Spinoaequalis schultzei (deBraga and Reisz 1995) Late Carboniferous ~306 mya, ~30 cm in length, was originally considered a basal diapsid close to Petrolacosaurus and Araeoscelis, but with a deep, sculling tail. Here that nesting is confirmed with a close relationships to Eudibamus. More importantly, Spinoaequalis nests at the base of the marine younginiformes, like Galesphyrus and the terrestrial younginformes, like Youngina SAM K7710 (see links below). The deep tail, however, is an autapomorphy of Spinoaeaqualis not expressed in descendant taxa, except, perhaps and separated by several nodes, Hovasaurus.
Distinct from Eudibamus, the rostrum was longer, like that of Petrolacosaurus. A small upper temporal fenestra was retained. The teeth were longer. The torso was longer with a longer lumbar area. The neural spines of the tail were much taller. The scapula was smaller and the coracoid was not fused to it. Like Eudibamus, finger 5 is unknown. Digit 4 was several times longer than the metatarsal. Metatarsal 4 remained the widest proximally. The metatarsals were more symmetrical.