Another mystery: embossed laminae and “unfossae”
December 7, 2009
Broadly speaking, pneumatic sauropod vertebrae come in two flavors. In more primitive, camerate vertebrae, modeled here by Haplocanthosaurus, the centrum is a round-ended I-beam and the neural arch is composed of intersecting flat plates of bone called laminae (lam above; fos = fossa, nc = neural canal, ncs = neurocentral suture; Ye Olde Tyme vert pic from Hatcher 1903).
In more derived, camellate vertebrae, the centrum and neural arch are both honeycombed with many small air spaces. This inflated-looking morphology is very similar to that seen in birds, like the turkey we recently discussed. The fossae and foramina on the outside tend to be smaller and more numerous than in camerate vertebrae, as shown here in a titanosauriform axis from India (Figure 3 from Wilson and Mohabey 2006). The green arrows show that the fossae visible on the external surface are excavations or depressions into the honeycombed internal structure of the bone.
External fossae on bones can house many different soft tissues, including muscles, pads of fat or cartilage, and pneumatic diverticula (O’Connor 2006). Pneumatic fossae are often strongly lipped and internally subdivided and may contain pneumatic foramina, which makes them easier to diagnose (but they may also be simple, smooth, and “blind”, which makes them harder to diagnose as pneumatic). But in all of these cases we are usually talking about the same thing: a visible excavation into a corpus of bony tissue, which may have marrow spaces inside if it is apneumatic, or air spaces inside if it is pneumatic (the corpus of bone, not the dent). That’s probably how most of us think about fossae, and it would hardly need to be explained…except that sometimes, something much weirder happens.
Consider this cervical of Brachiosaurus (this is BYU 12866, from Dry Mesa, Colorado). Brachiosaurus and Giraffatitan have an in-between form of vertebral architecture that my colleagues and I have called semicamellate (Wedel et al. 2000); the centrum does have large simple chambers (camerae), but smaller, thin-walled camellae are also variably present, especially along the midline of the vertebra and in the ends of the centrum. As in Haplocanthosaurus, the neural arch is composed of intersecting plates of bone; unlike Haplocanthosaurus, these laminae are not flat or smooth but are instead highly sculpted with lots of small fossae. Janensch (1950) called these “Aussenkaverne”, or accessory outside cavities, because and they are smaller and more variable than the large fossae and foramina that invade the centrum.
And that’s the weird thing. As the red arrows in the above image show, the “Aussenkaverne” are not excavations or depressions into anything, except the space on the other side of the lamina (which in life would have been occupied by another diverticulum). The neural arches of Brachiosaurus and Giraffatitan are not excavated by fossae, they’re embossed, like corporate business cards and fancy napkins.
What’s up with that!? We tend to think of pneumaticity as reducing the mass of the affected elements, but the shortest distance between two vertebral landmarks is a smooth lamina. These embossed laminae actually require slightly more bony material than smooth ones would.
As you can see above, the outer edges of the laminae are thick but the bone everywhere else is very thin. Maybe, like the median septa in pneumatic sauropod vertebrae, the thin bone everywhere except the edges of the laminae was just not loaded very much or very often, and was therefore free to get pushed around by the diverticula on either side, in the sense of being continually and quasi-randomly remodeled into shapes that don’t strike us as being very mechanically efficient. But also like the median septa, the thin parts of the laminae are only rarely perforated (but it does happen), for possible (read: arm-wavy) reasons discussed in the recent FEA post. And maybe the amount of extra bone involved in making embossed laminae versus smooth ones was negligible even by the very light standards of sauropod vertebrae.
Another question: since these thin sheets of bone were sandwiched in between two sets of diverticula, why are the “unfossae” always embossed into them, in the medial or inferior direction? Why don’t any of them pop out laterally or dorsally, looking like domes or bubbles instead of holes, like Mount Fist-of-God from Larry Niven’s Ringworld? Did the developmental program get accustomed to making fossae that went down and into a corpus of bone, and just kept on with business as usual even when there was no corpus of bone to excavate into? I’m only half joking.
I don’t have good answers for any of these questions. I scanned this vert a decade ago and I only noticed how weird the “unfossae” were a few months ago. I’m putting all this here because “Hey, look at this weird thing that I can only wave my arms about” is not a great basis for a peer-reviewed paper, and because I’d like your thoughts on what might be going on.
