A new paper has resurrected Brontosaurus as a valid taxon. The cladistic study of diplodocid dinosaurs concluded that there were substantial differences between Apatosaurus and Brontosaurus: the former is even more robust and has a distinctly thicker neck. News coverage: Nature, Scientific American, Brian Switek at Smithsonian.
O. C. Marsh named Apatosaurus ajax in 1877 and Brontosaurus excelsus two years later. Paleontologists later concluded that ajax and excelsus were just two different species of the same genus. The rules of scientific nomenclature generally hold that the senior name takes precedence. Since Apatosaurus was named first, “Brontosaurus” had to give way. (This is, by the way, what will happen with Triceratops and Torosaurus, if the proposal that Torosaurus is the mature form of Triceratops gains wide acceptance: Triceratops came first.)
It’s important not to get too excited over this sort of thing. It happens all the time in the biological sciences (see Tom Spears’s piece in the Ottawa Citizen). Herpetologists have been on a reclassification rampage for the last couple of decades; it’s no different with dinosaurs.
As a child who read every damn dinosaur book in the library, no matter how old, I was mightily confused by the inconsistent naming: nomena dubia were in every book. Anatosaurus and Trachodon have since been folded into Edmontosaurus, Stenonchyosaurus has been reclassified as the previously mysterious Troodon, and Brachiosaurus has been split in two, so that now some mounted skeletons are a mix of Brachiosaurus altithorax and Giraffatitan brancai.
The fact that Deinonychus antirrhopus was briefly considered a species of Velociraptor is probably the reason why Velociraptor—an Asian dromaeosaurid about the size of a turkey—ended up in Jurassic Park as something way too big.
And there’s no guarantee that this study will be the last word on the subject. A decade from now someone else may produce equally convincing arguments that Apatosaurus and Brontosaurus should be combined after all. It happens all the time.