What Are The Defining Features Of A Reptile?

Reptiles are a class of Vertebrates with over 6,600 species worldwide. The major groups are: Alligators and crocodiles, turtles, lizards and snakes.
Reptiles have unique traits that allow them to be easily distinguishable from other classes of animals.  They are separated from amphibians by the presence of an amniotic egg, from mammals by characteristics like the absence of milk and presence of scaly skin, and from birds by the absence of feathers.  Reptiles have scaly skin and most have complex, shelled, amniotic eggs that are internally fertilized.  All reptiles, with the exception of snakes, possess true claws.
All reptiles are ectotherms, meaning they maintain and alter their body temperature by acquiring heat from the environment.  As a result, reptiles do not need to rely on frequent eating to fulfill their basic bodily functions.  By contrast, mammals and birds are endotherms, meaning they use their food energy to maintain a constant body temperature, and therefore, must eat regularly.

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