Cryptocledius were aquatic long-necked reptiles, or plesiosaurs, that went extinct at the end of the Cretaceous period, in 65,000,000 B.C. However, it seems a number of the Cryptocledius somehow survived extinction.
When H.E.A.T. get out of the Tachyon ship, another Cryptocledius appears. Zilla Junior tries to evade them and eventually hits a rock formation, causing the two Cryptocledius to be crushed by the rock slide.
During the event of Monster Wars, one of the Cryptocledius survived and was spotted swimming towards Site Omega. It attacked H.E.A.T.'s boat and was tricked into fighting the Giant Bat. After the fight was broken up, both mutations traveled to Site Omega. Once the aliens began their assault, Cryptocledius attacked Hong Kong. When the alien control was severed, Cryptocledius was killed by the Tachyon ship's beams.