Monotremes

Monotremes

Monotremes (/mɒˈnɒtrɪmiːz/ from the Greek monos "single" + trema "hole", referring to the cloaca) are one of the three main groups of living mammals. They are typified by laying eggs rather than bearing live young, and include the platypus and four species of echidnas (or spiny anteaters).

Etymology

The term "monotreme" derives from the Greek words monos, meaning "single", and trema, meaning "hole". This refers to the single opening, or cloaca, that these animals have for the excretion of both wastes and the laying of eggs.

Characteristics

Monotremes are distinguished from other mammals in their methods of reproduction; they lay eggs instead of giving birth to live young. The eggs are leathery rather than hard, similar to those of reptiles. Other distinctive characteristics include a single bone in their lower jaw, and the fact that one of their ear bones, the stapes, is reptile-like, being derived from the jaw bones of their reptilian ancestors.

Species

There are only five extant species of monotremes: the platypus and four species of echidnas (or spiny anteaters). The platypus and the short-beaked echidna are found in Australia, while the three species of long-beaked echidnas are found in New Guinea.

Evolution

Monotremes are among the most primitive of mammals, with fossils dating back to the Cretaceous period. They are believed to have diverged from other mammals around 166 million years ago.

Conservation

While the platypus and short-beaked echidna are not considered threatened, the three species of long-beaked echidnas are listed as either vulnerable or critically endangered.

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