Apatosaurus was third heaviest dinosaur. Only Argentinosaurus and Antarctosaurus were even heavier. Apatosaurus weighed 25 to 73 tons. It belonged to the apatosaurinae which includes Brontosaaurus. Once Apatosaurus's skull was confused with that of Brachiosaurus and Camarasaurus. It was compared with the model of Giraffatitan and Dreadnoughtus a large type of sauropod.
Species of Apatosaurus included A.ajax, and A.louisae. Ther was once a type of specie known as Apatosaurus alenquerensis but it is now based on Lourinhasaurus a close relative to Abrosaurus and Camarasaurus. Also A.yahnahpin is actually based on Brontosaurus and not Apatosaurus.
Apatosaurus lived in USA with other sauropods such as Brachiosaurus, Brontosaurus, Diplodocus and Seismosaurus which is now considered to be a Diplodocus. It also lived with it's predators such as Allosaurus,and Ceratosaurus. Smaller plant eaters such as Stegosaurus and Alcovasaurus . There were also ornithopods in the area such as Camptosaurus .