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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 ...
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 ...
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.
Together with the four species of echidna, it is one of the five extant species of monotremes, mammals that lay eggs instead of giving birth to live young. [6] Like other monotremes, the platypus has a sense of electrolocation, which it uses to detect prey in cloudy water. [7]
The eastern long-beaked echidna is a member of the order Monotremata. Although monotremes have some of the same mammal features such as hair and mammary glands, they do not give birth to live young, they lay eggs. Like birds and reptiles, monotremes have a single opening, the cloaca. The cloaca allows for the passage of urine and feces, the ...
The four extant species of echidnas and the platypus are the only living mammals that lay eggs and the only surviving members of the order Monotremata. [3] The diet of some species consists of ants and termites, but they are not closely related to the American true anteaters or to hedgehogs. Their young are called puggles.
Among mammals, monotremes (four species of echidna, and the platypus) are uniquely oviparous. In all but special cases of both ovuliparity and oviparity, the overwhelming source of nourishment for the embryo is the nutrients stored in the yolk, pre-deposited in the egg by the reproductive system of the mother (the vitellogenesis).
The mammals included are only viviparous (marsupials and placentals) as some mammals, which are monotremes (including platypuses and echidnas) lay their eggs. A marsupial has a short gestation period, typically shorter than placental. For more information on how these estimates were ascertained, see Wikipedia's articles on gestational age.