Seismosaurus, now recognized as a species of Diplodocus, was widely rumored to be included as a "hidden" or "secret" animal in Carnivores, along with Brachiosaurus, with the claim that one or both animals could be unlocked after earning 10,000 points. It was often suggested to be invulnerable to anything but the X-Bow, and that its only
vulnerable spot was its eye, which was a seventh the size of the Tyrannosaurus' eye. It was also hinted to be carnivorous, or at least dangerous.
In reality, while either Seismosaurus or Brachiosaurus, or both, may have been planned for inclusion in Carnivores (and, indeed, Brachiosaurus was included in the sequel, Carnivores 2), neither animal is actually in the game, and there are no mentions of either of them in any of the game's files.