Yes, reptiles were the first group of vertebrates to become true land animals. They had several adaptations: Legs were arranged to support the body’s weight more effectively than in amphibians, allowing reptile bodies to be larger and to be able to run. Reptilian lungs were more developed, with a greatly increased surface area for gas exchange than the saclike lungs of amphibians. The three-chambered heart of reptiles was more efficient than the amphibian heart. In addition, the skin was covered with hard, dry scales to minimize water loss. However, the most important evolutionary adaptation was the amniotic egg, in which an embryo could survive and develop on land. The eggs were surrounded by a protective shell that prevented the developing embryo from drying out.