Apatosaurus was a sauropod dinosaur that lived during the Late Jurassic Period (about 152 million years ago) in what is now western North America. It was one of the largest terrestrial animals to have ever existed, measuring at least 70 feet in length and weighing about 20 tons.
History
Apatosaurus has had a confusing history. The first skeletons were found all mixed up with the bones of two other species of large sauropods called Diplodocus and Camarasaurus, and when paleontologists first tried to put the skeleton of Apatosaurus together, they mistakenly put the skull of Camarasaurus on the end of the neck. So, even though most of the skeleton of Apatosaurs looked a lot like Diplodocus, the skull did not, and no one could figure out what other dinosaurs Apatosaurus was related to.
At one time, it was thought that Apatosaurus and Brontosaurus, another sauropod from the same place, were really the same dinosaur that had accidentally been given two names. A recent study has shown that although Apatosaurus and Brontosaurus are very similar, they are actually two different dinosaurs.