For many, the names Apatosaurus and Brontosaurus evoke images of towering, long-necked dinosaurs, often leading to a natural question: are they the same animal? This long-standing confusion has roots in over a century of paleontological discoveries and re-evaluations. While these two sauropods share many characteristics, modern scientific understanding has clarified their distinct identities.
The Original Naming of Apatosaurus
Othniel Charles Marsh, a prominent paleontologist during the late 19th century’s “Bone Wars,” described and named the first-known species of Apatosaurus, Apatosaurus ajax, in 1877. This initial discovery was based on incomplete fossil material unearthed from the Morrison Formation in Colorado.
Marsh identified this find as a large sauropod, a group of herbivorous dinosaurs with long necks, tails, and four sturdy legs. The name Apatosaurus translates to “deceptive lizard,” referencing features of its bones that initially seemed similar to marine reptiles. This early classification laid the groundwork for understanding these creatures.
The Brontosaurus Controversy
Just two years later, in 1879, Othniel Charles Marsh named another large sauropod, Brontosaurus excelsus, from a more complete skeleton found in Como Bluff, Wyoming. The name Brontosaurus, meaning “thunder lizard,” quickly captured public imagination due to its impressive size. For decades, both names coexisted, but their relationship was destined for re-evaluation.
The turning point arrived in 1903 when paleontologist Elmer Riggs conducted a detailed comparison of the Apatosaurus and Brontosaurus specimens. Riggs determined that Brontosaurus excelsus was so anatomically similar to Marsh’s earlier discovery, Apatosaurus ajax, that it did not warrant its own genus. Consequently, Brontosaurus was reclassified as a junior synonym of Apatosaurus (Apatosaurus excelsus), as the older name takes precedence. For over a century, this consensus meant Brontosaurus was considered a species within the Apatosaurus genus, leading to widespread public belief that the two were identical.
Brontosaurus’s Return to the Spotlight
Despite the scientific reclassification, the name Brontosaurus remained popular in culture, often appearing in books and media. The scientific community, however, largely adhered to the synonymy until a significant re-evaluation in 2015. A comprehensive study by Emanuel Tschopp, Octávio Mateus, and Roger Benson meticulously analyzed numerous sauropod specimens, including those historically assigned to Apatosaurus and Brontosaurus.
Their five-year research, comparing 477 anatomical features across 81 fossil skeletons, revealed consistent morphological differences. These distinctions were substantial enough to justify re-establishing Brontosaurus as a distinct, valid genus, separate from Apatosaurus. This landmark study officially brought the “thunder lizard” back into scientific recognition as its own unique dinosaur, though closely related to Apatosaurus.
Key Differences Between the Two
With Brontosaurus now recognized as distinct, paleontologists can point to specific morphological features that differentiate it from Apatosaurus. While both are robust, long-necked sauropods within the family Diplodocidae, subtle yet consistent anatomical variations exist. One notable difference lies in the structure of their neck vertebrae.
Apatosaurus had a wider, more robust neck than Brontosaurus. Conversely, Brontosaurus had a taller, less robust neck, contributing to a lighter-built appearance despite its massive size. Differences also extend to the neural spines on their dorsal (back) vertebrae, with Apatosaurus having spines that formed larger curves than Brontosaurus. These detailed skeletal differences provide the evidence paleontologists use to distinguish between these two separate dinosaur genera.