Brontosaurus and Brachiosaurus are two of the most recognizable long-necked dinosaurs, often appearing similar in popular culture. Despite their shared traits as large, herbivorous sauropods from the Late Jurassic period, they possessed distinct physical characteristics and different evolutionary paths. Understanding these differences clarifies why they are recognized as separate and fascinating prehistoric giants.
Introducing Each Dinosaur
Brontosaurus, meaning “thunder lizard,” was a robust sauropod that roamed North America approximately 156 to 146 million years ago during the Late Jurassic period. It featured a long neck and a whip-like tail, supported by a robust body and thick legs. This herbivore, primarily found in what is now Utah and Wyoming, could reach lengths of 69 to 75 feet and weigh between 15 to 30 tons, feeding on vegetation from the ground level to lower tree branches.
Brachiosaurus, whose name translates to “arm lizard,” lived in North America around 155 to 143 million years ago. It had a giraffe-like posture, characterized by significantly longer front limbs compared to its hind limbs. Brachiosaurus was a high-browser, using its long neck to reach foliage in tree canopies. It could measure between 59 and 72 feet long and weigh an estimated 28 to 47 metric tons.
Distinguishing Features
A primary difference between Brontosaurus and Brachiosaurus lies in their body shape and stance. Brontosaurus had a more horizontal body posture, with its neck and tail held parallel to the ground, requiring a long, whip-like tail for counterbalance. Its front legs were slightly shorter than its hind legs, contributing to this appearance. In contrast, Brachiosaurus had a distinctly upright, giraffe-like posture because its forelimbs were longer than its hindlimbs, causing its back to slope downward from the shoulders.
Their neck posture and head shapes also varied. Brachiosaurus’s neck was held more vertically, allowing it to browse foliage high in the tree canopy, potentially reaching over 30 feet above the ground. Its skull had distinctive high-set nostrils and a dome-like crest. Brontosaurus, on the other hand, held its neck in a more horizontal position, making it better suited for feeding on ground vegetation or lower-lying plants. Its head was comparatively small with a more horse-like appearance.
Regarding size, Brachiosaurus was taller, reaching heights of up to 40 feet at the shoulder due to its long forelimbs and upright neck. While Brontosaurus could be longer, around 72 to 85 feet, its overall height was less, around 28 feet. Both were massive, with Brontosaurus weighing 15-30 tons and Brachiosaurus weighing 28-47 tons.
The Brontosaurus’s Unique History
The classification of Brontosaurus has a complex history, leading to confusion about its identity. It was first described and named in 1879 by paleontologist Othniel Charles Marsh. However, in 1903, paleontologist Elmer Riggs argued that Brontosaurus was not distinct enough from Apatosaurus, another sauropod named earlier by Marsh, and reclassified Brontosaurus excelsus as a species of Apatosaurus. This decision led to Brontosaurus being considered invalid for over a century, with many scientific and public references using Apatosaurus instead.
The debate continued, with some paleontologists advocating for its revalidation. A comprehensive study published in 2015, based on a detailed comparison of numerous sauropod features, concluded that Brontosaurus possessed enough unique characteristics to be recognized as its own distinct genus once again.