Created from the ancient marine reptile known as Cryptoclidus, these kaiju were made larger, given skull-like face features and front limbs. It is unknown how many of these creatures were made, but there were at least three of them. Two were killed by Zilla while they guarded the Tachyon's ship, the Leviathan. The other appeared later during the Monster Wars saga, in which it was a major part of the alien's invasion force. The creature was used to attack Hong Kong. When the aliens lost control of the mutations, it was killed by the Alien capital ship.

Many speculate that Cryptocleidus is the American counterpart of Titanosaurus.