Hylonomus (/haɪˈlɒnəməs/; hylo- "forest" + nomos "dweller")[2] is an extinct genus of reptile that lived 318 million years ago during the Bashkirian stage of the Late Carboniferous.

It is the earliest known crown group amniote and the oldest known unquestionable reptile, with the only known species being Hylonomus lyelli.

In 1966, Robert L. Carroll suggested that H. latidens is synonymous with the type species H. lyelli and that H. multidens belongs to a different genus of 'microsaur' which he named as Novascoticus.

[12] Fossilized footprints found in New Brunswick have been attributed to Hylonomus, at an estimated age of 315 million years.

It is supposed that, after harsh weather, the club mosses would crash down, with the stumps eventually rotting and hollowing out.