In Other News
The Discovery Channel’s Clash of the Dinosaurs premiered last night. I would have given you a heads up, except that I didn’t get one myself. I only discovered it was on because of a Facebook posting (thanks, folks!).
COTD is intended to be the replacement, a decade on, for Walking With Dinosaurs. I’m happy to report that one of the featured critters is Sauroposeidon. I grabbed a couple of frames from the clips posted here.
I haven’t seen the series yet, because I don’t have cable. But I’m hoping to catch it at a friend’s place next Sunday night, Dec. 13, when the entire series will be shown again. With any luck, I’ll have more news next week.
Finally, I got to do an interview at Paw-Talk, a forum for all things animal. I’m very happy with how it turned out, so thanks to Ava for making it happen. While you’re over there, have a look around, there’s plenty of good stuff. Brian Switek, whom you hopefully know from this and this, is a contributor; check out his latest here.
References
- Hatcher, J.B. 1903. Osteology of Haplocanthosaurus, with a description of a new species, and remarks on the probable habits of the Sauropoda, and the age and origin of Atlantosaurus beds. Memoirs of the Carnegie Museum 2:1–72.
- Janensch, W. 1950. Die Wirbelsaule von Brachiosaurus brancai. Palaeontographica (Suppl. 7) 3:27-93.
- 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.
- Wedel, Mathew J., Richard L. Cifelli and R. Kent Sanders. 2000. Osteology, paleobiology, and relationships of the sauropod dinosaur Sauroposeidon. Acta Palaeontologica Polonica 45(4): 343-388.
- Wilson, J. A. and Mohabey, D. M. 2006. A titanosauriform axis from the Lameta Formation (Upper Cretaceous: Maastrichtian) of central India. Journal of Vertebrate Paleontology 26:471–479.
CT-Scanning the Archbishop
November 18, 2009
Last week, for the first time ever, I spent the entire working week on palaeo. I took a week away from my job, and spent it staying in London, working on the Archbishop at the Natural History Museum. (For those of you who have not been paying attention, the Archbishop is the informal name of the specimen NHM R5937, a brachiosaurid sauropod from the same Tendaguru area that produced Giraffatitan brancai, and which has been generally assumed to represent that species.)
Brachiosauridae incertae sedis NHM R5937, "The Archbishop", Cervical U in right lateral view. Photo copyright the NHM since it's their specimen.
My main goal was to take final publication-quality photographs that I can use in the description (which I have committed to try really, really hard to get submitted by the end of 2009). There’s quite a bit of material (more than for Xenoposeidon, anyway!) — six cervicals in various states of preservation/preparation, cervical ribs, two complete dorsals, two more dorsal centra and a dorsal spine, some scap scraps, a partial ?pubis, a long-bone fragment and “Lump Z“, whatever that is. What you see above is my best lateral-view photograph of what I’ve designated “Cervical U”. One of these days, I’m going to do a post on how to photograph large fossils — something it’s taken me five years to get the hang of — but for today, I want to tell you about an exciting adventure with Cervical U. [Update: I wrote the How To post a few months later.]
Because my other big goal on this trip was to get it CT-scanned. Thanks to the generosity of John Hutchinson of the Royal Veterinary College, and to the help of the NHM people in arranging a loan, everything was set up for my host Vince Bickers and me to ferry the specimen up to the RVC, scan it and return it.
But first it had to be packed:
The Archbishop, Cervical U, packed and ready for transportation. Behind, Lorna Steel and Sandra Chapman of the NHM, who did the work.
Lorna and Sandra spent a long time looking for a crate big enough to pack the bone in, but came up empty — there was one that was long enough but not wide enough, one that was tall enough but not long enough, and so on. In the end we sat the bone, on its very solid plaster base, on a plastic pallet, and wrapped it in pillows, bubble-wrap and that blue stuff whose name I don’t know.
As it happened, the scan had to be delayed for a day due to lack of personnel at RVC, but Vince and I took the vertebra up on the Thursday anyway; he had to return to work on the Friday, but I took public transport to RVC for the big day. Before we went into the scanning room, John showed me his freezer room:
Just a couple of the freezers at RVC
I found it amusing that they have enough Segments Of Awesome that they have to label the various elephant-part freezers differently. And further down the aisle:
John Hutchinson proudly shows off his dead baby rhino.
