Seymouria baylorensis (Broili 1904, Laurin 1996, Klembara J et al. 2007; Early Permian ~275 mya, 0.6-1 m in length) was so adapted to life on land that early workers considered it a reptile. Derived from a sister to Eldeceeon, Seymouria phylogenetically preceded Utegenia and Silvanerpeton and was a sister to Kotlassia.
Distinct from Eoherpeton, the skull of Seymouria further raised the naris and directed it anteriorly. The maxilla was deeper and carried longer teeth. The jugal separated the maxilla from the quadratojugal. The parietal plate was longer and the otic notch was deeper. The medial skull bones were wider creating a skull with steeper sides.
Distinct from Proterogyrinus, the neural spines were shorter and angled posteriorly. The dorsal ribs flared widely creating a wide torso. The tail was much reduced although it still included a large number of vertebrae. It was not as useful for aquatic propulsion.
The cleithrum was reduced and the clavicle elongated. The ulna included an olecranon process (elbow) and the carpus was full ossified. The digits were shotrer, unlike those of Silvanerpeton and basal reptiles.
The dorsal process of the ilium was much larger than the posterior process, unlike Silvanerpeton and reptiles. The fibula was much narrower than the tibia. The pedal digits were narrower than the manual digits.
A reptilomorph family tree is here. A more complete family tree of the Reptilia and their ancestors is here.