This specimen is a tail vertebra from Seismosaurus, the longest known dinosaur. Stretched out at 110 feet (33 meters) long, Seismosaurus was a sauropod that walked on four legs, ate only plants and had an extremely long neck, large body and long tail. The only known specimen of Seismosaurus was found in rocks of the Morrison Formation that date from the Late Jurassic, about 150 million years ago.

The tail of Seismosaurus probably had 75 or more vertebrae. This vertebra would have been at the base of the animal's tail. The last few vertebrae in the tail were extremely long and thin, forming a "whip" that the dinosaur may have used to protect itself from predators.