Apatosaurus was a sauropod that lived during the late Jurassic period. Like most sauropods, it was an herbivore that moved about on four legs, with a long craning neck and protruding tail for balance. It is believed that Apatosaurus held its head upright for grazing, more like Brachiosaurus, and not cast forward like Diplodocus.
For a long time, people used the term Brontosaurus to refer to the Apatosaurus, due to a long feud between the paleontologist-adventurers Cope and Marsh. Eventually it was decided that Marsh’s discovery took precedence, and that Apatosaurus was indeed the correct name for the genus. However, in 2015 it was resolved that Brontosaurus was a legitimate genus of its own!