Members of the class Reptilia (see reptile) that include turtles, terrapins, and tortoises. Chelonians first appeared in the Triassic period, about 200 million years ago, and have changed little since. Their bodies are enclosed in a shell that overlaps a bony carapace above and a plastron below. Some chelonians have a soft or leathery shell: all lack teeth and have a horny beak.
Related category• ZOOLOGY
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