Then it was off to the scanning facility, where we found that we had to unpack the vertebra: it was small enough to go through the machine, but there was no way the pallet was going through. Once we’d unpacked it and removed it, it fit pretty nicely:
The Archbishop's Cervical U all lined up and ready to go through the scanner, courtesy of John and radiographer Victoria Watts.
Because the scanner spits out X-rays in all directions, it’s controlled from a separate room, behind lead-impregnated glass:
Inside the control room
We ran three scans before we got the settings right — we needed more voltage to get through the bone and matrix than we’d first realised, and a filter was causing unhelpful moire patterns. The third scan was definitely the best, and the one I expect to be working with.
[Boring technical side-note: I plan to use 3D Slicer for visualisation thanks to Andy Farke’s series of tutorials. But, frustratingly, I wasn’t able to load the DICOM files from the scan into that program: it crashes when trying to load them (segmentation fault) even though it works fine on the ankylosaur skull that Andy walked us through in the tutorials. I fixed this by gluing the 300-odd files together into a single stack file that 3D Slicer was able to read. For the benefit of anyone else who needs to do this, the command (on a Ubuntu Linux box) was: medcon -f *.dcm -c dicom -stack3d -n -qc]
Here is an example slice, showing part of the condyle in posterior view:
CT slice through the condyle of The Archbishop's Cervical U, in posterior view. Dorsal is to the left.
The grey blobs at the bottom of the image are the plaster jacket that supports the vertebra; the white is bone, and the light grey inside it is matrix that fills the pneumatic spaces. I’m showing the condyle here because its cavities are clearly visible: further back in the vertebra, they are harder to pick out, perhaps in part because of the iron bars scattering the X-rays. It’s notable that this vertebra is less pneumatic than would be expected for a brachiosaurid — by eye, it looks like like the condyle is only 20-30% air, and this slice is not unrepresentative. Most neosauropods would be at least twice this pneumatic, so we may have an Archbishop autapomorphy here.
I’ve not yet persuaded 3D Slicer to build a 3D model for me, but I’m pleased to say that before I left RVC, John mocked up a quick-and-dirty render of the bone using only density threshholding, and I can at least show you that.
The Archbishop, Cervical U, CT scan 3d model in left ventrolateral view
Here we see the bone from the left side, previously obscured by solid plaster. From a single static image, it’s not easy to make out details, but we can at least see that there is a solid ventral floor to the centrum … and that those two crossed iron bars obscure much that we would like to see. You will get more of an idea from the rotating video that this is screencapped from.
Looking at this and comparing it with the right-lateral photo at the top of the post, it’s apparent that the density threshhold was set too high when making this model: all the bone along the lower right margin of the middle part of the centrum is good, but it’s been omitted from the model. In other words, the vertebra is more complete than this proof-of-concept model suggests. Hopefully I will shortly be able to show you a better model.
Finite Element Analysis of sauropod vertebrae
October 27, 2009
Figure 3 from Schwarz-Wings et al. 2009. A is Diplodocus, B-D are Giraffatitan.
Earlier this month Daniela Schwarz-Wings and colleagues published the first finite element analysis (FEA) of sauropod vertebrae (Schwarz-Wings et al. 2009). Above is one of the figures showing some of their results. Following standard convention, stresses are shown on a gradient with cooler colors indicating lower stresses and hotter colors indicating higher stresses. I’m not going to dwell on the on the nuts-n-bolts of FEA in general or of this study in particular. Instead, I want to talk about how sauropod vertebrae are built.
CT cross sections of BYU 12866, a mid-cervical of Brachiosaurus sp.
In cross-section, sauropod vertebrae often have thick bone at the outer edges of the laminae and in the walls and especially the floor of the centrum, as shown in this Brachiosaurus cervical. The bone everywhere else is pretty thin. If you hit one of these vertebrae with some magical forumula that would dissolve away all the bone thinner than, say, 1 cm, all that would be left would be the various apophyses, the outer margins of the laminae connecting them, and probably the bottom half of the centrum. It would be like the outline of a vertebra constructed from tent poles, or tinkertoys.
This is weird because most pneumatic sauropod vertebrae have at least something approaching an I-beam shape in cross-section. You might think that the median septum would be mechanically important, but it’s usually very thin, sometimes perforated (see Hatcher’s [1901] Diplodocus cervicals, for example), and often asymmetrically deviated to one side or the other. Not what you would expect for a piece of bone that was doing any work.
