Cryptobranchoidea

The Cryptobranchoidea are a suborder of salamanders found in Asia, European Russia, and the United States. They are known as primitive salamanders, in contrast to Salamandroidea, the advanced salamanders. It has two living subdivisions, Cryptobranchidae (Asian giant salamanders and hellbenders), and Hynobiidae, commonly known as Asian salamanders. Giant salamanders are obligate paedomorphs with partial metamorphosis, but Asiatic salamander goes through a full metamorphosis. The only known exceptions are the Longdong stream salamander, which has been documented as facultatively neotenic, and the Ezo salamander, where a now assumed extinct population from Lake Kuttarush in Hokkaido had neotenic traits like gills in adults. The oldest members of the group are known from the Middle Jurassic (Bathonian) aged Yanliao Biota of China.