Amphicoelias fragillimus
"very fragile double cavity"

In 1878, E.D. Cope discovered a gigantic dinosaur vertebra in Colorado. In a very bad state of preservation, the vertebrae was catalogued, described, drawn, and lost. All that remains is a drawing in Cope's description, which claims the vertebra was eight feet high. Cope, recognizing the bone as belonging to a gigantic sauropod of the previously known genus Amphicoelias, assigned the vertebra to the new species Amphicoelias fragillimus. The specific name (meaning "very fragile") is an appropriate designation, since the bone probably crumbled to dust. A. fragillimus was one of the largest dinosaurs ever found, with a length of around 200ft and a mass exceeding that of the largest known titanosaurs.

Here I've reconstructed A. fragillimus as a basal diplodocomororph (like A.altus, Rebacchisaurus, etc.). Flocking around the huge neck of the animal, as well as roosting in its back (a behavior based on that of African oxpecker birds), is the undescribed pterodactyl genus Wyomingopteryx. Wyomingopteryx has never been mentioned in scientific literature save for a single painting by Bob Bakker, so it's validity is almost as questionable as A. fragillimus itself. The new 2005 reconstruction shows an updated posture for this dinosaur, based on the research of Kent Stevens. Diplodocid sauropods like Amphicoelias used their long necks to sweep the ground as they foraged for ferns and other low-growing plants. Contrary to popular depictions, these dinosaurs would not have been able to raise their heads above shoulder level.

Click here to view the original description of A. fragillimus, with drawings of the known skeletal material: Page 1, Page 2