In a comment on the last post, Mike wrote, “perhaps the pneumaticity was intially a size-related feature that merely failed to get unevolved when rebbachisaurs became smaller”.

Caudal pneumaticity in saltasaurines. Cerda et al. (2012: fig. 1).

Or maybe pneumaticity got even more extreme as rebbachisaurids got smaller, which apparently happened with saltasaurines  (see Cerda et al. 2012 and this post).

I think there is probably no scale at which pneumaticity isn’t useful. Like, we see a saltasaurine the size of a big horse and think, “Why does it need to be so pneumatic?”, as if it isn’t still one or two orders of magnitude more massive than an ostrich or an eagle, both of which are hyperpneumatic even though only one of them flies. Even parakeets and hummingbirds have postcranial pneumaticity.

Micro CT of a female Anna’s hummingbird. The black tube in the middle of the neck is the supramedullary airway. Little black dots in the tiny cervical centra are air spaces.

We’re coming around to the idea that the proper way to state the dinosaur size question is, “Why are mammals so lousy at being big on land?” Similarly, the proper way to state the pneumaticity question is probably not “Why is small sauropod X so pneumatic?”, but rather “Why aren’t some of the bigger sauropods even more pneumatic?”

Another thought: we tend to think of saltsaurines as being crazy pneumatic because they pneumatized their limb girdles and caudal chevrons (see Zurriaguz et al. 2017). Those pneumatic foramina are pretty subtle – maybe their apparent absence in other sauropod clades is just because we haven’t looked hard enough. Lots of things have turned out to be pneumatic that weren’t at first glance – see Yates et al. (2012) on basal sauropodomorphs and Wedel and Taylor (2013b) on sauropod tails, for example.

Back of the skull of a bighorn sheep, showing the air spaces inside one of the broken horncores.

Or, even more excitingly, if the absence is genuine, maybe that tells us something about sauropod biomechanics after all. Maybe if you’re an apatosaurine or a giant brachiosaurid, you actually can’t afford to pneumatize your coracoid, for example. One of my blind spots is a naive faith that any element can be pneumatized without penalty, which I believe mostly on the strength of the pneumatic horncores of bison and bighorn sheep. But AFAIK sauropod girdle elements don’t have big marrow cavities for pneumaticity to expand into. Pneumatization of sauropod limb girdles might have come at a real biomechanical cost, and therefore might have only been available to fairly small animals. (And yeah, Sander et al. 2014 found a pneumatic cavity in an Alamosaurus pubis, but it’s not a very big cavity.)

As I flagged in the title, this is noodling, not a finding, certainly not certainty. Just an airhead thinking about air. The comment thread is open, come join me.

References

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Juvenile Tomistoma schlegelii, LACM Herpetology 166483, with me for scale. It wasn’t until I picked up the skull that I realized it was the same specimen I had looked at back when. I was looking at its neck in 2011, and its tail today, for reasons that will be revealed at the dramatically appropriate moment. I was only playing with the skull because it’s cute, an intricate little marvel of natural selection. Photos by Vanessa Graff (2011) and Jessie Atterholt (2018). Many thanks to collections manager Neftali Camacho for his hospitality and assistance both times!

John Yasmer, DO (right) and me getting ready to scan MWC 8239, a caudal vertebra of Diplodocus on loan from Dinosaur Journey, at Hemet Valley Imaging yesterday.

Alignment lasers – it’s always fun watching them flow over the bone as a specimen slides through the tube (for alignment purposes, obviously, not scanning – nobody’s in the room for that).

Lateral scout. I wonder, who will be the first to correctly identify the genus and species of the two stinkin’ mammals trailing the Diplo caudal?

A model we generated at the imaging center. This is just a cell phone photo of a single window on a big monitor. The actual model is much better, but I am in a brief temporal lacuna where I can’t screenshot it.

What am I doing with this thing? All will be revealed soon.

We don’t post on pterosaurs very often, but I’m making an exception for Caelestiventus. Mostly because I had the unusual experience of holding a life-size 3D print of its skull a few days before it was published. Brooks Britt and George Engelmann are both attending Flugsaurier 2018 in Los Angeles, and Brooks gave a talk on the new pterosaur on Friday. It’s from the Upper Triassic Saints & Sinners Quarry in far northeastern Utah, which has also produced theropods, sphenosuchian crocs (like 80 individuals to date, no exaggeration), drepanosaurs (I’ve seen the material and that paper is going to be mind-blowing whenever it arrives), and other assorted hellasaurs. Some of that material is figured in the Britt et al. (2016) paper on the Saints & Sinners Quarry (a free download from the link below). As far as I know, the Caelestiventus paper is the second big volley on the Saints & Sinners material, out of what will probably be a long stream of important papers.

