New Mexico Museum of Natural History and Science

Paleontologists distinguish the two main groups of dinosaurs by hip structure. They refer to the pelvis of Seismosaurus as "lizzard-hipped" or saurischian (sore-ISH-ee-an) because it resembles the pelvis of a modern lizard. In contrast, paleontologists term the pelvis of Stegosaurus "bird-hipped" or orinthischian (or-nith-ISH-ee-an) because it somewhat resembles the pelvis of a living bird.

Paleontologists compared the hip and back bones of Seismosaurus to the complete skeleton of the closely-related dinosaur Diplodocus to reconstruct the skeleton of Seismosaurus exhibited here.