The long-necked sauropods Apatosaurus and Brontosaurus have one of paleontology’s most tangled histories. These massive, plant-eating dinosaurs roamed the Earth during the Late Jurassic period, and for over a century, scientists debated whether they represented one genus or two. The question of whether the “deceptive lizard” and the “thunder lizard” were distinct species or the same animal has been a continuous point of debate since their initial discovery.
The History of the Mistaken Identity
The confusion began in the late 1800s during the intense period of fossil collection known as the Bone Wars. Paleontologist Othniel Charles Marsh first named Apatosaurus ajax in 1877 from a partial skeleton uncovered in Colorado. Just two years later, Marsh described a more complete, impressive specimen found in Wyoming, which he named Brontosaurus excelsus, meaning “thunder lizard”.
The stability of the name ended in 1903 when paleontologist Elmer Riggs re-examined the specimens. Riggs concluded that the differences between the two dinosaurs were too minor to justify placing them in separate genera, suggesting that Brontosaurus was merely a species within the genus Apatosaurus. Under the rules of taxonomic naming, the older name, Apatosaurus, was given priority, and the genus Brontosaurus was officially retired.
This reclassification was complicated by an error in the initial museum display of the Apatosaurus skeleton. Marsh’s original Apatosaurus specimen lacked a skull, and a skull similar to that of the sauropod Camarasaurus was mistakenly placed on the mount. This incorrect head was prominently featured on the famous “Brontosaurus” museum displays for much of the 20th century.
The Modern Taxonomic Reclassification
For more than a hundred years, the scientific consensus held that Brontosaurus was an invalid name. This long-standing view was challenged in 2015 by an exhaustive, multi-year study conducted by a team of paleontologists.
The researchers performed a detailed morphological analysis on 81 specimens from the family Diplodocidae, comparing over 477 different anatomical features across the numerous fossils. This extensive comparison allowed them to perform a detailed phylogenetic analysis to map out the evolutionary relationships between organisms.
The study concluded that the anatomical differences between the Apatosaurus specimens and the original Brontosaurus specimen were significant enough to warrant re-establishing Brontosaurus as its own distinct genus. The number of differentiating characteristics found was comparable to the distinctions commonly seen between other closely related, but separate, sauropod genera. This evidence officially restored Brontosaurus to its own taxonomic status, confirming that Marsh was correct in his initial assessment of the two animals.
Defining Features of Each Dinosaur
Now considered separate genera, Apatosaurus and Brontosaurus exhibit clear anatomical distinctions, particularly in their skeletal structure. The most notable difference lies in the cervical vertebrae, the bones that make up the neck.
Brontosaurus had a longer neck, partly due to possessing an extra cervical vertebra in some species, typically having 16 compared to the 15 found in Apatosaurus. The internal structure of the vertebrae also varied: Brontosaurus possessed cervical vertebrae with more extensive air pockets, a feature called pneumatization, which made its neck bones lighter.
In contrast, Apatosaurus was a more robustly built animal overall, especially in its neck and limb structure. Its cervical vertebrae were shorter, wider, and more heavily constructed, suggesting a thicker and stronger neck. The broader, stockier build of Apatosaurus extended to its limbs, which were thicker compared to its re-established relative.