How big was Alamosaurus?
September 2, 2009
Here’s a skeletal reconstruction of Alamosaurus modified from Lehman and Coulson (2002:fig. 11). I cloned the neck and rotated it a few degrees to see where it would put the head.
The skeleton in the figure is scaled to the size of the individuals in the Smithsonian and at UT Austin. The scale bar is 1 meter, which by my calculations gives that individual the following dimensions:
- Total length: 15.8 meters (52 feet)
- Neck length: 5.2 meters (17 feet)
- Shoulder height: 4 meters (13 feet)
- Head height (with neck raised): 8.4 meters (27.5 feet)
Here are a couple of articles on a giant sauropod found in Big Bend in 1999. This critter is generally assumed to be Alamosaurus but it could be something new (I have no evidence either way); the material is currently under study at the Dallas Museum of Nature and Science.
According to the articles, 10 cervical vertebrae were found in a string 23 feet long. From the pictures, those ten vertebrae look like the ten largest, which should account for almost all of the neck except for the first few cervicals behind the head. Let’s assume that this big individual therefore had a neck just a little longer than 23 feet, and we find that it is almost exactly 1.5 times bigger than the one listed above. If its proportions follow those of the Lehman and Coulson recon, its measurements would be:
- Total length: 24 meters (79 feet)
- Neck length: 7.8 meters (25.5 feet)
- Shoulder height: 6 meters (19.5 feet)
- Head height: 12.6 meters (41 feet)
In the second article Homer Montgomery speculates that the complete neck would have been more than 30 feet long. That’s certainly not impossible, since 30-foot-plus necks are known for the largest individuals in several clades (e.g., Mamenchisaurus, Supersaurus, Sauroposeidon, probably Puertasaurus, possibly Futalognkosaurus, but probably not Aegyptosaurus) If so, then you could just about double all of the proportions from the first individual described above, which would give a truly prodigious animal. The 52-foot animal probably had a mass around 15 tons, so the 79-footer would have been about 50 tons (1.5^3 = 3.375), and the hypothetical 100-footer would have been 120 tons, which is up in Amphicoelias/Bruhathkayosaurus territory. For what it’s worth, I think the numbers for the 79-foot animal are more plausible, but who knows. Anytime you’ve got a partial neck that is longer than the complete neck of Diplodocus, you’re dealing with a wacky big animal.
Lehman, T.M. & Coulson, A.B. 2002. A juvenile specimen of the sauropod Alamosaurus sanjuanensis from the Upper Cretaceous of Big Bend National Park, Texas. Journal of Paleontology 76(1): 156-172.