SV-POW! is, as I’m sure you know, devoted to sauropod vertebrae. But occasionally we look at other stuff… and you might have noticed that, in recent months, we’ve been looking at, well, an awful lot of other stuff. I’m going to continue that theme here and talk about salamanders. Yeah: not sauropods, not sauropodomorphs, not saurischians, and not even dinosaurs or archosaurs. But salamanders. Don’t worry, all will become clear. This all started back in May 2010 when I blogged about amphiumas over at Tet Zoo. Amphiumas are very unusual, long-bodied aquatic salamanders.
As it happens, amphiuma vertebrae are particularly interesting if you work on saurischians because (drum-roll)… they have laminae. The term lamina is not restricted to structures present only in pneumatic saurischians: I would argue that it should be used for any sheet-like bony process on a vertebra, and I hope everyone agrees with me. Laminae are not common outside of Saurischia, but are present here and there: they’re present in stem-archosaurs (like Erythrosuchus), various crurotarsan archosaurs (including aetosaurs), some neosuchian crocodilians, and silesaurids (Desojo et al. 2002, Parker 2003, Nesbitt 2005, Wedel 2007, Butler et al. 2009). Even weirder, they’re present in Aneides lugubris, the Arboreal salamander of California and Baja California (Wedel 2007). But that’s about it.
Why would a salamander ‘want’ vertebral laminae? The laminae of the Arboreal salamander are presumed to be related to the extensive accessory ossification present in the skeleton of this animal, itself a consequence of adaptation to a peculiar climbing lifestyle. In other words, it’s hypothesised that the function (if I may be so bold as to use that word…) of the salamander’s laminae is nothing like that of the archosaurs that have them.
And now we know that A. lugubris isn’t the only salamander with laminae: amphiumas have them too. They’re clearly figured in the amphiuma literature (Gardner 2003), but (so far as I know) no-one has previously drawn attention to them when discussing archosaur laminae.
Gardner (2003) figured schematic amphiuma dorsal vertebrae that were based on a combination of features present in two of the three living amphiuma species (namely, Amphiuma means and A. tridactylum). On the lateral sides of the centra are structures that – if seen in an archosaur – would almost certainly be identified as anterior and posterior centrodiapophyseal laminae (using, as always, the nomenclature proposed by Wilson (1999)) [see the digram above, from Gardner (2003)]. There are also structures on the dorsal surfaces of the postzygapophyses that look something like laminae: they extend from the posterolateral parts of the neural arch and run across the tops of the postzygapophyses, hence recalling spinopostzygapophyseal laminae. Actually, I’ve just realised that similar structures are also sometimes present in anurans (frogs and toads) where they’ve been called paraneural crests or paraneural processes. These structures do have a ‘known’ function: in amphiumas they’re associated with complex dorsalis trunci epaxial muscles. Unlike the spinopostzygapophyseal laminae of saurischians, the structures in the amphibians are low ridges that don’t contact the neural spines, so it could be argued that they aren’t so lamina-like after all.
But what about the structures on the sides of the centra? Why are laminae present in a group of long-bodied aquatic salamanders? Why are laminae present at all? This question has been asked a few times here on SV-POW! (here, for example), and there are two primary hypotheses. One is that the laminae keep the various air sacs separate from each other, perhaps because they persist while much of the bone around them is resorbed during ontogeny, while the other is that they somehow provide mechanical support and are aligned along lines of stress (for more on this subject see the piece on finite element analysis).
The pneumaticity explanation can’t work for amphiumas (given that they’re apneumatic): does the ‘mechanical support’ one apply instead? We don’t know anything about stress distribution in amphiuma vertebrae – in fact, I don’t think we know anything about the mechanics of amphiumas at all – but it’s possible that the laminae might play this role, especially given that amphiumas have to bend, twist and push with their bodies while excavating burrows.
