Illustration of Edward Drinker Cope with Amphicoelias fragillimus vertebra. Complete, the bone would probably have been over 8 feet tall. Illustration from Carpenter (1995).

Amphicoelias is a genus of giant sauropod that possibly includes the largest land animal ever found. While it was enormous, Amphicoelias was also very slender, its build slighter than that of the bulkier and much more common Camarasaurus. Amphicoelias was an herbivore, though it probably didn’t eat as coarse of material as Camarasaurus did.

Garden Park is the type locality for all three of the Amphicoelias species Cope named: Amphicoelias altus, A. latus, and A. fragillimus. The type specimen of A. altus was known as “A. Ripley’s Fossil” and was probably found by Aaron Ripley, the husband of Oramel and Ira Lucas’s sister Lucy. According to Cope’s notes, one A. latus femur ended up at Oberlin College. Oramel Lucas had probably brought it back with him to school in 1878. The fossil appears to have since been lost, however, as recent attempts to locate it at Oberlin have failed (McIntosh, 1998). Osborn and Mook (1921), along with every subsequent researcher of Amphicoelias, considered A. altus and A. latus to be the same species. A living Amphicoelias altus would have been around 98 feet long, but was so slender it would have "only" weighed about 30 tons or roughly 27 metric tons (Carpenter, 1995). Amphicoelias fragillimus, however, was much larger.

Size comparison between Amphicoelias altus (green), A. fragillimus (orange), and an average human (blue). Image by Matt Martyniuk, retrieved 2011. Click for larger image.

Amphicoelias fragillimus is only known from one enormous fragmented vertebra (about 4.9 feet, or 1.5 meters tall) and the end of a femur (Cope, 1878), both of which have been lost. If complete, the vertebra would probably have been well over 8 feet tall (2.7 meters). Carpenter (2006) estimated the length of A. fragillimus at 190 feet long (about 58 meters), which is within the range suggested by Paul (1994) of 40-60 meters or 131-196 feet . Even conservative estimates of 130 feet (40 meters) would still make A. fragilimus by far the longest animal ever found.  While weight is even more difficult to estimate, Carpenter (2006) calculated that A. fragillimus could have weighed up to 130 tons (118 metric tons). This would make Amphicoelias fragillimus heavier than any other known dinosaur, with the possible exception of Bruhathkayosaurus, another sauropod whose fragmentary remains have not yet been properly described.

Size comparison between the five longest known dinosaurs, with an average human in the lower left for scale. Amphicoelias fragillimus (red) is shown here estimated at a length of 190 feet (58 meters), clearly dwarfing every other sauropod. Image by Matt Martyniuk, retrieved 2011. Click for larger image.

The gigantic size and disappearance of the A. fragillimus bones have caused many to believe the entire thing was a hoax. Many arguments point to the find being real, however. For example, Marsh never seemed to question the gigantic Amphicoelias bone, and Marsh was a ferocious and meticulous critic of Cope’s (Carpenter, 2006). Osborn and Mook (1921) did not seem to question that the giant vertebra existed at some point, even if it is lost now.

Drawing by E. D. Cope of a herd of semi-aquatic Amphicoelias. Most paleontologists today think of sauropods as land animals and would consider this reconstructed scene unlikely. Click on the picture for a larger image.

Scientists in Cope’s time were amazed at the size of sauropods, even without counting the gigantic A. fragillimus. Many people, including Cope, thought that they were far too large to support their weight on land and therefore must have spent the majority of their time in the water. Today most paleontologists believe sauropods to be primarily land animals.

Osborn and Mook (1921) and McIntosh (1998) considered A. fragillimus to be simply a large A. altus, but Carpenter (2006) argued that from Cope’s descriptions it was different enough to be its own species. Confirmation of whether they are the same species or not is almost impossible without the actual bones of A. fragillimus to examine.

Noting many similarities between them, Foster (2007) and others have suggested that Amphicoelias and Diplodocus belong to the same genus. If further research supports this, the name Diplodocus would have to be abandoned for Amphicoelias, as that name was published first. Osborn and Mook (1921) also noted the similarities between Amphiceolias and Diplodocus, though they kept them as separate genera. 

References

Carpenter, K., 1995, The Dinosaurs of Marsh and Cope: Cañon City, Colorado, Garden Park Paleontology Society, p. 22.

Carpenter, K., 2006, Biggest of the big: a critical re-evaluation of the mega-sauropod Amphicoelias fragillimus, in Foster, J. R., and Lucas, S. G., eds., Paleontology and Geology of the Upper Jurassic Morrison Formation: New Mexico Museum of Natural History and Science Bulletin, no. 36, p. 131-138.

Cope, E. D.,1878, A new species of Amphicoelias: American Naturalist, v. 12, no. 8, p. 563-564.

Foster, J., 2007, Jurassic West: The Dinosaurs of the Morrison Formation and Their World: Bloomington, Indiana University Press, 389 p.

McIntosh, J. S., 1998, New information about the Cope collection of sauropods from Garden Park, Colorado: Modern Geology, v. 23, p. 481-506.

Osborn, H. F., and Mook, C. C., 1921, Camarasaurus, Amphicoelias, and other sauropods of Cope: Memoirs of the American Museum of Natural History, New Series, v. 3, Part 3, p. 247-387.

Paul, G. S., 1994, Big sauropods - really, really big sauropods: The Dinosaur Report, The Dinosaur Society, Fall, p. 12-13.