Monotreme

A monotreme is an egg-laying mammal in the order Monotremata. Living monotremes are platypuses and echidnas, which nurse their young with milk but lack nipples.

Mammal: A vertebrate that has hair and produces milk to nourish its young. Monotremes are mammals despite laying eggs rather than giving birth to live young.
Platypus: A semiaquatic Australian monotreme with a broad bill, webbed feet, and venomous ankle spurs in males. Its aquatic feeding and electroreception show one specialized monotreme lifestyle.
Mammal evolution: The evolutionary history of mammals from their synapsid ancestors to living groups. Monotreme origins belong to the early diversification of mammals.
Short-beaked echidna: An echidna species widespread across Australia and parts of New Guinea. It is the most widely distributed living monotreme.
Platypus genome: The complete genetic sequence of the platypus, published in 2008. Its mix of mammalian and reptile-like genetic features offers evidence about monotreme ancestry.
Monotremata: The order of mammals comprising platypuses, echidnas, and their extinct relatives. This taxonomic order contains every living monotreme.
Echidna: A spiny, ant-eating monotreme native to Australia and New Guinea. Echidnas show how monotremes adapted egg-laying mammalian biology to life on land.
Molecular clock: A method that estimates evolutionary divergence times from genetic differences and mutation rates. Genetic comparisons help estimate when monotremes diverged from other mammalian lineages.
Long-beaked echidna: A group of three echidna species native to New Guinea, classified in the genus Zaglossus. These species extend monotreme diversity beyond Australia.
Mammalian reproduction: The reproductive processes by which mammals produce and nurture offspring. Monotremes broaden the picture of mammalian reproduction with egg-laying and milk-feeding.

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