The British Triassic rocks are poor in fossils, as might be expected of salt lakes laid down in desert surroundings. However there are bones not only of fish but of a fair number of reptiles, and near the top of the system, of a little shrew-like beast classified as a mammal. The most important difference between amphibians and reptiles is that reptiles have eggs with tough shells which can be laid anywhere, while amphibians have shell-less eggs, which must be laid in water or very damp places. The Permian reptiles were fairly like modern ones, but some of them could stand up on their four legs so that their bellies did not touch the ground. This chapter discusses variety of reptiles, including the monstrous dinosaurs. This was the great age of reptiles. Dinosaurs up to 80 feet long lived on land, the largest probably living in swamps, but some walking on their hind legs like modern kangaroos.