Barosaurus means heavy lizard, and was first described by Othniel Charles Marsh in 1890. It is a plant eating sauropod - a "long-neck", capable of growing 75-90 feet (23-27 meters). The specimen the cast was based on, was collected by Earl Douglass and his crews between 1912 and 1914, from Utah (AMNH-6341 Dinosaur National Monument, Utah). It seemed to be another Diplodocus sauropod by the crew and not the scarce Barosaurus it was. Several museums were missing parts for their mounts so a tail section went to Pittsburgh's Carnegie Museum, a section of neck to the Smithsonian Institution, Washington, D.C., with the rest going to the University of Utah.

It took Barnum Brown, one of the premier AMNH dinohunters, to bring the specimen to New York and not in his usual way of digging it up from the ground. In 1929, Brown realized the seperate specimens were Barosaurus and not Diplodocus. Wheeling and dealing, with cash, a three-toed horse, and Albertosaurus, he managed to unite the specimens.

The sediments the fossils were found in date to the late Jurassic, about 140 million years ago. Other diplodocids Diplodocus, Apatosaurus, and the Chinese Mamenchisaurus existed around this time as well as the other large sauropods, Brachiosaurus, and Camarasaurus. It was not a good time to be a tree!