In conclusion, we just don’t really know what’s going on here. In fact, all we can really do at the moment is wave our arms around a bit and say “Hey, amphiumas have vertebral laminae, too”, and that’s pretty much all I’m doing here. It’s also possible that the structures I’m talking about in amphiumas are very different in detail from the vertebral laminae present in archosaurs: I’ve never even seen a single amphiuma skeletal element and am basing all of this on photos and diagrams in the literature. Nevertheless, it’s something definitely worth bringing attention to. As usual, we stand poised at the abyss, straining our eyes to see into the infinite darkness ahead.
Butler, R. J., Barrett, P. M. & Gower, D. J. 2009. Postcranial skeletal pneumaticity and air-sacs in the earliest pterosaurs. Biology Letters 5, 557-60.
Desojo, J. B., Arcucci, A. B. & Marsicano, C. A. 2002. Reassessment of Cuyosuchus huenei, a Middle–Late Triassic archosauriform from the Cuyo Basin, west-central Argentina. Bulletin of the New Mexico Museum of Natural History and Science 21, 143–148.
Gardner, J. D. 2003. The fossil salamander Proamphiuma cretacea Estes (Caudata; Amphiumidae) and relationships within the Amphiumidae. Journal of Vertebrate Paleontology 23, 769-782.
Nesbitt, S. J. 2005. Osteology of the Middle Triassic pseudosuchian archosaur Arizonasaurus babbitti. Historical Biology 17, 19–47.
Parker, W. G. 2003. Description of a new specimen of Desmatosuchus haplocerus from the Late Triassic of northern Arizona. Unpublished MS thesis, Northern Arizona University, Flagstaff, AZ, 312 pp.
Wedel, M. J. 2007. What pneumaticity tells us about ‘prosauropods’, and vice versa. Special Papers in Palaeontology 77, 207-222.
Wilson, J. A. 1999. A nomenclature for vertebral laminae in sauropods and other saurischian dinosaurs. Journal of Vertebrate Paleontology 19, 639-653.
March 23, 2010
For various arcane reasons, the SV-POW!sketeers are all neck-deep in work, so the blog may actually become somewhat more of the APOD-style picture-n-paragraph thing we originally envisioned, and less of the TetZoo-style monograph-of-the-week thing it’s often leaned toward, at least for a while.
I like it when people decorate their papers with megapixels of vertebral goodness, so here are some caudal vertebrae of the African diplodocine Tornieria, from Remes (2006:fig. 5). Click through to see the figure at its massive native resolution. And check out that pneumaticity! Really, the only question about this image is whether you can settle for just using it as your desktop background, or if you need to print out a wall-sized poster for your bedroom. So the next time you see Kristian Remes, buy him a beer for doing solid work here, on the Humbolt sauropod remount, and on pretty much everything else (including this).
Remes, K. 2006. Revision of the Tendaguru sauropod Tornieria africana (Fraas) and its relevance for sauropod paleobiogeography. Journal of Vertebrate Paleontology 26 (3): 651–669.
January 18, 2010
The last time we talked about Alamosaurus, I promised to explain what the arrow in the above image is all about. The image above is a section through the cotyle (the bony socket of a ball-and-socket joint) at the end of one of the presacral vertebra. The external bone surface would have been over on the left; it was either very thin (which happens) or a bit eroded, or both. The arrow is pointing at something weird–a plate of bone inside the vertebra that forms a sort of shadow cotyle deep to the articular surface.
This is weird for a couple of reasons. First, once camellate (small-chambered) vertebrae get above a certain level of complexity, it’s hard to make any sense of the orientation of individual bony struts. Possibly I haven’t seen enough vertebrae, or played with enough 3D models, to figure it out. You would certainly expect that the struts would be oriented to resist biomechanical loads, just like the struts in the long bones of your limbs; the fact that sauropod verts were filled with air whereas your long bones are filled with marrow shouldn’t make any difference. Back in the day, Kent Sanders–who is second author on that super-important paper on unidirectional air flow in croc lungs that you’ve probably heard about (Farmer and Sanders 2010)–speculated to me that the complex of laminae we see in the vertebrae of most sauropods are still there in the inflated-looking vertebrae of titanosaurs and birds, they’re just incarnated in internal struts rather than external laminae. Cool hypothesis for somebody to test.
