Mike’s and Matt’s excellent adventure in Pittsburgh continues! Today was Day 4, and just as yesterday offered us a unique opportunity to see the mounted Dipodocus and Apatosaurus skeletons up close on a lift, so today we got to look the two mounts from directly above!

Thanks to our host Amy Henrici and to Calder Dudgeon, we were able to go up to the maintenance balconies above the dinosaur hall, and from there we were able to see this:

It was a little bit scary up there: here’s Matt’s vertical panorama photo of me. Just below the balcony I’m standing on you can see another, which is actually far below up but further back. Below that is the main balcony that overlooks the hall. And below that, the hall itself, showing Diplodocus from above:

We think this is a first: we don’t know of any published photos of mounted sauropods from above — but now, there are some. Let’s take a closer look at the torsos:

Diplodocus carnegii holotype CM 84, torso, in dorsal view, anterior to right.

Apatosaurus louisae holotype CM 3018, torso, in dorsal view, anterior to left.

You can immediately see from here that Apatosaurus is a much broader animal than Diplodocus. That much, we could have guessed. What’s more interesting is that Apatosaurus seems to be slightly broader at the shoulders than at the hips, whereas the opposite is the case in Diplodocus.

This observation left us wondering what’s known about the relative widths of the forelimb and hindlimb articulations in extant animals. What, from the modern bestiary, has hips broader than its shoulders, and what has shoulders wider than its hips? We have no idea. Does anyone know if this has been studied, or better yet summarised?

We jumped the gun a bit in asking How fat was Camarasaurus? a couple of years ago, or indeed How fat was Brontosaurus? last year. As always, we should have started with extant taxa, to get a sense of how to relate bones to live animals — as we did with neck posture.

So here we go. I give you a herd of Indian elephants, Elephas maximus (from here):

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You will notice, from this conveniently-close-to-anterior view, that their torsos bulge out sideways, much further than the limbs.

Now let’s take a look at the skeleton of the same animal in the Oxford University Museum of Natural History (downloaded from here but for some reason the photo has now gone away):

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The rib-cage is tiny. It doesn’t even extend as far laterally as the position of the limb bones.

(And lest you think this is an oddity, do go and look at any mounted elephant skeleton of your choice, Indian or African. They’re all like this.)

What’s going on here?

Is Oxford’s elephant skeleton mounted incorrectly? More to the point, are all museums mounting their elephants incorrectly? Do elephants’ ribs project much more laterally in life?

Do elephants have a lot of body mass superficial to the rib-cage? If so, what is that mass? It’s hard to imagine they need a huge amount of muscle mass there, and it can’t be guts. Photos like this one, from the RVC’s televised elephant dissection on Inside Nature’s Giants, suggest the ribs are very close to the body surface:

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I’m really not sure how to account for the discrepancy.

Were sauropods similarly much fatter than their mounted skeletons suggest? Either because we’re mounting their skeletons wrongly with the ribs too vertical, or because they had a lot of superficial body mass?

Consider this mounted Camarasaurus skeleton in the Dinosaur Hall at the Arizona Museum of Natural History (photo by N. Neenan Photography, CC-BY-SA):

Camarasaurus_skeleton

Compare the breadth of its ribcage with that of the elephant above, and then think about how much body bulk should be added.

This should encourage palaeoartists involved in the All Yesterdays movement to dramatically bulk up at least some of their sauropod restorations.

It should also make us think twice about our mass estimates.