And indeed, Schwarz-Wings et al. (2009) found that:
Comparative stresses are distributed evenly around the vertebrae and mainly on the bone cortex. Peak stresses occur only at points where the tendons and muscles are inserting because the insertion areas used were small resulting in extreme localized stresses. The interior of both vertebrae is nearly stress free. Almost no stresses occur around the cavities and in their bony walls (figure 3).
This reminds me not of I-beams but of the long bones of the limbs of terrestrial vertebrates. There’s a reason why you’ve got a big honkin’ marrow cavity running through the middle of your femur: the stresses are being borne by the walls of the bone. It makes sense that vertebrae would function similarly, especially sauropod cervicals which sometimes approximate limb bones in their proportions.
So how about that median septum? Why aren’t sauropod vertebrae just hollow tubes? My guess–and it is a guess–is that they got as close to being hollow tubes as their evolutionary and developmental origins allowed. The pneumatic diverticula invaded the centra from either side and pushed in lateral-to-medial, and I think the median septum is just the wimpy little bit of bone left in between the two sets of diverticula when they almost meet up in the middle.
Even if that’s correct, there’s another mystery: why don’t the diverticula just go ahead and erode away the median septum? I can think of two possible reasons. One is that, for reasons I don’t know and I’m not sure if anyone else does either, pneumatic diverticula are good at getting into bones but pretty lousy at getting back out. There are comparatively few cases of diverticula inside bones making foramina to get out into the surrounding tissue. It does happen–in humans, the mastoid air cells sometimes bust out and make subcutaneous pneumatocoels, basically bubbles of air under the skin (Anorbe et al. 2000)–but it seems to be rare. Maybe median septa fall under the same inscrutable rule.
(Incidentally, this makes the perforate laminae in Giraffatitan all the weirder.)
Another, more mundane possibility is that the median septa (and other oddly thin bits of bone) are not never loaded, just infrequently loaded. Not enough to make them straight, thick, or normal-lookin’, but enough to make sure they don’t get resorbed entirely.
Sauropod vertebrae are just loaded with these growth-and-form-related mysteries. Kudos to Schwarz-Wings et al. for pushing us a little farther down the road toward solving them.
References
- Anorbe, E., Aisa, P. and Saenz de Ormijana, J. 2000. Spontaneous pneumatocele and pneumocephalus associated with mastoid hyperpneumatization. European Journal of Radiology 36:158–160. [abstract only for free]
- Hatcher, J.B. 1901. Diplodocus (Marsh): its osteology, taxonomy and probable habits, with a restoration of the skeleton. Memoirs of the Carnegie Museum 1: 1-63 and plates I-XIII.
- Schwarz-Wings, D., Meyer, C.A., Frey, E., Manz-Steiner, H.-R., and Schumacher, R. 2009. Mechanical implications of pneumatic neck vertebrae in sauropod dinosaurs. Proceedings of the Royal Society B. doi: 10.1098/rspb.2009.1275
Sauropods were corn-on-the-cob, not shish kebabs
June 25, 2009
This is corn on the cob:
Corn on the cob, in cross section. Stolen from http://www.istockphoto.com/file_thumbview_approve/214165/2/istockphoto_214165-co rn-cob-cross-section.jpg
This is a shish kebab:
Shish kebab. Stolen from http://www.mediterraneancafe-flatiron.com/images/shish.jpg
Most tetrapods are like shish kebabs: a whole lot of meat stuck on a proportionally tiny skeleton. If you don’t believe me, you can look at the human and cow neck torso cross-sections in Matt’s last post, or check out this ostrich-neck cross-section from his 2003 Paleobiology paper:
Ostrich neck in cross section, CT scan. From Wedel (2003a: fig. 2)
Remember that this is a freakin’ ostrich — of all extant animals, one of the ones with a most extreme long, skinny neck. And yet, if sauropods were muscled like ostriches, then their necks would have looked like this in cross section:
Putative shish kebab-style sauropod neck in cross section. Ostrich soft-tissue from Wedel (2003a: fig. 2), Diplodocus vertebra cross-section from Paul (1997: fig. 4) scaled to match size of ostrich vertebra
And soft-tissue reconstructions would have to look like this:
Diplodocus with its neck as fat as an ostrich's. Modified from Paul (1998: fig. 1F)
Which, happily, no-one is suggesting. Instead, published reconstructions of sauropod neck soft-tissue are startlingly emaciated. As exhibit A, I call this pair of Greg Paul cross-sections:
Diplodocus and Brachiosaurus neck cross-sections, showing very light musculature. From Paul (1997: fig. 4)
(Yes, the Diplodocus on the left is the one I used in the photoshopped ostrich cross-section above. It’s instructive to compare Paul’s original with the What If It Was Like A Big Ostrich version.)
