There are over 8000 reptile species in total, they belong to the class Reptilia, and are devided into four groups or orders.
Order Squamata 3 suborders
Suborder Sauria – over 4 700 species of lizards in about 20 families
Suborder Amphisbaenia – 168 species of amphisbaenians and worm lizards in 3-4 families
Suborder Serpentes – 2 900 species of snakes in 18 families
Order Testudians 238 species of turtles and tortoises in 12 families
Order Crocodylia 22 species of crocodiles and alligators in 1 family and 3 subfamilies
Order Rhynchocephalia 2 species of tuataras
Like mammals, birds, fish and amphibians, reptiles are vertebrates (animals with a backbone) They are ectotherms, meaning that they obtain their body heat from outside sources rather than producing it metabolically from their food. This ability separates them from mammals and birds, which are endothermic.
Reptiles are seperated from fish and amphibians in that they lay shelled eggs or produce live young, depending on species. This means that they are not bound to water, as are most amphibians and fish. Another major difference between the two are that reptiles are covered in dry, horny scales while amphibians have a wet porous skin that needs to be kept moist.