monotremes, the only mammals that lay eggs instead of giving birth to live young. All are long-lived, with low rates of reproduction and relatively prolonged parental care of infants.
Like other mammals, monotremes are warm-blooded, but lay eggs. However, the egg is retained for some time within the mother, who actively provides the egg with nutrients. Monotremes also lactate, but have no defined nipples, excreting the milk from their mammary glands via openings in their skin.
The venomous, duck-billed, egg-laying, beaver-tailed, otter-footed platypus is the only living representative of its family (Ornithorhynchidae) and genus (Ornithorhynchus).
Scientists believe all mammals evolved from reptiles, and the animals that became platypuses and those that became humans shared an evolutionary path until about 165 million years ago when the platypus branched off. Unlike other evolving mammals, the platypus retained characteristics of snakes and lizards, including the pain-causing poison that males can use to ward off mating rivals.
Recent research took a closer look at the platypus genome to try and unravel DNA that seems to mix different classifications of animals. Then by comparing platypus genes to those of humans and other mammals, scientists hope to fill in gaps in knowledge about mammals' evolution and better identify certain species' specific traits.