One of several gigantic saurischian dinosaurs recorded from the Upper Jurassic. Apatosaurus was a sauropod, a quadruped with a long neck, the total weight of which reached 30 tonnes. The name Apatosaurus is a senior synonym of Brontosaurus (i.e. it was the earlier of the two names). Animals of 22 m in length have been recorded from the Morrison Formation of N. America.