monotremeihin

Monotremes are an ancient and small lineage of egg-laying mammals, belonging to the order Monotremata. They are distinguished from other mammals by laying eggs, possessing a cloaca, and feeding their young with milk rather than nipples. Modern monotremes include two families: Ornithorhynchidae, which contains the platypus, and Tachyglossidae, which comprises echidnas. They generally have a relatively low metabolic rate and a body temperature lower than most placental mammals.

The two extant groups live in Australia and New Guinea. The platypus (Ornithorhynchus anatinus) inhabits rivers and lakes in eastern Australia and Tasmania and feeds on small aquatic animals. Echidnas (family Tachyglossidae) are mostly terrestrial, with the short-beaked echidna Tachyglossus aculeatus found across Australia, and the long-beaked echidnas (genus Zaglossus) occurring in New Guinea. Their habitats range from forest and scrub to desert regions.

Reproduction in monotremes is oviparous. The female lays eggs—one to several, depending on species—usually in a burrow or a temporary skin pouch, and the eggs hatch after about 10 days for platypus and a comparable period for echidnas. The young, called puggles, feed on milk produced by mammary glands, but monotremes lack nipples; the milk is secreted onto the skin or fur. Echidnas often have spines and a specialized snout, while the platypus has a duck-like bill and webbed feet.

Physiology and adaptations include the platypus’s electroreception in its bill and venomous spurs in males, alongside the echidnas’ specialized rostrum and dense coat. Monotremes are key to understanding early mammalian evolution, retaining several primitive features while remaining true mammals.

Evolution and conservation note that monotremes diverged early from other mammals. Fossil evidence includes early monotreme relatives such as Teinolophos and Steropodon. Today monotremes face habitat loss and climate pressures in parts of their range, with conservation status varying by species.