Real Seismosaurus were immense North American sauropods that lived during the Jurassic period. Seismosaurus was once believed to be the largest dinosaur of all time, and indeed one of the largest animals to ever live, at a length of 54 metres long. However more modern estimates show it to be 34-36. This is still a record length, longer than any other animal. Weight estimates range from 40-80 tonnes. Seismosaurus is now thought to be another species of Diplodocus .