Vertebrates are divided into smaller groups that include fish, amphibians, reptiles, birds and mammals. A mammal is an animal that feeds its young milk produced in the mammary glands located on the mother. The development of mammary glands separates mammals from all other living things. Mammary glands are located on the belly, between the front or hind legs, of a female. Milk contains water, vitamins, fat, protein, and carbohydrates.
Hair is another feature separating mammals from other animals.
Hair comes in many forms, from the barbed quills of porcupines to the soft fur of a lemur. Birds All birds have feathers, making them different from all other animals. Birds have several types of feathers, from stiff contour feathers, which cover the wings and body, to fluffy down, which helps keep birds warm. Special contour feathers on the wings, called flight feathers, help to lift and maneuver birds in the air. All birds have wings - even ostriches and other flightless birds.