The other reason that this is weird is that the plate of bone is parallel to the articular surface. One place where I have seen some regularity in terms of strut orientation is in zygapophyses, where in both camerae and camellate vertebrae the internal struts are oriented at right angles to the articular surfaces of the zygs, like beams propping up a wall. In this Alamosaurus section, there are indeed smaller struts that run at right angles to both the cotyle and the internal plate, but I have no idea why they’re so wimpy and the plate is so thick; a priori I would have expected the reverse.
It turns out that this isn’t even the first time that an internal “shadow” of the cotyle has been figured–check out this figure that I redrew from Powell’s (1992:fig. 16) Saltasaurus osteology. But don’t credit me with the discovery. I’d looked at this section a hundred times and even drawn it and never noticed the shadow cotyle, until it was pointed out by Woodward and Lehman (2009)–another reason to read that paper if you haven’t yet. Kudos to Holly Woodward for spotting this and making the connection.
Now that I’ve drawn attention to the weirdness and given credit where it’s due, this is one of those times I’m going to throw up my hands in confusion and open the floor for comments.
- Farmer, C.G., and Sanders, K. 2010. Unidirectional airflow in the lungs of alligators. Science 327:338-340.
- Powell, J.E. 1992. Osteologia de Saltasaurus loricatus (Sauropoda – Titanosauridae) del Cretacico Superior del noroeste Argentino; pp. 165-230 in J.L. Sanz and A.D. Buscalioni (editors), Los Dinosaurios y Su Entorno Biotico: Actas del Segundo Curso de Paleontologia in Cuenca. Institutio Juan de Valdes.
- Woodward, H.N., and Lehman, T.M. 2009. Bone histology and microanatomy of Alamosaurus sanjuanensis (Sauropoda: Titanosauria) from the Maastrichtian of Big Bend National Park, Texas. Journal of Vertebrate Paleontology 29(3):807-821.
January 4, 2010
Last year was good for sauropod pneumaticity. In the past few months we’ve had the publication of the first FEA of pneumatic sauropod vertebrae by Schwarz-Wings et al (2009), as well as a substantial section on pneumaticity in the big Alamosaurus histology paper by Woodward and Lehman (2009). I won’t repeat here everything that Woodward and Lehman have to say about pneumaticity, I just want to draw attention to a little piece of it. Their work is observant, up-to-date, and worth reading, so if you can get access to the paper, read it.
The major brake on the growth of our knowledge and understanding of pneumaticity is sample size. I harped on this in 2005 (Wedel 2005), and Mike just brought it up again in a comment on a previous post. In fact, what he had to say is so relevant that I’m going to just cut and paste it here:
How does degree of pneumatisation vary between individuals? Here are three more: how does it vary along the neck, how does it vary long the length of an individual vertebra, and how does it vary through ontogeny? Then of course there is variation between taxa across the tree. So what we have here is a five-and-half-dimensional space that we want to fill with observations so that we can start to deduce conclusions. Trouble is, there are, so far, 22 published observations (neatly summarised by Wedel 2005:table 7.2), which is not really enough to let us map out 5.5-space! That’s one reason why, at the moment, each observation is valuable — it adds 4% to the total knowledge in the world.
