Protorothyris archeri (Price 1937) lived ~290 mya during the Early Permian. It was derived from a sister to Paleothyris. Sister taxa include Coelostegus, Hylonomus, Varanops, Archaeothyris and Mesenosaurus.
Compared to Paleothyris, Protorothyris had a much larger head and a deeper skull with support from a taller cervical series. The canine tooth was several times longer than the other teeth and the rostrum came to a distinct point in lateral view. The orbit (eye socket) was over a deeper jugal. The preorbital portion of the skull was longer than the postorbital portion. The nasals narrowed toward the naris. The supraoccipital was broader than the exoccipitals.
The scapulocoracoid was well ossified. The chest was deeper than the pelvis.