Brachiosaurus is a genus of extremely large sauropod dinosaur in the family Brachiosauridae known from the late Jurassic period, 154 to 153 million years ago. The name Brachiosaurus means “arm reptile,” in reference to its characteristically long forelimbs. It was first discovered near Fruita, Colorado in 1900, a location that is now part of the Morrison Formation. The specimen consisted of a partial skeleton, lacking a head, but was immediately recognizable for its distinctive anatomical features. In 1901, it was described in a report by paleontologist Elmer S. Riggs, who had excavated the skeleton during the previous year. At the time, it appeared to be the largest-known dinosaur; it was named Brachiosaurus altithorax, meaning “high-chested arm reptile,” in 1903. Remains of this dinosaur are rare, but have been found in Colorado, Oklahoma, Utah, and Wyoming.