Were the biggest sauropods the most pneumatic?
March 19, 2008
In a comment on the previous post, Amanda wrote:
This might be a stupid question (I don’t really believe that there are no such things as stupid quetions) but do you find that sauropod vertebrae are more highly pneumatic in larger sauropods?
This is not only not a dumb question, it is one of most important questions about pneumaticity in sauropods. The answer is complex, but here at SV-POW! we embrace the complexity. So here’s the dope: brachiosaurids had the most highly pneumatic vertebrae of anything that we’ve measured. Nobody’s gotten a mamenchisaur vert into a CT scanner, nor one from Supersaurus. I had a plan all worked out to do the latter, but at the last minute we realized that the darn thing wouldn’t fit through the scanner. Occupational hazard. And not much scanning has been done on titanosaurs, and none at all on the very big ones. So out of the four clades that produced real monsters–mamenchisaurs, diplodocids, brachiosaurs, and titanosaurs–we have hard data on the monsters themselves from only one. Diplodocids and the more derived titanosaurs did have pretty highly pneumatic vertebrae, but not all of them were big. Some were downright dinky. And there were some pretty big sauropods with only moderate pneumaticity, like Jobaria and Camarasaurus. But they weren’t the real monsters; neither of those critters probably topped 1/3 of the mass of the biggest sauropods we have fair remains for, let alone semi-apocryphal gigapods like Amphicoelias and Bruhathkayosaurus. In short, the picture ain’t clean.
Draw a square and divide it into four smaller squares. Label one axis with “Huge: Yes or No” and the other axis with “Highly pneumatic: Yes or No”, where “huge” means something in the 50+ ton range and highly pneumatic means something with more than 60% air in its verts. All of the boxes will be filled but one, which is the “Huge” and “Not highly pneumatic” one. There are small sauropods that were highly pneumatic, but so far no huge sauropods that weren’t, at least based on the evidence in hand.
It doesn’t work out so well statistically, despite what I said in my 2006 SVP abstract. The problem is that the statistical significance comes and goes depending on which taxa are included. That’s a big problem, because there aren’t very many taxa for which we have enough data to make doing the statistics worthwhile. And we have no crunchable numbers on most of the biggest sauropods, including Supersaurus and the biggest mamenchisaurs and titanosaurs, so even the lack of statistical significance in some of the tests might be just an artifact of undersampling the biggest and possibly most pneumatic taxa.
And there is a final caveat, which is that supposedly there is a 2.3 meter femur from the Early Jurassic of Morocco. Not much is known about this. It was mentioned but apparently not figured in one short paper published a while ago in French in a Moroccan journal that is exceedingly hard to get a hold of. If it is really from the Early Jurassic and it really is that big, that’s pretty amazing. A 2.3 meter femur is as big as that of the largest known brachiosaurids. It’s up there in Argentinosaurus country. But in the Early Jurassic it presumably represents something pretty basal, which presumably means something that is not highly pneumatic. You’ll notice that there are a lot of presumablys in there, but if that femur does represent a huge basal sauropod, then we would have to go back to our boxes and put an X in the last one, the “huge” and “not highly pneumatic” box. In which case, forget about any statistical correlation between size and pneumaticity. That giant eopod would be enough to wreck the correlation all by itself.
And I just remembered Turiasaurus, which I should have thought of sooner since I’ve seen the material (nyah nyah). The verts are a little mooshed but not bad. I’ve scanned worse. And the folks in Spain would like to scan it. My guess is that it will come about about like Camarasaurus, in the ~60% zone. It is probably the biggest sauropod with so little pneumaticity, except only the Moroccan monster, assuming my guess is correct (FWIW, when Mike’s tested me in the past my guesses about air space proportion have been pretty darn close).
So what’s the take home message? At least a few sauropods got rilly rilly big without being rilly rilly pneumatic. And at least some rilly rilly pneumatic sauropods were not particularly big. But the biggest sauropods that we know of also seem to be the most pneumatic.
There is another interesting pattern, having to do with neck length and internal complexity of the vertebrae, but I’m going to save that one for another post.
The picture shows the three largest cervical vertebrae of anything, ever, that anyone has found. Until somebody finds some more Amphicoelias fragillimus or Bruhathkayosaurus, this is as long as vertebrae are known to get. Sauroposeidon and Supersaurus are my own photos; Puertasaurus is after Novas et al. (2005:fig. 1). Each of those taxa–heck, each of those vertebrae–is due its own post one of these days, but for now just grok the immensity.