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Hylonomus lyelli Ancient, probably the oldest-known, reptile. Hylonomus is a stem reptile and a member of the Captorhinomorpha. It was first found in fossilized tree stumps in the Coal Measures of Nova Scotia. The skull roof of this species was fully ossified and there were no openings behind the eye sockets. Hylonomus measured some 25 cm and possessed a long tail.