The platypus is an egg-laying mammal of the family Platypidae. The mouth is flat and protruding, shaped like a duckbill, covered with animal hair, hence the name. There are webbed feet on five toes Like a bird, it lays eggs and feeds its young like a mammal, but its mother has no nipple and only a small hole that secretes mammary glands. The cubs licked the milk from the wet hair on their mother's abdomen. Platypus can snorkel, usually nesting on the banks of swamps or rivers, and the caves are open underwater. When feeding, dive into the water and explore shellfish, worms and crustaceans in the mud with your mouth. Found in southern Australia and Tasmania, it lives in a semi-water and semi-land environment. Because Australia was separated from other continents about 200 million years ago, isolated in the ocean of the southern hemisphere, with simple natural conditions and slow animal evolution, platypus is an animal with ancient and low-level characteristics and has become a rare animal unique to Australia. This is of great significance to the study of animal evolution and geographical distribution. The platypus is an ancient living mammal. Although it is not the ancestor of mammals, it occupies an important position in the evolutionary history of animals. The platypus has hair on its body surface and feeds its offspring with milk, which has the characteristics of mammals; Platypus reproduce by laying eggs, just like reptiles. Therefore, it can be regarded as one of the evidences that mammals evolved from reptiles, and it is called the living fossil of the animal kingdom.