Brachiosaurus - Discovery and History

Discovery and History

The genus Brachiosaurus, and type species B. altithorax, are based on a partial postcranial skeleton from Fruita, in the valley of the Colorado River of western Colorado. This specimen was collected from rocks of the Brushy Basin Member of the Morrison Formation in 1900 by Elmer S. Riggs and his crew from the Field Columbian Museum (now the Field Museum of Natural History) of Chicago. It is currently cataloged as FMNH P 25107. Riggs and company were working in the area as a result of favorable correspondence between Riggs and S. M. Bradbury, a dentist in nearby Grand Junction. In 1899 Riggs had sent inquiries to rural locations in the western United States concerning fossil finds, and Bradbury, an amateur collector himself, reported that dinosaur bones had been collected in the area since 1885. It was Riggs' field assistant H. W. Menke who found FMNH P 25107, on July 4, 1900. The locality, Riggs Quarry 13, was found on a small hill later known as Riggs Hill; it is marked by a plaque. Additional Brachiosaurus fossils are reported on Riggs Hill, but other fossil finds on the hill have been vandalized. Riggs published a short report in 1901, noting the unusual length of the humerus compared to the femur and the extreme overall size and the resulting giraffe-like proportions, as well as the lesser development of the tail, but did not publish a name for the new dinosaur. The titles of Riggs (1901) and (1903) suggested that the specimen was the largest known dinosaur. Riggs followed his 1903 publication that named Brachiosaurus altithorax with a more detailed description in a monograph in 1904.

The Fruita skeleton was not the first discovery of Brachiosaurus bones, although it was the first to be recognized as belonging to a new and distinct animal. In 1883, a sauropod skull was found near Garden Park, Colorado, at Felch Quarry 1, and was sent to Othniel Charles Marsh (of "Bone Wars" fame). Marsh incorporated the skull into his skeletal restoration of "Brontosaurus" (now Apatosaurus). It eventually became part of the collections of the National Museum of Natural History, as USNM 5730. In the 1970s, when Jack McIntosh and David Berman were working on the issue of the true skull of Apatosaurus, they reevaluated the Garden Park skull as more similar to Camarasaurus. It was described and recognized as a Brachiosaurus skull in 1998 by Kenneth Carpenter and Virginia Tidwell, intermediate in form between Camarasaurus and Giraffatitan brancai (then still considered to be B. brancai). Because there are no overlapping parts between this skull and FMNH P 25107, it cannot be confidently assigned to a species, so it is classified as Brachiosaurus sp.

Additional discoveries of Brachiosaurus material in North America have been uncommon and consist of a handful of bones. Material has been described from Colorado, Oklahoma, Utah, and Wyoming, and undescribed material has been mentioned from several other sites. One of these specimens, a shoulder blade from Dry Mesa Quarry, Colorado, is one of the specimens at the center of the Supersaurus/Ultrasauros issue of the 1980s and 1990s. In 1985, James A. Jensen described disarticulated sauropod remains from the quarry as belonging to several taxa, including the new genera Supersaurus and Ultrasaurus, the latter renamed Ultrasauros shortly thereafter because another sauropod already had the name. Later study showed that the "ultrasaur" material mostly belonged to Supersaurus, although the shoulder blade did not. Because the holotype of Ultrasauros, a back vertebra, was one of the specimens that was actually from Supersaurus, the name Ultrasauros is a synonym of Supersaurus. The shoulder blade is now assigned to Brachiosaurus, but the species is uncertain. In addition, the Dry Mesa "ultrasaur" was not as large as had been thought; the dimensions of the shoulder's coracoid bone indicate that the animal was smaller than Riggs' original specimen of Brachiosaurus.