Tetrapods (“four feet”) is a term used to describe the four-legged creatures that left the water to live on land. The first tetrapods were the amphibians; dinosaurs were also tetrapods. In fact, all modern amphibians, reptiles, birds, and mammals are tetrapods. (Interestingly, some scientists say humans can be considered tetrapods, as they are descendants of the original tetrapods; we have four limbs, though we use two of them as arms instead of for walking.)