The Cryptobranchidae are a family of fully aquatic salamanders commonly known as the giant salamanders. They include the largest living amphibians. The family is native to China, Japan, and the eastern United States. They constitute one of two living families—the other being the Asiatic salamanders belonging to the family Hynobiidae—within the Cryptobranchoidea, one of two main divisions of living salamanders.
The largest species are in the genus Andrias, native to east Asia. The South China giant salamander (Andrias sligoi), can reach a length of . The Japanese giant salamander (Andrias japonicus) reaches up to in length, feeds at night on fish and crustaceans, and has been known to live for more than 50 years in captivity.
The hellbender (Cryptobranchus alleganiensis) inhabits the eastern United States and is the only member of the genus Cryptobranchus.
Taxonomy
The family name is from the Ancient Greek krypto ("hidden"), and branch ("gill"), which refer to how the members absorb oxygen through capillaries of their side-frills, which function as gills.
Clade Pancryptobrancha (Cryptobranchidae + Ukrainurus) Genus †Ukrainurus Ukraine, Miocene †Ukrainurus hypsognathus Genus †Chunerpeton? China, Middle Jurassic †Chunerpeton tianyiensis Family Cryptobranchidae Genus Cryptobranchus (hellbenders) †Cryptobranchus saskatchewanensis? Ravenscrag Formation, Canada, Paleocene Cryptobranchus alleganiensis (hellbender) Genus Andrias (Asian giant salamanders; sometimes classified among the Cryptobranchus) Andrias davidianus (Chinese giant salamander) – (Simplified Chinese: ; pinyin: ) (may actually be a species complex of 5 different species) Andrias sligoi (South China giant salamander) Andrias japonicus (Japanese giant salamander) – () Andrias jiangxiensis (Jiangxi giant salamander) †Andrias matthewi North America, Miocene †Andrias scheuchzeri Europe, Oligocene-Pliocene Genus †Eoscapherpeton Central Asia, Late Cretaceous (Cenomanian-Campanian) Genus †Aviturus Mongolia, Paleocene †Aviturus exsecratus Genus †Ulanurus Mongolia, Paleocene †Ulanurus fractus Genus †Zaissanurus Kazakhstan, Oligocene †Zaissanurus beliajevae
Fossil record
Extant species in the family Cryptobranchidae are the modern-day members of a lineage that extends back tens of millions of years. The oldest known fossils of cryptobranchoids are known from the Middle Jurassic of China. Chunerpeton from the Middle Jurassic of China has been suggested to represent the oldest known cryptobranchid. However, some studies have found it to be a more basal cryptobranchoid not more closely related to Cryptobranchidae than to Hynobiidae. The next oldest cryptobranchid is Eoscapherpeton, known from numerous Late Cretaceous deposits in Central Asia, which is suggested to represent a stem-group to modern cryptobranchids. Modern crown group representatives appear during the Paleocene.
As the fossil record for the Cryptobranchidae shows an Asian origin for the family, how these salamanders made it to the eastern US has been a point of scientific interest. Research has indicated a dispersal via land bridge, with waves of adaptive radiation seeming to have swept the Americas from north to south.
In 1726, the Swiss physician Johann Jakob Scheuchzer described a fossil as Homo diluvii testis (Latin: Evidence of a diluvian human), believing it to be the remains of a human being who drowned in the biblical flood. The Teylers Museum in Haarlem, Netherlands, bought the fossil in 1802, where it is still exhibited. In 1812, the fossil was examined by Georges Cuvier, who recognized that it was not human. After being identified as a salamander, it was renamed Salamandra scheuchzeri by Holl in 1831. The genus Andrias was coined six years later by Tschudi. In doing so, both the genus, Andrias (which means "image of man"), and the specific name, scheuchzeri, ended up honouring Scheuchzer and his beliefs. It and the extant A. davidianus cannot be mutually distinguished, and the latter, only described in 1871, is therefore sometimes considered a synonym of the former.
Description
Cryptobranchids are large salamanders, with large folds of skin along their flanks. These help increase the animals' surface area, allowing them to absorb more oxygen from the water. They have four toes on the fore limbs, and five on the hind limbs. They have paedomorphic traits, meaning their metamorphosis from the larval stage is incomplete, so the adults retain gill slits (although they also have lungs), and lack eyelids. They have a stout body with a heavy, laterally compressed tail. They have bad eyesight. They can reach a length of , though most are considerably smaller today.