Early size estimates suggested this dinosaur was far longer than recent revisions have shown. Seismosaurus has since been reclassified as a species of Diplodocus (D. hallorum), and may in fact be the same as a previously named species, D. longus.
Other Info: In episode 19, it defeated Terry, Spiny, and Tank, also saving Dr. Owen after he fell off the Statue of Liberty. It faced off against Supersaurus in episode 20. The TCG made it into a Water Dinosaur, and it is featured on a TCG-only Normal Move, Mega Backup.