In the North American Barosaurus lentus (Marsh, 1890), the skull, front of the neck, forearm and manus, and distal half of the tail remain unknown. The genus is very closely related to Diplodocus, and the limb bones are so similar as to be indistinguishable. Barosaurus differs from Diplodocus is its enormously elongated cervical vertebrae, which are relatively 33 percent longer than those of the latter.