Paul’s reconstructions seem to be widely considered too lightly muscled. But even the very careful and rigorous more recent reconstructions of Daniela Schwarz and her colleague show a neck much, much thinner than that of the ostrich:
Diplodocus neck cross-sections. From Schwarz et al. (2007: fig. 7a)
Although Schwarz has put a lot more soft tissue onto the neck vertebrae than Paul did, it is still a tiny proportion of what we see in extant animals — even the ostrich, remember, which has a super-thin neck compared with pretty much anything else alive today. If sauropod necks were muscled as heavily as those of, say, cows, then the soft tissue would pretty much reach down to the ground. But they weren’t: they were more like corn on the cob, with a broad core of skeleton and relatively little in the way of delicious edibles festooned about it.
So why is this? Why does everyone agree that sauropod necks were much less heavily muscled than those of any extant animal?
It’s a simple matter of scaling. A really big ostrich might have a neck 1 m long. (Actually, ostriches don’t get that big, but let’s pretend they do because it makes the maths easier). If the x meter-long neck of a sauropod was just a scaled-up ostrich neck, then it would be x times longer, x times taller and x times wider, for a total of x^3 times as voluminous and therefore x^3 times as heavy. But the cross-sectional area of the tension members that support it is only x times taller and x times wider, for a total of x^2 times the strength. In total, then, the neck’s mass/strength is x^3/x^2 = x times as great as in the ostrich. (The sauropod neck’s mass also acts further out from the fulcrum by an additional factor of x, but that is cancelled by the fact that the tension in the neck also acts x times higher above the fulcrum.)
It seems intuitively obvious (which is is code for “I have no way to prove”) that you can’t reasonably expect the neck muscles of a giant ostrich to work ten times as hard as they do in their lesser cousins, which is what you’d need to do for the 10 m neck of, say, Sauroposeidon. So simple isometric scaling won’t get the job done, and you need to restructure the neck.
But how? Surely just reducing all the muscle around the vertebrae can’t help? No indeed — but that is not really what sauropods were doing. If you look at the typical sauropod-neck life restoration, you’ll see that the proportional thickness of the neck is actually not too dissimilar to that of an ostrich — rather thicker, in fact. If you scaled an ostrich neck up to sauropod size and compared it with a real sauropod neck, you would find not that the soft tissue was too fat, but that the vertebrae were too thin.
And so we come to it at last: rather than thinking of sauropods as having reduced the amount of soft-tissue hanging on the cervical vertebrae, we do better to think of them as having kept a roughly similar soft-tissue profile to that of an an ostrich, but enlarging the vertebrae within the soft-tissue envelope. Of course if you just blindly made the vertebrae taller and wider, they would become heavier in proportion, which would defeat the whole purpose of the exercise — but as everyone who reads this blog surely knows by now, sauropod cervicals were extensively lightened by pneumaticity. By bringing air into the center of the neck, they were effectively able to displace bone, muscle and ligament away from the centre, so that they acted with greater mechanical advantage: higher epaxial tension members, lower hypaxial compression members, and more laterally positioned paraxials.
It’s a rather brilliant system — using the same volume of bone to achieve greater strength by displacing it outwards and filling the center with air (and, in doing so, also displacing soft tissue outwards). And it will be hauntingly familiar to anyone who loves birds, because it is of course exactly what birds (and pterosaurus) have done in their long bones: the hollow humeri of flying vertebrates famously allow them to attain greater strength — specifically, resistance to bending — for the same volume and mass of bone. It’s a neat trick when done with long bones, but it takes a truly awesome taxon to do it with the neck.
So maybe sauropods were not corn on the cob after all. Maybe they were Hostess Twinkies.
