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 a large animal, being at least 70 feet in length, ad weighed about 20 tons, but some old adults were probably a lot bigger. Thankfully, this Apatosaurus toy is small enough to fit in your home! History: The history of Apatosaurus is confusing - The first skeleton, found in the 1870s, lacked a skull. Although some bones of its skeleton looked a lot like Diplodocus, which lived at the same time, other bones looked more like another dinosaur called Camarasaurus. This made it difficult to figure out exactly where Apatosaurus fit in with other dinosaurs. We now know that the skull of Apatosaurus looked more like Diplodocus than Camarasaurus , so we able to put Apatosaurus and Diplodocus in the same family. Scientific Name: Apatosaurus.