A tetrapod is a four-legged animal, such as a mammal, reptile, or amphibian. The term “tetrapod” comes from the Greek words for “four” and “foot.” Most land animals are tetrapods, including humans.
Tetrapods evolved from fish during the Devonian period, about 375 million years ago. The first tetrapods were aquatic and had tails. They gradually adapted to life on land, losing their tails and developing legs with toes.
Today, there are about 12,000 species of tetrapods, including mammals (such as humans, elephants, and bats), reptiles (such as snakes and crocodiles), birds (such as chickens and ducks), and amphibians (such as frogs and salamanders).
Tetrapods are characterized by several features that distinguish them from fish. Tetrapods have lungs for breathing air; they have a backbone made of bones; their limbs are supported by muscles; they have skin covered in scales or feathers; and they lay eggs on land.