Giraffe and human metacarpals compared

May 30, 2020

Here’s one of my most prized possessions: a cannon bone from a giraffe. I got it last fall from Necromance, a cool natural history store in LA. Originally they had a matched pair on display in the front window. Jessie Atterholt got one of them last summer, and I got the other a few months later.

The cannon bones of hoofed mammals consist of fused metacarpals (in the forelimbs) or metatarsals (in the hindlimbs). In this case, the giraffe cannon bone in the top photo is the one from the right forelimb, consisting of the fused 3rd and 4th metacarpals, which correspond to the bones in the human hand leading to the middle and ring fingers. Only my third metacarpal is traced in the top photo. For maximum homology goodness I should have traced MC4, too, but I’m lazy.

I didn’t know that this was a right forelimb cannon bone when I got it. In fact, I only figured that out this afternoon, thanks to the figures and text descriptions in Rios et al. (2016), which I got free through Palaeontologia Electronica (you can too). The weirdly large and perfectly circular holes at the ends of my cannon bone were clearly drilled out by somone, I guess maybe for mounting purposes? At first I thought it might have been to help the marrow cook out of the shaft of the bone during simmering and degreasing, but none of the drilled holes intersect the main marrow cavity, they’re just in the sponge of trabecular bone at the ends of the element.

This post is a sequel to one from last year, “Brachiosaurus and human metacarpals compared“, which featured metacarpal 3 from BYU 4744, the partial skeleton of Brachiosaurus from Potter Creek, Colorado. I know what everyone’s thinking: can we make these two high-browsing giants throw hands?

Yes, yes we can. The giraffe cannon bone is 75.5cm long, and the brachiosaur metacarpal is 57cm long, or 75.5% the length of the giraffe element. I scaled the two bones correctly in the above image. My hands aren’t the same size because they’re at different distances from the camera, illustrating the age-old dictum that scale bars are not to be trusted.

The Potter Creek brachiosaur is one of the largest in the world–here’s me with a cast of its humerus–but ‘my’ giraffe is not. World-record giraffes are about 19 feet tall (5.8m), and doing some quick-and-dirty cross-scaling using the skeleton photo above suggests that the metacarpal cannon bone in a world-record giraffe should be pushing 90cm. So the giraffe my cannon bone is from was probably between 15.5 and 16 feet tall (4.7-4.9m), which is still nothing to sniff at.

I don’t know how this bone came to be at Necromance. I assume from an estate sale or something. I only visited for the first time last year, and at that time they had three real bones from giraffes out in the showroom: the two cannon bones and a cervical vertebra. They might have put out more stuff since–it’s been about six months since I’ve been there–but all of the giraffe bones they had at that point have been snapped up by WesternU anatomists. Jessie and I got the cannon bones, and Thierra Nalley got the cervical vertebra, which is fair since she works on the evolution of necks (mostly in primates–see her Google Scholar page here). I don’t know if there are any photos of Thierra’s cervical online, but Jessie did an Instagram post on her cannon bone, which is nearly as long as her whole damn leg.

There will be more anatomy coming along soon, and probably some noodling about sauropods. Stay tuned!

Reference

Ríos M, Danowitz M, Solounias N. 2016. First comprehensive morphological analysis on the metapodials of Giraffidae. Palaeontologia Electronica 19(3):1–39.

 

 

7 Responses to “Giraffe and human metacarpals compared”

  1. llewelly Says:

    funny. I was just thinking about how strange sauropod feet are (especially the front feet) , and then I came here!

    Such a great comparison. (Of course, for strange metacarpals, my fave is still pterosaurs; metacarpals III and IV, fused in the giraffe, are doing totally different things in a pterosaur! Sauropod metacarpals seem almost normal, despite the odd half-cylinder-like imprint of the forefoot )

  2. Mike Taylor Says:

    This is a really nice example of gene transfer. It’s pretty clear that giraffes’ so-called cannon bones are really azhdarchid cervicals.

  3. llewelly Says:

    Mike is definitely onto something. 55 million years ago, the PETM hyperthermal caused azhdarchid fossils to release weird zoonotic virii, which carried the genes for their weird elongated cervicals, and those virii infected early artiodactyls, leading to the formation of similar bones in artiodactyl limbs, thus contributing to the success and diversification of artiodactyls.

    (so far, the only flying artiodactyls are underwater, but who is to say what the future holds?)

    ha ha ha, only joking.

  4. Mickey Mortimer Says:

    Unrelated, but I’d love to hear SV-POW’s thoughts on…

    ‘Bruce M. Rothschild, Robert A. Depalma, David A. Burnham & Larry Martin (2020)
    Anatomy of a dinosaur–Clarification of vertebrae in vertebrate anatomy.
    Anatomia, Histologia, Embryologia (advance online publication)
    doi: https://doi.org/10.1111/ahe.12573
    https://onlinelibrary.wiley.com/doi/10.1111/ahe.12573

    The flat‐end surfaces of dinosaur vertebral centra led to the presumption that intervertebral discs occupied the space between their vertebrae. A set of fused hadrosaur vertebrae allowed that hypothesis to be tested. The Tyrannosaurus rex responsible for this pathology did not escape unscathed. It left behind a tooth crown that had fractured. Fragments of that tooth were scattered through the intervertebral space, evidencing that there was no solid structure to impede its movement. That eliminates the possibility of an intervertebral disc and instead proves the presence of an articular space, similar to that in modern reptiles, but at variance to what is noted in birds. While avian cervical vertebral centra appear to be separated by diarthrodial joints, the preponderance of their thoracic vertebral centra is not separated by synovial joints.’

  5. LeeB. Says:

    Now you need to get a sivathere cannon bone.
    Also ones from Aepycamelus and Megatylopus or one of the other Giant camels would be good for comparison too.

  6. Maria Says:

    Awesome!!!!

  7. Mark Evans Says:

    Would definitely go with those holes being for a now vanished series of steel mounting rods. Maybe ask Thierra if the cervical had any holes drilled in it? Of course, they might have threaded the vertebrae onto a mount through the neural canals.


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