|The reptiles are a group of vertebrate animals. All reptiles
are tetrapods, they are all amniotes (animals whose embryos are surrounded
by an amniotic membrane). Today they are represented with four orders:
Reptiles are found on all continents except for Antarctica, although their main distribution comprises the tropics and subtropics. Reptiles don't have a constant body temperature. They are only able to a limited extent to actively regulate their body temperature, which is largely dependent on the environmental temperature. Most reptile species are carnivorous and oviparous (egg-laying). Some species are ovoviviparous, and a few species are truly viviparous.
However, note the below described taxonomy issues; mammals and birds are all descendants of reptiles.
Classification of reptiles
Reptiles classically included all the amniotes except birds and mammals. Thus reptiles were defined as the set of animals that includes crocodiles, alligators, tuataras, lizards, snakes, and turtles, grouped together as the class Reptilia. This is still the usual definition of the term.
However, in recent years many taxonomists have begun to insist that taxa should be monophyletic, that is, groups should include all descendants of a particular form. The reptiles as defined above would be paraphyletic, since they exclude both birds and mammals, although these also developed from the original reptile. Colin Tudge writes:
Some cladists thus redefine Reptilia as a monophyletic group, including both the classic reptiles as well as the birds and perhaps the mammals (depending on ideas about their relationships). Others abandon it as a formal taxon altogether, dividing it into several different classes. However, other biologists believe that the common characters of the standard four orders are more important than the exact relationships, or feel that redefining the Reptilia to include birds and mammals would be a confusing break with tradition. A number of biologists have adopted a compromise system, marking paraphyletic groups with an asterisk, e.g. class Reptilia*. Colin Tudge notes other uses of this compromise system: