This subject category encompasses all books on reptiles and amphibians, which includes frogs, toads, salamanders, newts, and caecilians, as well as snakes, lizards, turtles, and crocodiles. They are combined here because, historically, the zoological discipline of herpetology studied both these orders.
What these two groups share is that both are cold-blooded (ectothermic), four-limbed (tetrapod) vertrebrates (or in the case of snakes, have descended from four-limbed ancestors). They differ, however, in amphibians being dependent on water bodies for their larvae (bar a few exceptions), as their eggs have no shell. One of the key innovations in reptile evolution has been that of the egg shell, allowing them to live in drier climates, such as deserts.
