Seymouriamorpha were a small but widespread group of reptiliomorphs. Many seymouriamorphs were terrestrial or semi-aquatic. However, small aquatic larvae bearing external gills were found, making them unquestionably amphibians. The adults were terrestrial. They ranged from lizard-sized creatures (30 centimeters) to crocodile-sized 150 centimeter long animals. They were reptile-like. Because seymouriamorphs are reptiliomorphs, they were the distant relatives of amniotes, or the relatives of the amniotes's ancestor. Seymouriamorphs form into three main groups, Kotlassiidae, Discosauriscidae, and Seymouriidae, a group that includes the best known genus, Seymouria. The last seymouriamorph became extinct by the end of Permian.