Anyway, since we’ve just been discussing the utility of 3D printing in paleontology (1, 2), I thought you’d like to see this. Brooks did caution us that the 3D model was a work in progress, and he now thinks that Caelestiventus had a more convex dorsal skull margin, with the downward forehead dip in the version that got printed being less prominent or absent. You can see a slightly different version in the skull recon drawn by second author Fabio M. Dalla Vecchia, which he kindly released into the public domain here.

Otherwise the 3D print is pretty good. The big plate below the orbit is weird and from what I gather not present in other dimorphodontids. Because the Saints & Sinners material was buried in sand, which is relatively incompressible compared to mud and clay, it’s all preserved in three dimensions with essentially no crushing. Caelestiventus therefore yields new information about Dimorphodon micronyx, which has been known since 1859 but mostly from pancaked material.

Stay tuned (in general, not here necessarily) for more on the remarkable tetrapods of the Sants & Sinners Quarry – the next few years are going to be very exciting. And since this may be my first and last Flugsaurier post, many thanks to the organizers for making it such an engaging and enjoyable experience, especially Mike Habib, Liz Martin-Silverstone, and Dave Hone.

References

I was back in Utah the week before last, looking for monsters with Brian Engh and Jessie Atterholt. It was a successful hunt – more about that another time.

We made a run to Fruita, Colorado, to visit Dinosaur Journey. I was just there in May, picking up Haplocanthosaurus caudals for CT scanning (and other fun things). We picked up another specimen this time, for a different project – more on that in another post, too.

Not this one, but like this one. An apatosaurine middle caudal vertebra, MWC 5742, in left lateral view.

There’s a nice ceratopsian exhibit up at Dinosaur Journey right now, with cast skulls from many of the new ceratopsians that have been described in the past couple of decades. My near-favorites were Zuniceratops and Diabloceratops, both of which are small enough that they must have been adorable in life (think pony-sized and big-horse-sized, respectively).

My absolute favorite, of course, was this little thing:

I can tell you exactly how Aquilops came to be on display there. Julia McHugh printed a copy of the holotype, because it’s freely available to the world. And she used Brian’s Aquilops head recon in the signage (correctly, with attribution), because it’s also freely available to the world. In fact, I’ve seen Aquilops on display at several museums now for just those reasons. So, folks, if you want your critters to be seen, make them open. Hiring a paleoartist to do some awesome artwork that can be released under a CC-BY license (because you paid them, not because you asked them to give their art away for “exposure”) is a huge help.

We had to geek out a little about unexpectedly finding ‘our’ dinosaur on display:

But of course it is not our dinosaur anymore – that’s the whole point. Aquilops belongs to the world.

For more on our trip, see Jessie’s posts herehere, and here.

Ripple rock. Not from the Morrison, but from the overlying Dakota – Lower Cretaceous.

Now this is from the Morrison. My son, London, spotted this tiny tooth of a Jurassic croc while working in the quarry. That’s my thumb and London’s index finger for scale.

London’s index finger again, pointing at a different Morrison tooth. This one’s from a theropod, still exposed in a sandstone block in one of Stovall’s old quarries from the 1930s.

On a completely different hillside, I spotted this skull, of a modern rodent. Vole, maybe? Not my bailiwick, but if you know who this belongs to, let me know in the comments.

Moonrise – and the end of this post. Catch you in the future.

I’ve known who Peter Doson was since I was nine years old. A copy of The Dinosaurs by William Stout and William Service, with scientific content by Peter, showed up at my local Waldenbooks around the same time as the New Dinosaur Dictionary – much more on The Dinosaurs another time. Then when I started doing research as an undergrad at the University of Oklahoma, Peter’s chapter on sauropod paleobiology in The Dinosauria (Dodson 1990) was one of the first things I read. At the SVP banquet in 2000, I ran into Peter and he shook my hand and said, “Sauroposeidon rocks!” I managed not to swoon – barely.

When I was in Philadelphia this March, Peter invited me to the UPenn vet school for an afternoon. He gave me a tour of the building with its beautiful lecture halls and veterinary dissection lab, and then we spent a couple of hours rummaging around in his office. That was one of the highlights of the trip, because it turns out that Peter and I are both comparative anatomy junkies. He’s been at it for longer, and he has more regular access to dead critters and more space to display them, so his collection puts mine to shame. But he kindly let me play with study whatever I wanted.

