Apatosaurus

About 21 to 23 metres (69 to 75 feet) long and weighed 16 to 22 tonnes (18 to 24 short tons). Some specimens may have been even larger, up to 30 metres (98 feet) long and 33 tonnes (36 short tons).124

It ate plants like ferns, conifers, and other leaves. It swallowed them whole and used stones in its stomach to help digest the tough plant material.15

It lived about 152 to 145 million years ago, during the Late Jurassic Period.14

Fossils have been found in the United States, in states like Colorado, Wyoming, Utah, Oklahoma, and New Mexico.14

For many years scientists thought they were the same, but a 2015 study says they are separate, closely related dinosaurs. Not all experts agree, though.124

Young Apatosaurus grew very quickly and reached full adult size in about 10 years.1

Yes, it had a long, whiplike tail that it might have used like a whip to defend itself or make loud noises.14

Yes, Apatosaurus was much bigger. It was about 21 to 23 metres long and weighed up to 22 tonnes, while T. rex was about 12 metres long and weighed around 8 tonnes.12

Yes, they lived alongside each other in the Late Jurassic. Allosaurus was a predator that may have attacked Apatosaurus, but Apatosaurus's huge size helped protect it.15

Its name means 'deceptive lizard' in Greek. The scientist who named it, Othniel Charles Marsh, thought some of its bones were confusing and looked like those of a marine reptile.15