When did the earliest known reptiles live?

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A painted turtle (Chrysemys picta) with a dark shell and red and yellow markings rests on a rock near water, surrounded by green aquatic plants. — reptile Painted turtle (*Chrysemys picta*).

The earliest known reptiles, such as Hylonomus and Paleothyris, lived during the Late Carboniferous Period. These small, lizardlike animals were classified as Eureptilia (true reptiles) and inhabited forested environments in what is now North America.1