Reptiles are cold-blooded vertebrates that diverged from ancestral amphibians about 340 million years ago during the Carboniferous Period. Early reptiles included organisms such as Hylonomus, Petrolacosaurus, Archaeothyris and Paleothyris. The oldest evidence of reptiles is a set of footprints found in Nova Scotia. Two characteristics distinguish early reptiles from amphibians: scales and the ability to lay hard-shelled amniotic eggs.
Reptiles include turtles, squamates, crocodiles and tuataras. There are about 8,000 species of reptiles alive today. Of the four reptile groups, the squamates (amphisbaenians, lizards and snakes) are the most diverse with nearly 7,600 species.
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