Platypus, a mammal. It is about 0.5 meters long and has soft brown dense hair outside. The snout is flat, shaped like a duckbill, with wide horny gums in the mouth, but no teeth. Each limb has five toes, and there are membranous webs between the toes. The tail is large and flat, accounting for 1/4 of the body length, and plays the role of rudder when swimming in the water. The platypus is a very strange small mammal. Although mothers also secrete milk to feed their young, they are not viviparous but oviparous. That is, the mother bird lays eggs and hatches by the temperature of the mother bird like a bird. The mother beast has no breasts and nipples, but secretes milk on both sides of the abdomen, and the cubs lie on the mother beast's abdomen and lick. Platypus can dive, usually nesting in swamps or rivers, and the nest holes are underwater. When feeding, dive into the water and explore shellfish, worms and crustaceans in the mud with your mouth. The platypus, which is distributed in southern Australia and Tasmania, is the most primitive mammal in existence, and it is an evolutionary link to form higher mammals, which has great scientific research value in animal evolution.