a·pa·to·saur / ˌapitōˈsôrəs/ (also apatosaurus / -ˈsôrəs/ ) • n. a huge herbivorous dinosaur (genus Apatosaurus, infraorder Sauropoda, order Saurischia) of the late Jurassic period, with a long neck and tail. Also called, esp. formerly, brontosaurus. DERIVATIVES: a·pa·to·sau·ri·an adj.

Apatosaurus (order Saurischia, suborder Sauropoda) One of several gigantic dinosaurs recorded from the Upper Jurassic, Apatosaurus was a quadruped with a long neck whose total weight reached 30 tonnes. The name Apatosaurus, meaning ‘deceptive lizard’ (derived from the Greek apate meaning ‘deceit’ and saura meaning ‘lizard’), is a senior synonym of Brontosaurus. Animals of 22 m in length have been recorded from the Morrison Formation of N. America.

Apatosaurus 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.

apatosaur (formerly brontosaur) Any member of the Apatosarus genus of herbivorous dinosaurs. Apatosaurs date from the Jurassic and early Cretaceous periods. They had long necks and tails. The apatosaurs' small head had eyes and nostrils on the top so that they could remain almost completely immersed in water. Length: 21m (70ft); weight: to 30 tonnes.