Arm lizard

December 16, 2019

Reconstructed right forelimb of Brachiosaurus at Dinosaur Journey in Fruita, Colorado, with me for scale, photo by Yara Haridy. The humerus is a cast of the element from the holotype skeleton, FMNH P25107, the coracoid looks like a sculpt to match the coracoid from the holotype (which is a left), and the other elements are either cast or sculpted from Giraffatitan. But it’s all approximately correct. The actual humerus is 204cm long, but the distal end is eroded and it was probably 10-12cm longer in life. I don’t know how big this cast is, but I know that casts are inherently untrustworthy so I suspect it’s a few cm shorter than it oughta be. For reference, I’m 188cm, but I’m standing a bit forward of the mount so I’m an imperfect scale bar (like all scale bars!). For another view of the same mount from five years ago, see this post.

So I guess the moral is that even thought this reconstructed forelimb looks impressive, the humerus was several inches longer, even before we account for any shrinkage in the molding and casting process, and the gaps between the bones for joint cartilage should probably be much wider, so the actual shoulder height of this individual might have been something like a foot taller than this mount. A mount, by the way, that is about as good as it could practically be, and which I love — I’m including all the caveats and such partly because I’m an arch-pedant, and partly because it’s genuinely useful to know all the ways in which a museum mount might be subtly warping the truth, especially if you’re interested in the biggest of the big.

All of which is a long walk to the conclusion that brachiosaurs are pretty awesome. More on that real soon now. Stay tuned.

7 Responses to “Arm lizard”

  1. Mike Taylor Says:

    My name is Mike Taylor, and I endorse this message.

  2. Matt Wedel Says:

    After a few posts on groady little critters like swine and (shudder) Cam, I needed a palate cleanser.

  3. Professional Paleoartist Reginald Shrinkwrappington The 4th Says:

    Would it be possible to get that measurement in Clydesdales?

  4. Amy H Says:

    I hadn’t ever thought about the joint cartilage being thicker. Would the distance shown have made it an arthritic brachiosaur?

  5. Mike Taylor Says:

    Yep. Think about the proportional thickness of the cartilage between femur and tibia when you eat a roast chicken. The unfinished, rugose articular surfaces of sauropod limb bones indicate a similar proportional thickness.

  6. Matt Wedel Says:

    Dr. Shrinkwrappington, always a pleasure to have you visit.

    Would it be possible to get that measurement in Clydesdales?

    We can try! The Clydesdales I worked with most recently were about 6′ at the withers and weighed 1800 lbs. The Brachiosaurus holotype was probably about 20′ at the withers. That’s 3.33x the withers height of the Clydesdales, or 37x the mass (assuming, illogically, that Brachiosaurus was just a scaled-up Clydesdale). Strangely, though, 37 times 1800 lbs is 33 short tons or 30 metric tons, which is a pretty reasonable mass estimate for the Brachiosaurus altithorax holotype. So if you want to think of a big brachiosaur as 30-40 Clydesdales worth of awesome, you’ll at least be in the right ballpark.

    Pairs of draft horses have pulled loads up to 45 tons, and a single draft horse has pulled a 29-ton load (sources and photos here). So if you could get a big brachiosaur to stand on a sled, two Clydesdales could probably pull it. If it was only a fair-to-middlin’ brachiosaur, like MB.R.2181 (formerly HMN SI), a single Clydesdale might be enough to get the job done. Crazy.

    How much weight a brachiosaur could pull (or more likely push, given the pathetic state of harnesses and other tack in the Mesozoic) is a truly inspiring thought.

  7. Matt Wedel Says:

    Relevant to the strange path this discussion has taken: in addition to ruling the sea and earthquakes, Poseidon was also the god of horses. So Sauroposeidon (although probably not a brachiosaur, still brachiosaur-adjacent as a basal titanosaur) could be read as “lizard god of horses” — a thought that was definitely in my mind while I was coining the name.


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