"The centra [of the dorsal vertebrae] differ from those of Camarasaurus in the form of their articular extremities...They are unequally amphicoelous, the posterior extremity being more concave." Marsh (1881) later disputed the diagnostic value of the feature and the validity of Cope's proposed family Amphicoeliidae, because "all the known Sauropoda...have similar vertebrae [near the sacrum], with opisthocoelian centra in the cervical and anterior dorsal region." One extremely large partial dorsal vertebra described by Cope in 1878 under the name A. fragillimus  would have been over eight feet tall if complete, and must have belonged to an animal close to 170 feet in length. Unfortunately, this astonishing specimen is now lost. Amphicoelias remains a poorly known, but possibly diagnosable genus, with newly discovered material yet to be described. McIntosh sees "no reason not to consider [A. fragillimus] a very large individual of A. altus". (1998, Modern Geology 23:481-506).