Why Is It Different?

The list of differences between Apatosaurus and Brontosaurus are actually alarmingly small. That is the reason, of course, that the two were made synonymous in 1903. Those differences that have been discussed as differing enough to cause the second separation of the taxa are still just as slight. The single character that the PeerJ flow chart makes a large deal out of is the shape of the bifurcation of the neural spines on the vertebrae. The Brontosaurus neural spines appear to have a sharper angle of bifurcation and a shorter vertebra as a whole. The Apatosaurus vertebrae are less acute in their neural spine angles and appear larger and flatter as a result. The heads of the two dinosaurs are believed to be extremely similar, perhaps identical. Their pelves have no significant differences either when viewed as a whole; smaller differences may exist on the individual bones of the pelvis of course. Those that read the paper yesterday are aware of the evidence that was used to describe the split between the two, so going in depth here should not be necessary.