FAS Astronomers Blog, Volume 31, Number 14b. When I was growing up, Brontosaurus was almost as famous as T. rex. However, Othniel Marsh made a mistake (maybe). In 1877, he discovered a dinosaur, which he named Apatosaurus ajax (Marsh 1877). Two years later, in 1879, he discovered another similar dinosaur, which he named Brontosaurus excelsus…