Coelostegus prothales (Carroll and Baird 1972) Late Pennsylvanian ~310 mya, ~15 cnm snout to vent length, was derived from a sister to Paleothyris, was a sister to Hylonomus and both phylogenetically preceded Protorothyris.
Distinct from Paleothyris, the skull of Coelostegus was little changed overall. The frontals had posterior processes. Here the supratemporals were angled down. The maxilla was deeper. The posterior rim of the jugal was a vertical suture.
Overall the vertebrae and ribs were much more robust and the cervicals were slightly larger than the dorsals. The vertebrae were taller than long and the neural spines were taller than each centrum.
The rest is little different or unknown.