The Brachiosaurus, a large, long-necked dinosaur, holds an iconic place in public imagination. Fossil discoveries provide insights into the ancient ecosystems these massive creatures inhabited and their place in the prehistoric world.
The Initial North American Discovery
The primary and most significant discovery of Brachiosaurus altithorax occurred in North America. American paleontologist Elmer S. Riggs, working for the Field Columbian Museum (now the Field Museum of Natural History) in Chicago, unearthed the first known skeleton on July 4, 1900. This discovery took place in the Grand River Valley, near Fruita, Colorado, USA, in an area now known as Riggs Hill.
The fossils were found within the Morrison Formation, a geological formation known for its rich deposits of Late Jurassic dinosaur remains across the western United States. The specimen included a partial skeleton with vertebrae, limb bones, and rib fragments, notably missing a skull. Riggs formally described and named the dinosaur Brachiosaurus altithorax in 1903, a name meaning “arm lizard with a high chest,” referencing its unusually long forelimbs and deep torso. Its unique proportions, with forelimbs longer than hindlimbs, helped define the Brachiosauridae family.
During the Late Jurassic period, approximately 154 to 153 million years ago, the region of the Morrison Formation was characterized by diverse environments. These included semi-arid conditions with seasonal rainfall, floodplains, and river valleys, supporting lush vegetation such as conifers, cycads, and ginkgoes. This warm, humid climate and abundant plant life provided an ideal habitat for large herbivores like Brachiosaurus, which likely browsed on high-growing foliage.
Global Fossil Evidence and Related Species
Beyond North America, significant brachiosaurid discoveries have been made in the Tendaguru Formation in Tanzania, which was formerly German East Africa. These African specimens, excavated between 1909 and 1912, were initially classified by German paleontologist Werner Janensch as Brachiosaurus brancai in 1914. The Tendaguru Formation, also dating to the Late Jurassic period (approximately 150 million years ago), is considered one of Africa’s richest Late Jurassic strata.
Modern taxonomic understanding, however, distinguishes these African specimens from the North American Brachiosaurus altithorax. In 1988, Gregory S. Paul proposed separating the Tanzanian fossils into a distinct genus, Giraffatitan. This reclassification was further supported by a detailed 2009 study by Michael P. Taylor, identifying numerous morphological differences between the North American and African forms. Therefore, the famous skeleton displayed in Berlin’s Natural History Museum, often popularly associated with Brachiosaurus, is actually Giraffatitan brancai.
While Giraffatitan is no longer considered a species of Brachiosaurus, it remains a very close relative within the Brachiosauridae family. The Tendaguru Formation’s environment during the Late Jurassic was similar to the Morrison Formation, featuring coastal and inland vegetated areas. This provided context for the wide geographical distribution of these large, high-browsing dinosaurs.