The Order Monotremata comprises the most primitive group of living mammals, including the platypus and echidnas. Unlike most mammals, monotremes lay eggs instead of giving birth to live young, yet they still produce milk to nourish their offspring. They possess a mix of reptilian and mammalian traits, such as a cloaca (single opening for excretion and reproduction) and a leathery or spiny body covering in echidnas. Monotremes are found only in Australia and New Guinea, are generally insectivorous or aquatic feeders, and provide important insights into early mammalian evolution.