Hylonomus

Hylonomus ( /haɪˈlɒnəməs/; hylo- "forest" + nomos "dweller") was a very early reptile. It lived 312 million years ago during the Late Carboniferous period. It is the earliest unquestionable reptile (Westlothiana is older, but in fact it may have been an amphibian, and Casineria is rather fragmentary).