Echidnas, sometimes known as spiny anteaters, are quill-covered monotremes (egg-laying mammals) belonging to the family Tachyglossidae. 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. The diet of some species consists of ants and termites, but they are not closely related to the true anteaters of the Americas, which (along with sloths and armadillos) are xenarthrans. Echidnas live in Australia and New Guinea.
Echidnas evolved between 20 and 50 million years ago, descending from a platypus-like monotreme. This ancestor was aquatic, but echidnas adapted to life on land.
Echidnas do not tolerate extreme temperatures; they use caves and rock crevices to shelter from harsh weather conditions. Echidnas are found in forests and woodlands, hiding under vegetation, roots or piles of debris. They sometimes use the burrows of animals such as rabbits and wombats. Individual echidnas have large, mutually overlapping territories.