Hostess Twinkie. Not truly pneumatic, as the internal cavity is filled with adipose tissue rather than air, but do you have any idea how difficult it is to find good images of hollow junk food? Stolen from http://dixiedining.files.wordpress.com/2008/07/twinkie_070918_ms1.jpg
And now for something completely different
Now that I’ve finished my Ph.D at the University of Portsmouth, what am I going to do with the rest of my scientific life? I’ve always said that I have no intention of going into palaeo full time: my knowledge is far too narrow for that, so that even if paid jobs were not in insanely short supply, I wouldn’t stand much chance of getting one. And in any case, I’d hate to get into the all-too-common situation of being up against a friend for a position we both wanted. Throw in the fact that I really enjoy my computer-programming day-job and it seems pretty clear that what I need is an unpaid affiliation that lets me get on with lovely research.
Well: I am absolutely delighted to announce that, as of last month, I am an Honorary Research Associate in the Department of Earth Sciences at UCL. It’s not just that UCL is such a well-respected institution — see that Wikipedia article for some details — more importantly, it’s where Paul Upchurch hangs out, as Senior Lecturer in Palaeobiology. Sauropod fans will be familiar with Paul’s characteristically detailed and careful work, from his pioneering work on sauropod phylogeny (Upchurch 1995, 1998), through his and John Martin’s indispensible Cetiosaurus makeovers (Upchurch and Martin 2002, 2003) to the state-of-the art review that he lead-authored for Dinosauria II (Upchurch et al. 2004) and the Tokyo Apatosaurus monograph (Upchurch et al. 2005). What many of you won’t know is what an excellent collaborator he is — quick, conscientious, insightful and diplomatic. We’ve already collaborated on a few short papers (Upchurch et al. 2009 and a couple of Phylocode companion-volume chapters that are in press), and I hope there will be more in the future.
References
- Paul, Gregory S. 1997. Dinosaur models: the good, the bad, and using them to estimate the mass of dinosaurs. pp. 129-154 in: D. L. Wolberg, E. Stump, and G. D. Rosenberg (eds.), DinoFest International: Proceedings of a Symposium Sponsored by Arizona State University. Academy of Natural Sciences, Philadelphia.
- Paul, Gregory S. 1998. Terramegathermy and Cope’s Rule in the land of titans. Modern Geology 23: 179-217.
- Schwarz, Daniela, Eberhard Frey and Christian A. Meyer. 2007. Pneumaticity and soft-tissue reconstructions in the neck of diplodocid and dicraeosaurid sauropods. Acta Palaeontologica Polonica 52(1): 167-188.
- Upchurch, Paul. 1995. The evolutionary history of sauropod dinosaurs. Philosophical Transactions of the Royal Society of London Series B, 349: 365-390.
- Upchurch, Paul. 1998. The phylogenetic relationships of sauropod dinosaurs. Zoological Journal of the Linnean Society, 124: 43-103.
- Upchurch, Paul and John Martin. 2002. The Rutland Cetiosaurus: the anatomy and relationships of a Middle Jurassic British sauropod dinosaur. Palaeontology, 45(6): 1049-1074.
- Upchurch, Paul and John Martin. 2003. The anatomy and taxonomy of Cetiosaurus (Saurischia, Suaropoda) from the Middle Jurassic of England. Journal of Vertebrate Paleontology 23(1): 208-231.
- Upchurch, Paul, Paul M. Barrett and Peter Dodson. 2004. Sauropoda. pp. 259-322 in D. B. Weishampel, P. Dodson and H. Osmólska (eds.), The Dinosauria, 2nd edition. University of California Press, Berkeley and Los Angeles. 861 pp.
- Upchurch, Paul, Yukimitsu Tomida, and Paul M. Barrett. 2005. A new specimen of Apatosaurus ajax (Sauropoda: Diplodocidae) from the Morrison Formation (Upper Jurassic) of Wyoming, USA. National Science Museum Monographs No. 26. Tokyo. ISSN 1342-9574.
- Upchurch, Paul, John Martin, and Michael P. Taylor. 2009. Case 3472: Cetiosaurus Owen, 1841 (Dinosauria, Sauropoda): proposed conservation of usage by designation of Cetiosaurus oxoniensis Phillips, 1871 as the type species. Bulletin of Zoological Nomenclature 66(1): 51-55.
- Wedel, Mathew J. 2003. Vertebral pneumaticity, air sacs, and the physiology of sauropod dinosaurs. Paleobiology 29(2): 243-255.
Airheads
December 8, 2008
A 3D reconstruction of the paranasal sinuses in a human (from Koppe et al. 1999). You also have paratympanic sinuses that pneumatize the mastoid process of the temporal bone (feel for an inferiorly-directed, thumb-size protuberance right behind each ear).