To be fair, there are a few more published observations. Schwarz and Fritsch (2006) published ASPs for cervicals of Giraffatitan and Dicraeosaurus, and I have a gnawing feeling that there are a couple here and there that I’ve seen but not remembered. I’ve got some more of my own data in the as-yet-unpublished fourth chapter of my diss, which I failed to get out as part of the Paleo Paper Challenge. And, getting back to the subject of the post, Woodward and Lehman (2009:819) have some tasty new data to report:
Digital images of sections of vertebrae and ribs were imported into ArcGIS 8.1 (Dangermond, 2001; for methods see Woodward, 2005). A unitless value for the total area of the image was calculated, using the outline of the bone as a perimeter. Subtracted from this was the area value taken up by bone, as determined by color differences (lighter areas are camellate cavities, darker areas are bone). Using this method, longitudinal sections of centra are estimated to be roughly 65% air filled. The amount of open space similarly calculated for the pneumatic proximal and medial rib sections is about 52%, whereas the cancellous spongiosa in distal rib transverse sections yields an average estimate of about 44% of their cross sectional area. Hence, the camellate cavities result in an appreciably lower bone volume compared to spongiosa.
The ASP of 0.65 for centra is right in line with the numbers I’ve gotten for neosauropods, and with the results of Schwarz and Fritsch (2006) for Giraffatitan (Dicraosaurus had a much lower ASP, around 0.2 IIRC). The stuff about the ribs is particularly interesting. Using densities of 0.95 for bone marrow, 1.8 for avian (and sauropod) compact bone, and 1.9 for mammalian compact bone we get the following:
- Pneumatic Alamosaurus vertebrae – ASP of 0.65, density of 0.63 g/cm^3.
- Pneumatic Alamosaurus ribs – ASP of 0.52, density of 0.86 g/cm^3.
- Apneumatic Alamosaurus ribs – MSP (marrow space proportion) of 0.44, density of 1.43 g/cm^3.
- Pneumatic bird long bones – ASP of 0.59, density of 0.74 g/cm^3.
- Apneumatic bird long bones – MSP of 0.42, density of 1.44 g/cm^3.
- Apneumatic mammal long bones – MSP of 0.28, density of 1.63 g/cm^3.
ASPs and MSPs of bird and mammal bones are calculated from K values reported by Cubo and Casinos (2000) for birds and Currey and Alexander (1985) for mammals. I don’t know what the in vivo density of sauropod compact bone was; changing it from the avian value of 1.8 to the mammalian value of 1.9 would have a negligible effect on the outcome.
At least with the data in hand, we can make the following generalizations:
- The apneumatic bones of birds are thinner-walled than those of mammals, on average. (This has been known for a long time.)
- The apneumatic ribs of Alamosaurus were more similar in density to apneumatic bird bones than to apneumatic mammal bones.
- In both birds and Alamosaurus, pneumatization reduces the amount of bone tissue present by 15-30% in the same elements (long bones for birds, ribs for Alamosaurus). Pneumatic bones are light not just because the marrow is replaced by air, but because there is less bone tissue than in apneumatic bones, as bird people have been observing for ages.
There’s loads more work to be done on this sort of thing, so I’m going to stop blogging now and get back to it. Stay tuned!
- Cubo, J., and Casinos, A. 2000. Incidence and mechanical significance of pneumatization in the long bones of birds. Zoological Journal of the Linnean Society 130: 499–510.
- Currey, J. D., and Alexander, R. McN. 1985. The thickness of the walls of tubular bones. Journal of Zoology 206:453–468.
- Schwarz D, and Fritsch G. 2006. Pneumatic structures in the cervical vertebrae of the Late Jurassic Tendaguru sauropods Brachiosaurus brancai and Dicraeosaurus. Eclogae Geologicae Helvetiae 99:65–78.
- 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
- Wedel, Mathew J. 2005. Postcranial skeletal pneumaticity in sauropods and its implications for mass estimates. pp. 201-228 in Wilson, J. A., and Curry-Rogers, K. (eds.), The Sauropods: Evolution and Paleobiology. University of California Press, Berkeley.
- Woodward, H.N., and Lehman, T.M. 2009. Bone histology and microanatomy of Alamosaurus sanjuanensis (Sauropoda: Titanosauria) from the Maastrichtian of Big Bend National Park, Texas. Journal of Vertebrate Paleontology 29(3):807-821.
