Mounted skeleton was on display at the American Museum of Natural History
Reconstruction by Charles Knight
When: Holocene (1879 to 1903)
Where: Scientific literature and museums on the east coast of the USA. Found even today in public consciousness and outdated dinosaur books.
What: Brontosaurus is perhaps the most well known of the sauropod dinosaurs. Too bad it never really existed! The history of this name and why it became so popularized starts in 1877 when the paleontologist Othniel Charles Marsh applied the name Apatosaurus to a sauropod specimen. This specimen was not very complete and mostly represented by vertebrae and a pelvis. Two years later he erected the name Brontosaurus based on an almost complete skeleton that was missing its head. Headless sauropod skeletons are fairly common, but in this case this missing head only served to make the story even more complicated.
This missing head was obviously a problem when the skeleton of Brontosaurus was mounted for display at the American Museum of Natural History. There was great debate over which head to use, which some camps wanting to use one that resembled Diplodocus but others rallied behind a Brachiosaurus type skull. This latter skull was what Marsh had envisioned in his publications on Brontosaurus, so after much heated debate a Brachiosaurus type skull was attached to the previously headless skeleton. This skeleton was unveiled to the public in 1905 to great fanfare and soon after the a few other museums around the world had their own Brontosaurus on display, with an identical head to the Yale specimen.
So the general public had a firm concept of the dinosaur Brontosaurus! It was an easy to remember and pronounce name, this is what it looked like, and hey look we even have all of these lovely reconstruction showing these great lumbering beasts in prehistoric swamps. Too bad everything was wrong. And even worse, it was KNOWN to be wrong by some workers who were shouted down by others. In 1903, two years before the specimen was mounted at Yale, a paper was published Elmer Riggs at the Field Museum of Chicago that declared that the bones known for Apatosaurus that overlapped with those of Brontosaurus showed that these two animals were the same. He concluded that Brontosaurus was not a valid name as it was two years younger than Apatosaurus. Even worse, remember the great head debate? Totally wrong. Later fossil finds have confirmed that a Diplodocus style head should have been used. These skulls are much more elongated and flatter than the high domed skull that was used for the Brontosaurus mount.
So not only is the name not valid, but the anatomy of the animal isn’t even anything that ever existed in nature! It is a chimera of different species. Also sauropods were not aquatic swamp dwellers, they were 100% terrestrial creatures.