An x-ray of a pig skull, from here. Can you see the outline of the brain-shaped endocranial cavity?
How about in this x-ray of a rhino skull? Image courtesy of Kent Sanders.
A sectioned cow skull. The bottom half of the endocranial cavity is exposed in the horizontal cut. The vertical cut shows the tiers of sinuses that make up most of the volume of the skull. I think that the middle tier (the large, butterfly-shaped space) is the front part of the endocranial cavity and housed the most rostral bits of the brain; note that it is completely surrounded by sinuses.
Part of a bighorn sheep skull. The pneumatic horncores of bighorns are a useful antidote to the idea that pneumatic bones must be weak.
A cross-section of an elephant skull, courtesy of Project Gutenberg. The cavity at the back marked ‘b’ is the endocranial cavity that holds the brain. The big tube running through the middle is the nasal airway. Everything else is pneumatic. Note that the brain is entirely surrounded by sinuses.
A blown skull of a proboscidean from the bone cellar at the Humbolt Museum. I snapped this on the last day in collections, on a mad scramble to get whatever non-sauropod pics (gasp!) I might want later. The bumps to the upper right are the occipital condyles; the skull is in left lateral view facing down and to the left.
Paratympanic sinuses (green) surrounding the brain (blue) of an alligator, from David Dufeau’s homepage. Go there for a lot more mind-blowing images of sinuses. The snout of this gator is filled with paranasal sinuses, they’re just not shaded in here.
Sectioned skull of a rhinoceros hornbill, which is pretty much completely filled with paranasal and paratympanic sinuses. Even the lower jaw is pneumatized.
Okay, so now you know that mammals, crocs, and birds are all air-heads. What does any of this have to do with sauropods? Well…
- Archosaurs and mammals evolved cranial pneumaticity independently. Does that mean that cranial pneumaticity is easy to evolve (since it evolved more than once) or hard to evolve (since it only evolved twice)? This is relevant to the question of how many times postcranial pneumaticity evolved.
- Archosaurs evolved cranial pneumaticity before they evolved postcranial pneumaticity. Does that mean that postcranial pneumaticity is the application of a pre-existing developmental program (bone pneumatization) to a new anatomical region (the postcranial skeleton)? Or did the developmental control of pneumatization have to evolve de novo in the postcranium?
- The development of cranial pneumatization in mammals and postcranial pneumatization in birds seems to follow similar rules. Does that mean that we can apply lessons learned from, say, the development of human sinuses to understand the development of sauropod vertebrae?
- Sauropods and big-headed mammals like elephants have this in common: at the front end they’ve got a big chunk of pneumatic bone. In sauropods, it’s the neck; in elephants, it’s the head. In both cases the big pneumatic organ makes up close to a tenth of the animal’s volume. I don’t know what else to make of that, but maybe you can get mileage out of it at a cocktail party.
I posted these because I was inspired by Darren’s post on dome-headed elephants, because they’re cool, to maybe demystify sauropod pneumaticity a little, or perhaps to re-mystify skeletal pneumatization in general. You have a pneumatic cavity between your brain and your monitor right now. How much time have you spent thinking about that (when you didn’ t have a sinus headache)?
Next time: more Berlin goodness.
UPDATE: By utter coincidence, Ohio University put out a news story about Larry Witmer’s work on sinuses yesterday. Hat tips to Yasmani Ceballos Izquierdo, who posted the link on the DML, and to Mike for sending it on to me. As long as you’re going over there, remember that Larry is one of the Good Guys and puts his papers up for public consumption; the new dino sinus paper is here. It’s great, but it makes the pictures I used here look pretty pathetic. Go have fun!
There’s almost nothing but nothing there, Brachiosaurus edition
September 3, 2008
You know, we have not done what we intended with this blog. We intended to post pretty pictures of sauropod vertebrae, sketch a few lines of text a la our inspiration, and call it good. But not one of us is capable of shutting up–me least of all–so we sit down to write 6 lines and end up writing 60 or 600.
Well, not this time. Here’s BYU 12866, probably a fifth cervical, almost certainly from Brachiosaurus, plus some CT cross-sections (the cross-sections have been straightened up a little to correct distortion in the specimen; see figure 12 here for the unexpurgated version). If they haven’t been defined before, camerae are big chambers and camellae are small chambers.
Hat tip to Mike from Ottawa for the title.
Kthxbai!
Sauropod Vertebra Picture of the Week 
