An arresting image of an apatosaur vertebra

Here’s a cool photo of an apatosaur cervical in anterior view. This is from R. McNeill Alexander’s wonderful book Bones: The Unity of Form and Function, which was published in 1994. The whole book is packed with gorgeous full-color photos like this, and you can still get new copies for cover price (f’rinstance).

I remember stumbling across this image not long after I started working on sauropod vertebrae back in the late 90s, and being completely taken aback by the size of the cervical ribs. Up to that point I’d mostly been grokking the long, graceful cervicals of brachiosaurs, and the ridiculously overbuilt apatosaurine cervical morphology was a real kick in the brainpan. That’s well-trod ground here at SV-POW!, but this is still a beautiful photo. I suspect that the vertebra has been at least somewhat restored — some of the texturing on the condyle and under the diapophyses looks suspiciously like it was applied with tools or maybe just human fingers — but in general this is a pretty faithful representation of what an apatosaur cervical looks like from the front.

One thing that always strikes me about views like this is that you could take the centrum of this vertebra, strip off the neural arch and all the apophyses, and stick it through either one of the cervical ribs loops without scraping the sides. If life, the cervical rib loops held the (comparatively small) vertebral arteries and the (comparatively gigantic) intertransverse diverticula. We know this because that’s how birds are built, and because different apatosaurine specimens show pneumatic traces almost all the way around the inside of the cervical rib loop. The same is true in theropods like Majungasaurus, as Pat O’Connor showed in a lovely figure in his 2006 paper (O’Connor 2006: fig. 16). The volume of air in each of the paired cervical rib loops would have simply dwarfed the volume of air inside or even alongside the centrum. I wanted to visualize that better so I took my trusty old CT cross-section of OMNH 1094 and pasted it on top of this vert, stretching it a bit in GIMP to improve the fit:

Another thing that this photo shows nicely are the pneumatic fossae on the anterior surfaces of the cervical ribs. I’ve seen those features on loads of apatosaur cervical ribs, but I’ve never seen them discussed anywhere. I have thoughts on why those fossae are there, but that story will have to keep for another time.

References

• Alexander, R. McNeill. 1994. Bones: The Unity of Form and Function. Macmillan General Reference, New York, 224 pp.
• O’Connor, P.M. 2006. Postcranial pneumaticity: an evaluation of soft-tissue influences on the postcranial skeleton and the reconstruction of pulmonary anatomy in archosaurs. Journal of Morphology 267: 1199-1226.