(order Cotylosauria, suborder Captorhinomorpha)
What is probably the oldest-known reptile, first found in fossilized tree stumps in the Coal Measures (lower Pennsylvanian, see Carboniferous) 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.
Subjects: Earth Sciences and Geography — Zoology and Animal Sciences.