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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 ...
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.
The female lays a single soft-shelled, leathery egg 22 days after mating, and deposits it directly into her pouch. An egg weighs 1.5 to 2 grams (0.05 to 0.07 oz) [21] and is about 1.4 centimetres (0.55 in) long. While hatching, the baby echidna opens the leather shell with a reptile-like egg tooth. [22]
Australia is home to two of the five extant species of monotremes and the majority of the world's marsupials (the remainder are from Papua New Guinea, eastern Indonesia and the Americas). The taxonomy is somewhat fluid; this list generally follows Menkhorst and Knight [ 1 ] and Van Dyck and Strahan, [ 2 ] with some input from the global list ...
They hold the eggs internally for several weeks, providing nutrients, and then lay them and cover them like birds. Like marsupial "joeys", monotreme "puggles" are larval and fetus-like, [9] as like them they cannot expand their torso due to the presence of epipubic bones, forcing them to produce undeveloped young.
Such choices were inspired by media underuse, as well as to exploit the animal's striking appearance; [140] additionally, show creator Dan Povenmire, who also wrote the character's theme song, said that its opening lyrics are based on the introductory sentence of the Platypus article on Wikipedia, copying the "semiaquatic egg-laying mammal ...
Reptile eggs, bird eggs, and monotreme eggs are laid out of water and are surrounded by a protective shell, either flexible or inflexible. Eggs laid on land or in nests are usually kept within a warm and favorable temperature range while the embryo grows. When the embryo is adequately developed it hatches, i.e., breaks out of the egg's shell.