Reptiles originated about 320-310 million years ago in the steaming swamps of the Carboniferous period. They evolved from a group of amphibians known as the Labyrinthodonts (because of the maze-like structure of their teeth). These amphibians became increasingly adapted to dry land, and spent less time in the water. Their skin developed dry scales and they also began to lay dry, hard-shelled eggs on land rather than in water. Their offspring hatched as well-developed "mini adults" without having to go through a tadpole stage. As the Earth began to experience a drying trend at the end of the Carboniferous, early reptiles fared better than their amphibian counterparts. Reptiles would become the dominant land animals into the Permian period and throughout the Mesozoic Era in the form of dinosaurs.