The rise and fall of " Brontosaurus" is
By the time the Yale skull was created, the debate over the skull shape of Brontosaurus had already been going on for several decades: There was an inkling that some of the long, low skulls attributed to Diplodocus from Utah's Dinosaur National Monument really belonged to Brontosaurus, but many restorations presented the animal with a shorter, boxy skull like that of Camarasaurus. O.C. Marsh, the famous 19th-century paleontologist and founder of the Peabody Museum, had been the architect of the latter interpretation, basing his illustrations of the dinosaur's head on skull materials that were later found to belong to Camarasaurus and Brachiosaurus.
Marsh was not very well-liked by the crop of paleontologists that followed him - what better way to secure your own place as a leading paleontologist than to show that Marsh was wrong? - but in this case many other authorities followed his lead. For the Yale reconstruction, the preparator based the skull shape off of a bit of lower jaw from Wyoming designated YPM 1911, which appeared to confirm that Brontosaurus had a Camarasaurus-like head. The end result, mostly created out of plaster, was a squared-off head with protruding jaws and a nasal opening that pushed up the skull to give the dinosaur a rather snooty air. Completed in the 1920s, this reconstruction was mounted on the museum's mighty sauropod in 1931 and was key reference the artist Rudolph Zallinger used in creating the great "Age of Reptiles" mural that still provides the backdrop to the museum's dinosaur hall.
As museums revamp their exhibition space, the image of dinosaurs I grew up with is slowly being replaced. This is a good thing, but I also cherish the fact that paleontologists are aware of their own history. Our science does not proceed simply by collecting new evidence. Paleontologists must also reexamine old ideas and previously-discovered fossils to glean new insights, and I am glad to see that history often has a prominent place in many fossil halls. The stupid, swamp-bound Brontosaurus I was introduced to as a child never existed, but we can still learn something by reminding ourselves how and why that imagery was replaced.