 

In fact, he went farther than that: he quizzed me. A lot. I take it that it’s a right of passage for people coming through Peter’s office. It was an enjoyable challenge, and I got photos of a few quiz items so you can play, too. This transversely-sectioned skull was one of the first mystery specimens. I figured it out pretty quickly, for reasons I’ll reveal in a future post. Can you? Post your IDs in the comments.

I don’t remember all of the quiz items. One of them was the dark skull lying upside down behind the ratite skeleton in the photo up top. I had to figure that one out without picking it up, so you have about as much information as I did. We’ll call that one quiz item #2. Embiggenate for all the clues you’ll need.

This wasn’t a quiz item, just something cool: the skull of a large dog with the top of the cranium removed. In the paired cavities at the top, we’re looking down through the frontal sinuses to see the respiratory turbinates in the nasal cavities. The single large space behind is the braincase. At the very front, in the shadowed recess, you can see the cribriform plate of the ethmoid bone, perforated with dozens of holes to let the olfactory nerve endings through from the back of the nasal cavities. We have the same thing on a smaller scale a centimeter or two behind our brows, and oriented horizontally. But what really drew my attention were the linear arrays of paired foramina arcing across the floor of the braincase – holes to let cranial nerves and the internal jugular veins out of the skull, and the internal carotid arteries in. We have the same structures in our heads, of course, but the layout isn’t as neat – our big brains, bent forward at such a sharp angle from the spinal cord, have squished things around a bit.

Here are more skulls, garnished with a human femur and a ratite pelvis and synsacrum. Peter quizzed me on the Archaeoceratops (front) and Auroraceratops (back) skulls on the far right. I IDed them correctly, but only because I spent some quality time with the Alf Museum’s casts when I was reconstructing the skull of Aquilops. On the far left is an alligator skull with injected arteries, which is definitely worth a closer look.

Here’s a dorsal view of the injected alligator skull. The arteries have been injected with red resin, and then all of the soft tissue has been macerated away, leaving just the bone and the internal cast of the arterial tree. Some of the midline bone has been removed here to reveal the courses of the cerebral, ethmoid, and nasal arteries. Also note the artery looping around in the left supratemporal fenestra.

Here’s a look into the right side of the back of the skull, where the lateral wall of the braincase has been Dremeled away to show the course of the internal carotid artery. It’s a very cool demonstration of a bit of anatomy that I had never seen before. For more on cranial blood vessels in crocs, check out the obscenely well-illustrated recent paper by Porter et al. (2016).

To my chagrin, that’s all the good photos I got from Peter’s office – we were too busy passing specimens back and forth and frankly geeking out like a couple of kids. One of my favorite specimens from his office was the mounted foot skeleton of a horse, which Jessie Atterholt had prepared for him when she was his student at UPenn. It’s such a cool preparation that it captured my imagination, and when I got back I warned Jessie that if she didn’t get her own articulated horse foot posted soon, I was going to make something similar for myself and steal her thunder. A couple of months later, her horse foot is up on Instagram – I featured it in this post – and my cow foot is still sitting in pieces, waiting for me to put it together. Here’s a shot of Jessie’s, to hopefully prod me into action:

I didn’t get all of Peter’s quiz questions correct. I knew that the endocast of the pharyngeal pouch in a horse was an endocast, but of what I didn’t know, although I did correctly identify the hyoid apparatus of a horse, mounted separately. And there was a partial cetacean jaw that I misidentified as a shark (in my defense, it was from one of the small, short-faced weirdos). Still, Peter said that I’d done as well as anyone else ever had. That was nice to hear, but I was already happy to have gotten to see and talk about so many cool things with a fellow connoisseur. Thanks, Peter, for a wonderful afternoon, and for permission to post these pictures. I am looking forward to a rematch!

References

  • Dodson, P. 1990. Sauropod paleoecology. In: D.B. Weishampel, P. Dodson, P., & H. Osmolska, (eds), The Dinosauria, 402-407. University of California Press, Berkeley.
  • Porter, W.R., Sedlmayr, J.C. and Witmer, L.M., 2016. Vascular patterns in the heads of crocodilians: blood vessels and sites of thermal exchange. Journal of Anatomy 229(6): 800-824.
  • Stout, W., Service, W., and Preiss, B. 1984. The Dinosaurs: A Fantastic View of a Lost Era. Bantam Dell Publishing Group, 160pp.