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.
- It's possible Cryptocledius survived the Tachyon beams, as he dived down to the depths to escape injury. This is determined as Godzilla did the same thing and survived.
- If this is true, then Cryptocledius might still be living among the depths of the ocean, or was captured and is living on Monster Island.
- Besides its oversized appearance, Cryptocledius is depicted inaccurately in the series.
- Its shown to have claws on its flippers, when it lacked them in real life.
- While its origins state it survived the KT extinction, real Cryptocledius died out 100 million years before the KT extinction. To be more accurate, the closest plesiosaur to live near the KT extinction was Elasmosaurus, a distant cousin of Cryptocledius.
- Its shown to be able to move across the land, when it couldn't do it in real life. (This is a possible reference to the third episode of Walking With Dinosaurs, where Cryptocledius were shown to hull themselves onto land for safety).
- The head of Cryptocledius is similar to that of the Skullcrawlers in Kong: Skull Island.