The Family Ascaphidae comprises the tailed frogs, a small and primitive group of frogs found in cold, fast-flowing streams of the Pacific Northwest of North America. They are notable for the male’s internal copulatory organ (tail-like extension), which allows internal fertilization—a rare trait among frogs. Ascaphids are adapted to turbulent stream environments, with flattened bodies, strong limbs, and specialized tadpoles that cling to rocks using suction-like mouthparts. As an ancient lineage, they provide important insights into the evolution of reproduction and adaptation in amphibians.