5 subcategories, out of 5 total.
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Steropodon is a genus of prehistoric platypus-like monotreme, or egg-laying mammal. It contains a single species, Steropodon galmani, that lived about 100.2–96.6 million years ago during the Cretaceous period, from early to middle Cenomanian. [1] It is one of the oldest monotremes discovered, and is one of the oldest Australian mammal
Monotremes were historically classified within the clade Prototheria, alongside morganucodontids, docodonts, triconodonts and multituberculates, however it is now widely recognised that this grouping is a paraphyletic grade and that these groups do not share a close relationship. In 2001, Luo et al proposed the clade Australosphenida to include ...