Brontosaurus

Phylogeny: Dinosauria > Saurischia > Sauropodomorpha > Plateosauria > Massopoda > Sauropodiformes > Sauropoda > Gravisauria > Eusauropoda > Neosauropoda > Diplodocoidea > Diplodocidae > Apatosaurinae

Overview: For much of the past century, if a scientifically-based list of dinosaurs were made, this incredibly famous genus probably wouldn’t have been included. It was first established as a genus in 1879 by the renowned American paleontologist Othniel C. Marsh. The creature’s name, meaning “thunder lizard”, is meant to invoke its impressive size. Indeed, it was one of the largest dinosaurs known at that time. Two years prior, Marsh had described a very similar dinosaur, which he named Apatosaurus. Upon studying Brontosaurus, he concluded the two were distinct taxa. In 1903, a far more detailed re-description of both dinosaurs was published by Elmer S. Riggs, in the same year he described the genus Brachiosaurus. Riggs found that Brontosaurus and Apatosaurus were far too similar to be distinct genera, though he recognized them as separate on the specific (species) level. He officially reassigned the species Brontosaurus excelsus and Brontosaurus parvus to the genus Apatosaurus. Apatosaurus, being described first, had priority if they were the same genus. Most paleontologists would agree with Riggs, so the name Brontosaurus fell out of official use.

It would be a different story in popular culture, however. Two years later, in 1905, a fully mounted skeleton would be unveiled in the American Museum of Natural History, labeled as Brontosaurus. It would cause the name to spread among the general public, eventually to a point that most people came to refer to all sauropods as “brontosaurs”. The skeleton was also mounted with an incorrect skull, that of a Camarasaurus, but contrary to popular myth, this had nothing to do with why the generic name was changed. Eventually, all mounted skeletons of all referred Apatosaurus species were labeled as such. Brontosaurus being a junior synonym of Apatosaurus would remain the popular consensus among researchers until the 2010’s. In 2015, a study was published that found the species originally referred to Brontosaurus, along with one since referred to Apatosaurus (now B. yahnahpin), had enough differences to warrant them being in a separate genus. Not all agreed with this conclusion, but it has since found quite a bit of support among researchers.

Even if Brontosaurus was distinct from Apatosaurus, the two animals were clearly closely related, bearing most superficial features in common. Both belonged to the sauropod family Diplodocidae, a part of the larger neosauropod superfamily Diplodocoidea. This made them related to genera like Barosaurus and Diplodocus. Brontosaurus and Apatosaurus, however, were a bit more basal, belonging to a subfamily called the Apatosaurinae. Apatosaurine diplodocids tended to be bulkier, with thicker necks than those of the diplodocine diplodocids. Between the two, Apatosaurus was the more heavily built genus, with Brontosaurus typically being a bit smaller. Still, it was one of the largest animals in its local environment. Brontosaurus and Apatosaurus are both known from the Late Jurassic-aged Morrison Formation in the western United States. Some Brontosaurus species are known from deeper layers of the Morrison than those of Apatosaurus. These animals lived in a semi-arid, seasonal environment, alongside many other sauropods, stegosaurs, ornithopods and a few large theropods like Allosaurus, Ceratosaurus and Torvosaurus.