Gephyrostegus watsoni (Brough and Brough 1967 was originally named Diplovertebron punctatum (Watson 1926) but reassigned to Gephyostegus bohemicus by Carroll (1970) despite the size difference, who thought G. watsoni was a juvenile. Derived from a sister to Eldeceeon, a sister to G. watsoni (which needs a new generic name) was basal to the larger Solenodonsaurus and the smaller Brouffia, Casineria and Westlothiana. G. watsoni was a contemporary of G. bohemicus, Upper Carboniferous (~310 mya), so it, too, was a late survivor.
Overall smaller and distinct from Eldeceeon, the skull of G. watsoni had a shorter rostrum, larger orbit and greater quadrate lean. The dorsal vertebrae formed a hump and had elongate spines. The hind limbs were much longer than the forelimbs. The tail is incomplete, but appears to have been short and deep.
Seven sphere shapes were preserved alongside this specimen. They may be the most primitive amniote eggs known.