Apatosaurus

Apatosaurus was a large sauropod dinosaur. It lived around 150 million years ago in the Late Jurassic Period, in an area that is now North America.

Like all sauropods, Apatosaurus ate plants.

Young Apatosaurus individuals grew up quickly. They took around 10 years to reach full adult size.

Apatosaurus lived alongside Stegosaurus, Diplodocus and Allosaurus.

Their fossils were found in the Morrison Formation, a sequence of rocks that covers a huge area spanning several US states, including Wyoming, Colorado and Montana. Many dinosaurs have been discovered there.

During the Late Jurassic the environment was semi-arid, with forests, rivers and floodplains. There were distinct wet and dry seasons.

Apatosaurus had a long, narrow tail that it might have used as a whip.

The animal's huge size would also have helped to protect it from smaller predators, which may have found Apatosaurus too big to take on. Living in herds gave extra protection.

The name Apatosaurus comes from Greek words meaning 'deceptive lizard'. The scientist who named this dinosaur, Othniel Charles Marsh, felt that some of the fossil bones were confusing to identify. They seemed to resemble the bones of a sea reptile.

For more than 100 years, most scientists stopped using the well-known dinosaur name Brontosaurus. They thought that Brontosaurus and Apatosaurus fossils were the same thing.

But based on a study done in 2015, experts now think that the two dinosaurs are separate after all, although they are closely related.

Apatosaurus went extinct 145 million years ago, at the end of the Jurassic Period.