"They are from a very ancient group called Cryptobranchidae that are known to have existed for around 160 million years-way before dinosaurs walked the Earth.    From Wordnik.com.  [Conservation International - Feature Articles] Reference

It forms, in fact, a distinct genus of Cryptobranchidae, which.    From Wordnik.com.  [Popular Science Monthly Oct, Nov, Dec, 1915 — Volume 86] Reference

Several animal taxa also show unique affinities with East Asian relatives, including copperheads (Agkistrodon spp.), hellbender salamanders (Cryptobranchidae family), some land snails, and paddlefish (Polyodon spathula).    From Wordnik.com.  [Appalachian-Blue Ridge forests] Reference