 Unlike modern amphibians , many <unk> are covered in small , closely packed scales . The <unk> of most <unk> are covered in rows of large ventral plates . During early stages of development , they first have only small , rounded scales . <unk> show , as the animals grew , the scales on the <unk> of their bodies developed into large , wide ventral plates . The plates overlap each other in a way that allows a wide range of flexibility . Later <unk> <unk> , such as <unk> and <unk> , have no evidence of scales . They may have lost scales to make movement easier under water or to allow <unk> <unk> , the absorption of oxygen through the skin . 
