Monotremes have highly modified snouts or beaks, and modern adult monotremes have no teeth. Like other mammals, however, monotremes have a single bone in their lower jaw, three middle ear bones, high metabolic rates, and hair, and they produce milk to nourish the young.
The echidna (see diagram) lays a tiny egg (1) that is soft-shelled and resembles a reptile's egg. Once the egg is laid, the echidna uses its hind limbs to roll it to a special incubation groove (2). The minute hatchling is about 1.25 cm (0.5 in.) long.
Related category• ZOOLOGY
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