Hairy Museum of Natural History

In the comments to last Sunday’s post on the giant South American sauropod Puertasaurus, wolfwalker asked how this new contender for biggest dinosaur ever compares to Amphicoelias fragillimus, a giant North American sauropod named by Edward Drinker Cope in 1878.

Amphicoelias fragillimus (“Doubly hollow and very fragile”) was only known from part of a dorsal vertebra collected near Cañon City, Colorado. Cope reported that the preserved portion of the bone measured 1.5 meters in height, and estimated that the complete vertebra would have been at least 6 feet tall. (The original description is relatively short, and well out of copyright, so I’ve taken the liberty of transcribing it into the HMNH Library. A scan of the description as it appeared in the journal American Naturalist is available elsewhere.)

Unfortunately, today nobody knows where this fossil is. How, you might ask, could anyone lose the better part of a six-foot-tall vertebra? Definitive answers are lacking, but most suspect that it crumbled to pieces in storage or transit (Cope didn’t call it “fragillimus” for nothing). So all we are left with is Cope’s original description and figure (reproduced to the left), making A. fragillimus something of a dinosaurian fish-story—the big one that got away.

Provided that Cope’s description is accurate (a claim not everyone is willing to accept, given the rather colorful state of paleontology at the time), Ampicoelias fragillimus would have been by far the largest diplodocid sauropod ever described. Diplodocids were a family of lean, long and low sauropods, whose members include Apatosaurus (75 feet long), Diplodocus (83 feet long), Barosaurus (93 feet long), and Seismosaurus (110 feet long). Scaling up a Seismosaurus skeleton to make the vertebrae as large as Amphicoelias fragillimus results in an animal about 160 feet long!

How does this compare to the newly-described Puertasaurus reuili? Puertasaurus is estimated to be 115 to 130 feet long, so it couldn’t match the estimated length of Amphicoelias. But Puertasaurus was a titanosaur, a group that had a wider, heavier, and stockier build than their distant diplodocid cousins. So, even though it would have taken more steps to walk the length of Amphicoelias fragillimus, Puertasaurus would still have been a much somewhat more massive animal. This is easy to see when you compare their vertebrae side-by-side: See the revision below:

From left to right:

 

• The diplodocid Seismosaurus hallorum dorsal 3 (from the Jurassic exhibit at the NMMNHS),
• The diplodocid Amphicoelias fragillimus dorsal 9/10? (after Cope 1878),
• The titanosaur Argentinosaurus huinculensis dorsal 4? (after Novas et al 2005),
• The titanosaur Puertasaurus reuili dorsal 2 (ibid). Scale equals 1 meter.

To see the scale of the different animals, I worked up a rough series of silhouettes. Click on the image for a larger version:

From left to right:

• The diplodocid Seismosaurus hallorum (skeleton on display at the NMMNHS–110 ft. long),
• The diplodocid Amphicoelias fragillimus (est. 160 ft. long),
• Homo sapiens (6 ft. tall),
• The titanosaur Argentinosaurus huinculensis (skeleton on display at the Fernbank Museum–123 ft. long),
• The titanosaur Puertasaurus reuili (est. 135 ft. long),
• African Elephant Loxodonta africana (13 ft. tall at the shoulder).

Note that this image is no more than a rough guideline—none of the sauropods are known from more than a 30% complete skeleton, and the proportions of the titanosaurs are particularly sketchy. But I think it is safe to say that the enormous sauropods coming out of South America are giving even the most legendary giants of the western U.S. a run for their money.

Revision 8/18: Something isn’t quite right about the images above.
Something seemed amiss when I saw this image over at NewCritters.com. The Puertasaurus vertebra pictured there couldn’t be as large as I’d made it in the comparison above.

After double-checking the figures in Novas et al.’s paper, I realized that they had illustrated this vertebrae with two different scales. In Figure 2 of the paper, the scale shows it to be consistent with the reported height of 106 centimeters. In Figure 3, where this vertebra is compared to those of other sauropods, the scale shows it to be at least 25% larger. Since the latter figure had an Argentinosaurus vertebra to (what I assumed was) the same scale, I used that figure for the above diagram without double-checking the text. A revised vertebral comparison (showing the discrepancies in the original figures) is shown below:

From left to right:

 

• The diplodocid Seismosaurus hallorum dorsal 3 (from the Jurassic exhibit at the NMMNHS),
• The diplodocid Amphicoelias fragillimus dorsal 9/10? (after Cope 1878),
• The titanosaur Puertasaurus reuili dorsal 2 (after Novas et al 2005, Figure 3),
• The titanosaur Puertasaurus reuili dorsal 2 (after Novas et al 2005, Figure 2). Scale equals 1 meter.

What a difference in size! The smaller version on the right is consistent with the reported measurements and photographs, and I feel fairly confident that this is the correct size. It makes it much smaller, however, and much closer in scale to Seismosaurus than Amphicoelias.

How would this affect the size of the animal? More on that later…

Revision 8/19: Updating the animals

In putting together the silhouette comparison above, I modified an outline of Gabriel Lio’s Puertasaurus restoration for the two titanosaurs. The resulting outlines of Argentinosaurus and Puertasaurus seemed a little beefy to me, but since they were in keeping with the relative sizes of the vertebrae, I figured they were fairly close. With the revised size of the Puertasaurus vertebra, I thought I’d try another method.

A Google image search revealed a couple of good photos of the skeletal reconstruction of Argentinosaurus huinculensis mounted at the Fernbank Museum of Natural History, which comes in at 123 feet long. Using these images, I came up with a revised giant-titanosaur silhouette for Argentinosaurus and Puertasaurus which is considerably more svelte. However, plugging them into the comparison with Seismosaurus and Amphicoelias shows that they were still nothing to sneeze at (click on the image for a larger version):

From left to right:

• The diplodocid Seismosaurus hallorum (skeleton on display at the NMMNHS–110 ft. long),
• The diplodocid Amphicoelias fragillimus (est. 160 ft. long),
• Homo sapiens (6 ft. tall),
• African Elephant Loxodonta africana (13 ft. tall at the shoulder).
• The titanosaur Argentinosaurus huinculensis (skeleton on display at the Fernbank Museum–123 ft. long),
• The titanosaur Puertasaurus reuili (maximum est. 135 ft. long).

—Matt Celeskey.

File under: Cretaceous, Dinosaurs, Jurassic.