It is the largest salamander known to have ever existed, with a maximum estimated length of 2.3 m (7 ft 7 in).

[1] In 1917, Harold Cook named the new genus and species Plicagnathus matthewi for a dentary from Nebraska, specifically from the unit known as the "lower Snake Creek beds",[2] which was later renamed as the Olcott Formation.

[6] The species was named in honor of William Diller Matthew, who first identified the specimen.

[2] In 1963, Joseph Tihen and Charles Chantell named the new species Cryptobranchus mccalli for two maxillae from the Valentine Formation of Nebraska.

[7] Naylor estimated a length of 2.3 m (7 ft 7 in) using two vertebrae from the Wood Mountain Formation of Saskatchewan.