The Brontosaurus, a name that conjures images of immense size and a long, sweeping tail, remains one of the most widely recognized dinosaurs in popular culture. Its presence graces everything from children’s books to classic films, cementing its status as the quintessential “thunder lizard.” This iconic image has persisted for generations, even through periods of scientific debate regarding its very existence as a distinct animal.
A Dinosaur Reclaimed
The history of the Brontosaurus is a testament to the dynamic nature of scientific understanding. American paleontologist Othniel Charles Marsh first described Brontosaurus excelsus in 1879, based on a partial skeleton discovered in Como Bluff, Wyoming. Just two years prior, Marsh had named Apatosaurus ajax from a fossil found in Colorado, setting the stage for a century-long taxonomic puzzle.
The controversy deepened in 1903 when paleontologist Elmer Riggs concluded that the Brontosaurus skeleton was identical to Apatosaurus, suggesting it was a mature specimen of the same genus. Following the established rules of scientific naming, which prioritize the earlier given name, Brontosaurus was reclassified as Apatosaurus excelsus, and the name Brontosaurus was largely considered invalid for over a hundred years. Despite this scientific consensus, the evocative name “Brontosaurus” persisted in public consciousness and popular media.
A significant shift occurred in 2015 when a comprehensive study, led by Emanuel Tschopp, Octavio Mateus, and Roger Benson, re-examined numerous sauropod specimens. This extensive analysis revealed enough consistent differences between Brontosaurus and Apatosaurus to warrant separate genus classification. The research highlighted subtle but consistent distinctions, such as Brontosaurus’s neck being more high than wide, compared to Apatosaurus’s notably wider neck. This landmark study led to the reinstatement of Brontosaurus as a valid genus, demonstrating how new data and analytical methods can reshape long-held scientific classifications.
Physical Traits and Behavior
The Brontosaurus was a colossal quadrupedal sauropod characterized by its immense proportions. The largest species, B. excelsus, could reach lengths of 21 to 23 meters (69 to 75 feet) from head to tail and weighed an estimated 15 to 20 metric tons (17 to 22 short tons). Its robust body was supported by four stout, pillar-like legs, with its hind limbs typically slightly longer than its forelimbs.
A defining feature of the Brontosaurus was its exceptionally long neck, balanced by an equally long, whip-like tail. The neck vertebrae were notably strong and heavily built, contrasting with the more lightly built necks of relatives like Diplodocus. This structure would have helped support its considerable length and allowed it to reach high foliage.
Brontosaurus, like many other large sauropods, moved at a slow pace, with trackways indicating an average range of 20–40 kilometers (10–25 miles) per day. The discovery of fossilized footprints from multiple sauropods moving in the same direction suggests that herd living was common among these large herbivores. Living in groups would have offered benefits such as protection from predators and improved efficiency in finding abundant food sources.
Ancient Environment and Diet
Brontosaurus roamed North America during the Late Jurassic Period, 156 to 146 million years ago. Its fossil remains are predominantly found within the Morrison Formation, a geological formation spanning across the western United States. This formation preserves a snapshot of an ancient landscape characterized by meandering rivers, lush floodplains, and seasonal lakes. The environment was warm and humid, supporting a diverse array of plant life.
As a herbivorous sauropod, Brontosaurus relied entirely on plant matter for sustenance. Its diet likely consisted of abundant vegetation such as ferns, cycads, ginkos, horsetails, and conifers, which were prevalent in the Late Jurassic environment. The long neck of the Brontosaurus was a key adaptation, enabling it to browse on foliage high in trees.
The Brontosaurus possessed small, peg-like or spatulate teeth, which were suitable for stripping leaves from branches but not for extensive chewing. To aid in digestion, it is believed that Brontosaurus, similar to other sauropods, swallowed gastroliths or “stomach stones.” These stones would have helped to grind up the tough plant material in its stomach, maximizing nutrient absorption from its large intake of vegetation. Brontosaurus likely consumed over 600 kilograms (more than 1320 pounds) of plants daily, spending a significant portion of their day feeding.