Eoherpeton watsoni (Panchen 1975) Visean, Middle Mississippian ~330 mya, 1 m in length, was 8 million years older than its sister, Proterogyrinus. Both were derived from a sister to Ichthyostega and both phylogenetically preceded Seymouria and Silvanerpeton.
Distinct from Proterogyrinus, the skull of Eoherpeton had relatively a larger naris (nostril) set higher on the skull. The orbit was more circular. The maxilla contacted the quadratojugal, a primitive trait. The otic notch (embayment at the back of the skull) was greatly reduced. The teeth were larger and fewer in number.
The rest of the skeleton is poorly known, but the pelvis was deeper, as in Ichthyostega.
A reptilomorph family tree is here. A more complete family tree of the Reptilia and their ancestors is here.