Brachiosaurus, a large, long-necked dinosaur from the Jurassic period, is widely recognized for its towering stature. This herbivore featured a distinct posture, characterized by forelimbs that were notably longer than its hind limbs, giving its back a downward slope from its shoulders.
Initial Discoveries in North America
The first significant discovery of Brachiosaurus fossils occurred in North America. In 1900, American paleontologist Elmer S. Riggs uncovered a partial skeleton near Fruita, Colorado, in the Grand River Valley. This find was located within the Morrison Formation, a geological formation spanning several western U.S. states and known for its rich dinosaur fossil record. Riggs formally described the dinosaur in 1903, naming it Brachiosaurus altithorax, which translates to “arm lizard with a deep chest,” referencing its long forelimbs and deep torso.
The initial specimen, though partial, provided sufficient details to establish Brachiosaurus as a distinct genus. It included vertebrae, ribs, and limb bones, allowing for an understanding of its unique proportions. While other fragmentary Brachiosaurus fossils have since been found in locations like Utah, Wyoming, and Oklahoma, the Colorado discovery remains the foundational type specimen for the genus.
The Tendaguru Expeditions in Africa
Major discoveries of brachiosaurid fossils also took place in German East Africa, now modern-day Tanzania. Between 1909 and 1912, German paleontological expeditions, notably led by Werner Janensch, extensively excavated the Tendaguru Beds. These expeditions yielded an exceptionally large volume of sauropod fossils, uncovering over 230 metric tons of bones, including many initially attributed to Brachiosaurus. These finds included multiple partial skeletons, providing a more complete picture of the African brachiosaurid than the North American material. A prominent result of these expeditions is the mounted skeleton displayed at Berlin’s Natural History Museum, which stands as the tallest mounted dinosaur skeleton in the world.
Understanding Brachiosaurus Classification and Global Distribution
While historically, much of the African brachiosaurid material was referred to as Brachiosaurus, scientific re-evaluation led to a reclassification. Most of the fossils from the Tendaguru Formation, including the famous Berlin specimen, were later assigned to a separate genus, Giraffatitan, in 1988. This distinction was based on significant anatomical differences found between the African specimens and the North American Brachiosaurus altithorax. Therefore, “true” Brachiosaurus altithorax fossils are primarily known from North America, specifically the Morrison Formation.
The presence of related but distinct sauropods like Brachiosaurus and Giraffatitan on different continents can be understood through the lens of ancient Earth’s geography. During the Late Jurassic period, when these dinosaurs lived, the supercontinent Pangaea was beginning to fragment. This continental configuration allowed for the widespread distribution of sauropod lineages, which then diversified as landmasses separated over millions of years.