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.
- 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.
November 26, 2009
Trying two new things this morning: grilling a turkey, and live-blogging on SV-POW!
I like to grill. Steak, chicken, kebabs, yams, pineapple, bananas–as long as it’s an edible solid, I’m up for it. But I’ve never grilled a turkey before. Neighbor, colleague, fellow paleontologist and grillmeister Brian Kraatz sent me his recipe, which is also posted on Facebook for the edification of the masses. See Brian’s excellent writeup for the whole process, I’m just going to hit the photogenic parts here. Oh, and usually I tweak any photos I post within an inch of their lives, but I don’t have time for that this morning, so you’re getting as close to a live, unedited feed as I can manage. Stay tuned for updates.
Enough of that. Let’s rock!
The process starts more than a day in advance, with the brine. Salt water, fruit, onions, garlic, spices, and some apple juice.
The turkey needs to be entirely immersed in the brine for at least 24 hours. Doing this in a solid container would require an extra big container and too much liquid to cover the bird. I follow Brian’s method of brining in a triple-layer of trash bags. You can see a turkey roaster peeking out underneath the trash bags. Helps with the carrying.
Put the turkey in the trash bags first, then pour in the brine. Unless you like huge messes.
The genius of the trash bag method on display. You can squeeze out all the air so that the volume of the bag is equal to just the turkey and the brine.
Into the fridge for a day.
First thing this morning: out come the giblets, and save the goodies from the brine. We’ll get back to the neck later.
The bird awaits.
Crucial step: putting in a drip pan. Keeps the coals off to the side for indirect heat, and catches the grease so you don’t burn down the neighborhood.
Putting in the herb butter. I used three short sticks of butter mixed with sage, lemon pepper, and Mrs. Dash. Working the skin away from the meat and then filling the space with butter was extremely nasty. This must be what diverticula feel like.
A chimney is helpful to get the coals going.
To eat is human; to grill is divine.
Smoke bombs: mesquite chips soaked in water, wrapped up in balls of tinfoil, with holes poked on top to let the smoke out.
Fruit and spices into the body cavity.
At this point, I was fairly certain that today would be the greatest day of my life. The turkey is centered over the drip pan, stuffed with goodness, subcutaneously loaded with herb butter, draped with bacon. You can see one of the smoke bombs sitting right on top of the coals.
Know what you’re getting into. This 15 lb bird just barely cleared the lid of my grill.
A little over an hour in. I installed foil heat shields to keep the wings and thighs from cooking too fast. It’s all about the indirect heat. Some of the bacon comes off now, as a mid-morning treat.
Okay, the bird is about halfway done, and I have to whip up some sustainer coals and another batch of smoke bombs. Further updates as and when. Happy Thanksgiving!
I was hoping to get some more pictures posted before we ate, but you know how it is in the kitchen on Thanksgiving Day (or, if you’re not an American, maybe you don’t know, so I’ll tell you: dogs and cats living together, we’re talking total chaos).
The turkey just before I pulled it off the grill. The heat shields turned out to be clutch, I would have completely destroyed the limbs without them. That’s going to be SOP from now on.
Ah yes, the bird, she turned out even more succulent than I hadda expected. Check out the pink shade of the meat just below the skin. I recognize that, from good barbeque, but I’ve never produced it before.
That’s it for the cooking part of today’s program. As for the ultimate fate of the bird…we ate a stupifying amount of it. I sent even more home with our guests. And the other half–yes, half–of this thunder beast is sitting in the fridge. Hello-o leftovers!
And hello-o science!
I was going to post some more pictures of the neck, but I didn’t get around to eating it, so…another time, perhaps. In lieu, here’s Mike’s turkey vertebra in left lateral view (see the original in all its supersized glory here). Note the pneumatic foramen in the lateral wall of the centrum, just behind the cervical rib loop. This is actually kind of a lucky catch; a lot of times with chickens and turkeys, the pneumatic foramina are so far up in the cervical rib loop that they can’t be seen in lateral view.
