Monotremen

Monotremen, the German term for monotremes, denotes a small and primitive order of egg-laying mammals. Living monotremes include the platypus and echidnas, and they represent one of the earliest diverging mammalian lineages. They occur in Australia and New Guinea and retain several ancestral traits unusual among mammals.

The name monotreme derives from Greek monos "single" and trema "hole," referring to the single opening—the cloaca—sharing urinary, digestive, and reproductive tracts in these animals.

Taxonomy places living monotremes in two families: Ornithorhynchidae, containing the platypus (Ornithorhynchus anatinus), and Tachyglossidae, containing echidnas (Tachyglossus aculeatus and several Zaglossus species).

Monotremes are oviparous; females lay eggs and incubate them in burrows or nest chambers. They have a cloaca and mammary glands but no nipples; milk is secreted onto the skin or fur for the young to lap. The platypus possesses electroreceptors and, in males, a venomous spur.

Their distribution spans Australia and New Guinea; fossil relatives extend back to the Mesozoic. Monotremes are considered an early mammalian lineage, retaining primitive features such as a low metabolic rate and a tendency toward generalized dental patterns.

In ecology, platypuses are semi-aquatic and usually crepuscular, feeding on aquatic invertebrates; echidnas are mostly terrestrial, foraging on ants and termites. Some species face habitat pressures, and ongoing research tracks their status and evolutionary significance.