Labyrinthodonts also lived during the Coal Age. Some had body structures like those of reptiles. Many labyrinthodonts were as large as alligators, while some were as small as salamanders. Reptiles represented the next step in animal development. On the evolutionary scale, they stand between the amphibians and the birds and mammals.
Reptiles are vertebrates that breathe air and are covered with scales rather than hair or feathers.
Cotylosaurs, extinct today, were probably the first reptiles, dating perhaps from about 300 million years ago. Reptiles made the final break with life in the water. They lived entirely on land and thus could move to areas that lay far from seas and rivers. Reptiles also developed hard-shelled eggs that they could lay almost anywhere on the ground. The earliest insects crawled but did not fly.