It used to freak me out a little bit that birds often don’t have their pneumatic foramina in the middle of the lateral wall of the centrum, like sauropods. But a possible explanation occurred to me just this morning as I was planning this post. I think that birds have their pneumatic foramina right where you’d expect them, based on sauropods. I’ll explain why.
The first part of the explanation is that instead of wearing their pneumatic cavities on the outside, like this Giraffatitan cervical, bird vertebrae tend to be inflated from within, with just a few tiny foramina outside. The second part is that birds have HUGE cervical rib loops compared to sauropods. If the sauropod vert shown above had its rib on, the resulting loop would be fairly dainty, the osteological equivalent of a bracelet. The cervical rib loops of birds are more like tubes, they’re so antero-posteriorly elongated.
So take the brachiosaur cervical shown above and shrink all of the external pneumatic spaces by several inches. The cavities on the arch and spine would close up entirely, and the complex of fossae and foramina on the lateral side of the centrum would be reduced to a small hole right behind the cervical rib. Then stretch out the cervical rib loop in the fore-aft direction and voila, you’d have something like a turkey cervical, with a little tiny pneumatic foramen tucked up inside the cervical rib loop.
This doesn’t explain why bird verts are inflated from within instead of being eroded from without, or why sauropods had such dinky cervical rib loops (mechanical what, now?), or why pneumatic diverticula tend to make the biggest holes in the front half of the centrum, adjacent to the cervical ribs. I just think that maybe bird and sauropod pneumaticity are not as different as they appear at first glance. Your thoughts are welcome.
November 24, 2009
I drew a couple of these a while back, and I’m posting them now both to fire discussion and because I’m too lazy to write anything new.
Here’s the neck of Apatosaurus, my own reconstruction based on Gilmore (1936), showing the possible paths and dimensions of continuous airways (diverticula) outside the vertebrae.
Here’s figure 4 from Lovelace et al. (2007), which first got me thinking about pneumatic traces on the ventral surfaces of the centra and what they might imply. You can see pneumatic spaces between the parapophyses in Supersaurus (A) and Apatosaurus (C) but not in Barosaurus (B).
This is another of my moldy oldies, again based on one of Gilmore’s pretty pictures, showing how I think the soft tissues were probably arranged. The muscles are basically the technicolor version of Wedel and Sanders (2002). Two points:
- How bulky you make the neck depends mainly on how much muscle you think was present (which of course depends on how heavy you think the neck was…). Here I was just trying to get the relationships right without worrying about bulk, but it’s worth considering.
- The volume of air inside the vertebra was dinky compared to the probable volume of air outside. In Apatosaurus, either of the canals formed by the transverse foramina has almost twice the cross-sectional area of the centrum.
A fair amount of this has been superseded with better data and prettier pictures by Schwarz et al. (2007), so don’t neglect that work in any ensuing discussion (it’s free, fer cryin’ out loud). And have a happy Thanksgiving!
- Gilmore, C.W. 1936. Osteology of Apatosaurus with special reference to specimens in the Carnegie Museum. Memoirs of the Carnegie Museum 11: 175-300.
- Lovelace, D.M., Hartman, S.A., and Wahl, W.R. 2007. Morphology of a specimen of Supersaurus (Dinosauria, Sauropoda) from the Morrison Formation of Wyoming, and a re-evaluation of diplodocid phylogeny. Arquivos do Museu Nacional, Rio de Janeiro 65(4):527-544.
- Schwarz, D., Frey, E., and Meyer, C.A. 2007. Pneumaticity and soft−tissue reconstructions in the neck of diplodocid and dicraeosaurid sauropods. Acta Palaeontologica Polonica 52 (1): 167–188.
- Wedel, M.J., and Sanders, R.K. 2002. Osteological correlates of cervical musculature in Aves and Sauropoda (Dinosauria: Saurischia), with comments on the cervical ribs of Apatosaurus. PaleoBios 22(3):1-6.
