Othniel Charles Marsh, a Professor of Paleontology at Yale University, described and named an incomplete (and juvenile) skeleton of Apatosaurus ajax in 1877.
Two years later, Marsh announced the discovery of a larger and more complete specimen at Como Bluff Wyoming—which, because of discrepancies including the size difference, Marsh incorrectly identified as belonging to an entirely new genus and species.
He dubbed the new species Brontosaurus excelsus, meaning “thunder lizard”, from the Greek brontē/βροντη meaning ‘thunder’ and sauros/σαυρος meaning ‘lizard’ and from the Latin excelsus, “highest, sublime”, referring to the greater number of sacral vertebrae than in any other genus of sauropod known at the time. (Wikipedia)
Marsh’s head swelled to the size of a juvenile apatosaurus when he unearthed the now defunct brontosaurus.
Here I am as a dinosaur in case you were wondering: