I took another look at this pair of very basal amniote taxa recently and found they nested together. The resemblance actually grows on you as you examine the details. The shallow maxilla, the concave dorsal mandible. Of course, one is much larger than the other. As sisters one gives clues to the other’s missing parts, like the cranium of Cephalerpeton and the post-crania of Reiszorhinus.
Wiki lists Late Carboniferous Cephalerpeton as a protorthyrid and Early Permian Reiszorhinus as a captorhinid.