Cephalerpeton ventriamatum (Moodie 1912) Mid-Pennsylvanian ~306 mya, snout-vent length ~10 cm, is a basal lepidosauromorph. Originally described as an microsaur amphibian, Cephalerpeton had been associated with microsaurs, like Tuditanus and romeriids, like Romeria texana, but only the latter is valid.
Cephalerpeton was derived from a sister to Thuringothyris and was a sister to the much larger Reiszorhinus (shown above). Concordia and Romeria primus are sisters to these two.
Distinct from Gephyrostegus, the skull of Cephalerpeton was relatively large with a large orbit. This pattern is similar to that of tiny Gephyrostegus watsoni. A discrete intertemporal bone could have been present or absent. The quadrate leaned anteriorly. The otic notch was absent. The maxillary teeth were enormous. The mandible was concave dorsally in order to accommodate the upper teeth. The postorbital portion of the skull was shorter. The postfrontal extended over the postorbital to mid orbit. The premaxillary teeth were longest medially and the premaxilla tipped down. The palate was relatively shorter. The transverse process of the pterygoid was more developed and had a single transverse row of teeth.
The cervicals were elongated. The pleurocentra were greatly enlarged, crowding out the intercentra.
The scapula and coracoid were unfused and short. The humerus was longer, more slender and hourglass-shaped. The radius and ulna were likewise more slender and relatively longer. Of the hand only the metacarpals were preserved.
A large skull and large orbit are traits typically associated with juveniles. Tiny Cephalerpeton nests at the end of a phylogenetic series of decreasing size beginning with Proterogyrinus and continuing with Silvanerpeton and Gephyrostegus among the basal Tetrapoda.bSmaller animals generally mature faster and thus reproduce more often, although their lifespans are also typically shorter. The fact that Cephalerpeton is so much smaller than Gephyrostegus is a key factor in the origin of the Reptilia (Carroll 1970). The first eggs provided with an amniotic membrane were probably small and laid by small adult females who lived and laid eggs in moist leaf litter, a transitional environment that stayed humid and protected both the adult and the egg from desiccation.