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What are Monotremes?

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What are Monotremes?

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• Monotremes are mammals that lay eggs instead of giving birth to live young. The only extant monotremes are the platypus and two species of anteater that live in Australia and New Guinea.

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Monotremes are egg-laying mammals that maintain a relatively low body temperature and share some skeletal features with early mammals. These traits suggest that monotremes have been evolving on their own, apart from placentals and marsupials, for some time. There are only three living species, which are found only in New Guinea and Australia: the platypus and two species of echidna, the spiny anteater. There have been very few fossils of monotremes discovered to date, but the oldest fossils, some jaw fragments, have been found in Early Cretaceous rocks.First known fossil occurrence: Cretaceous.Last known fossil occurrence: Quaternary. This group has living relatives.

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Monotremes (“one hole,” referring to their genitals) are members of Order Monotremata, the smallest of three groups of mammals (the others being marsupials and placentals), and the most distantly related to other living mammals. Monotremes split off from other mammals about 150 million years ago. By contrast, marsupials and placental mammals split from each other about 90 million years ago. Although monotremes were once a larger group, today they only consist of just five species: the platypus, short-beaked echidna, Western long-beaked echidna, Sir David’s long-beaked echidna, and the Eastern long-beaked echidna. All of them are only found in Australia and New Guinea, but there is evidence that at one point, monotremes were probably global in extent. Some taxonomists propose putting platypi and echnidnas into two separate orders. Monotremes share many features of earlier amniotes, such as the ancestors of mammals: they have a single hole for doing all their business, a low metabolic ra

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