Gerobatrachus hotteni (Anderson et al. 2008) Early Permian ~300 mya, ~10 cm in length is our best candidate for a common ancestor to all living frogs and salamanders. Derived from a sister to Doleserpeton, Gerobatrachus phylogenetically preceded Triadobatrachus in the lineage of frogs.
Distinct from Doleserpeton, the skull of Gerobatrachaus was wider and flatter with orbits that opened almost completely dorsally. The naris was larger. The naris was wider than long. The lacrimal completed the entire posterior border of the naris. The intertemporal was not fused to the supratemporal. The parietal opening was much larger on a much smaller pair of parietals.
The presacral vertebral number was reduced to 17. Dorsal ribs were not present on the three lumbar vertebrae. The caudal series was shorter.
The humerus was longer and longer than the femur. The pubis and ischium were much shorter. The ilium was not as tall. The robust foot was longer than the femur + tibia. Pedal 2.1 wasreduced to a disc.