SV-POW! at 19, and trying to see what’s not there

Today is SV-POW!’s birthday. Not a nasty, dirty, wet birthday, like a 2nd or a 13th, nor yet a grand, nice-round-number birthday like a 10th or a 20th: it is our 19th birthday, and that means we’ve been around a while. I decided to celebrate by posting surprising facts about RNA.

Nah, that was a transparent and rather feeble misdirect. It’s going to be sauropod vertebrae! (Although if you were really hoping for a surprising fact about RNA, hit me up in the comments.)

We’ve talked here about sauropod neck muscles, most recently in the posts linked here, and for obvious reasons. Witmer (1997) evocatively described the form of pneumatic bones as the result of a sort of morphogenetic tug-of-war, in which pneumatic diverticula expand opportunistically and invasively and tend to resorb bone tissue that isn’t actively being maintained, and bone tissue grows and is maintained in response to biomechanical stress. That paper landed almost 30 years ago, right after I’d started studying sauropod vertebrae (in 1996, story told here) and right before I got to start looking at CT scans of sauropod vertebrae (in 1998, story told here), it was one of the first things I read when I started working on pneumaticity, and it’s been part of my intellectual bedrock ever since.

It struck me with the force of inevitability that the shapes of sauropod vertebrae were driven by a small constellation of factors: supporting great weight and long necks and tails — mostly compressive forces; resisting or accommodating the forces exerted by muscles, tendons, and ligaments — mostly tensile, at least up close;* doing those thing with the same basic developmental Lego kit as virtually all other vertebrates (as touched on here, and, er, way back here) — but with the spicy addition of pneumatic diverticula, with their rabid tendency to cart away everything not nailed down. Or more succinctly:

vertebra shape = development + size + muscles – pneumatization

*Two or more tension members can load a bony element in compression by pulling on opposite sides to snug it down tight to the next bone in line, but where the muscle or tendon fibers actually attach, the force exerted on the bone tissue will be primarily tensile.

It is almost a haunting thought — if diverticula have removed all the bone that isn’t being loaded,* then the forms of sauropod vertebrae should be their biomechanical loading regimes incarnate, and it feels like we should be able to easily visualize where all the muscles, tendons, and ligaments attached. Alas, that “easily” is more of a “hardly”, because vertebrae are kind of a biomechanical nightmare of complex forces and lots and lots of muscles, big and small, and we’re still uncertain about some basic stuff like which vertebrae had synovial intervertebral joints and which had fibrocartilaginous discs (birds have both in the same vertebral column), and there are probably limits to how far we can get just tracing bird muscles (or croc muscles, or what have you) onto sauropod vertebral columns, not least because birds are spectacularly diverse, sauropods were pretty darned disparate themselves, as well as freakin’ huge, and those two lineages parted ways well over 200 million years ago.

*To a first approximation — there are exceptions to the hypothesis of “optimization by pneumatization” in its purest form (f’rinstance).

How complex are we talkin’? Well, here’s a very simple, diagrammatic map to the neck muscles of the chicken, from Zweers et al. (1987: fig. 7). Not multiple chickens, like different individuals or breeds, just…a chicken. Any chicken. Every chicken. Even drawing each slip of muscle as a line, and packing things together almost to the limit of readability, it still took four different diagrams to show the muscles on one side of one neck from one angle. In a chicken. A chicken!!

So when in future posts in this series I talk blithely about the longus colli dorsalis muscles of sauropods inserting on their epipophyses, or anything along those lines, I want you to do three things: (1) remember that simple, line-based diagram from Zweers, that isn’t even trying to represent the muscles realistically, but only to map their connections; (2) think about trying to translate that to animals with necks as long as tour buses; and (3) take everything that I or anyone else ever says on this topic with an evaporated ocean of salt.

But still. We oughta be able to figure some things out, right? Stay tuned.

Thanks for reading, whether you’ve been here from the start or you’re one of the readers we picked up along the way (at this point, possibly because you were born along the way). And thanks to Mike and Darren, for a conversation 19 years ago that hatched a joke that became a blog that wholly unexpectedly evolved into one of the biggest and most rewarding things I’ve done, and for all the years of inspiration, support, and friendship along the way. Next round’s on me.

References

• Schwarz, D., Frey, E., and Meyer, C.A. 2007. Pneumaticity and soft−tissue reconstructions in the neck of diplodocid anddicraeosaurid sauropods. Acta Palaeontologica Polonica 52(1):167–188.
• Wedel, Mathew J., and Michael P. Taylor. 2023. The biomechanical significance of bifurcated cervical ribs in apatosaurine sauropods. VAMP (Vertebrate Anatomy Morphology Palaeontology) 11:91-100. doi: 10.18435/vamp29394
• Witmer, L.M. 1997. The evolution of the antorbital cavity of archosaurs: a study in soft-tissue reconstruction in the fossil record with an analysis of the function of pneumaticity. Journal of Vertebrate Paleontology 17(Supplement 1): 1-76.
• Zweers GA, Vanden Berge JC, Koppendraier R. 1987. Avian cranio-cervical systems. Part I: Anatomy of the cervical column in the chicken (Gallus gallus L.) Acta Morphologica Neerlando-Scandinavica 25:131–155.

Source: https://svpow.com/2026/10/01/sv-pow-at-19-and-trying-to-see-whats-not-there/