Mike asked me to add the labeled version of Nima’s brachiosaur parade, so here you go. Click to embiggen.
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.)
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:
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:
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:
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:
Because the scanner spits out X-rays in all directions, it’s controlled from a separate room, behind lead-impregnated glass:
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:
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.
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.
July 20, 2009
Weren’t we just discussing the problem of keeping up with all the good stuff on da intert00bz? The other day Rebecca Hunt-Foster, a.k.a. Dinochick, posted a “mystery photo” that is right up our alley here at SV-POW!, but, lazy sods that we are, we missed it until just now. Here’s the pic:
I flipped it 90 degrees so that you can see more clearly what is going on. This is a cut and polished section of a pneumatic sauropod vertebra–the bottom half of the mid-centrum of a dorsal vertebra, to be precise. Cervicals usually have concave ventral surfaces, and sacrals are usually either wider and flatter or narrower and V-shaped in cross sections, so I am pretty confident that this slice is from a dorsal. Compare to the classic anchor cross-section in this Camarasaurus dorsal:
(You may remember this image from Xenoposeidon week–almost two years ago now!)
As usual, bone is black, air is white, and everything else is gray. And the ASP is:
461080 white pixels/(461080 white + 133049 black pixels) = 0.78
So, we know what this is, and we know the ASP of this bit of it, and we can even figure out the in vivo density of this bit. The density of cortical bone ranges from about 1.8 g/cm^3 for some birds to about 2.0 for most mammals. For the sake of this example–and so I can hurry back to writing my lecture about the arse–let’s call it 1.9. The density is then the fraction of bone multiplied by the density of bone, full stop. If it was an apneumatic bone, we’d have to add the fraction of marrow multiplied by the density of marrow, but the density of air is negligible so we can skip that step here. The answer is 0.22 x 1.9 = 0.42 g/cm^3, which is pretty darned light. Keep in mind, though, that some slices of Sauroposeidon (and ‘Angloposeidon’, as it turns out) have ASPs of 0.89, and thus had an in vivo density half that of the above slice (0.11 x 1.9 = 0.21 g/cm^3).
What’s that in real money? Well, your femora are roughly 60% bone and 40% marrow, with a density of ((0.6 x 2.0)+(0.4 x 0.93)) = 1.6 g/cm^3, four times as dense as the bit of vertebra shown above, and eight times as dense as some slices of Sauroposeidon and ‘Angloposeidon’. If that doesn’t make you self-conscious about your heavy thighs, I don’t know what will.
Yes, that was a lame joke, and yes, I’m going out on it.
Hat tip to Dinochick.
P.S. It’s the 40th anniversary of the first moon landing today. Hoist a brew for Neil and Buzz, wouldja?
July 18, 2009
By now you’ll recognize this as NHM 46870, a minor celebrity in the world of pneumatic sauropod vertebrae. Darren has covered the history of the specimen before, and in the last post he showed photographs of both this chunk and its other half. He also briefly discussed the Air Space Proportion (ASP) of the specimen, and I’ll expand on that now.
People have mentioned the weight-saving properties of sauropod vertebrae from the very earliest discoveries of sauropods. But as far as I know, no one tried to quantify just how light they might have been until 2003.
That fall I was starting my third year of PhD work at Berkeley, and I was trying to think of everything that could possibly be investigated about pneumaticity in sauropod vertebrae. I came up with a list of four things:
- external traces of pneumaticity (foramina, fossae, tracks, laminae)
- form and complexity of internal spaces (camerae, camellae, branching patterns)
- ratio of bone to air space within a pneumatic element
- distribution of postcranial skeletal pneumaticity (PSP) in the body
That list of four things formed the outline for my first dissertation chapter (Wedel 2005), and for my dissertation itself. In fact, all of my papers that have anything to do with pneumaticity can be classified into one or more of those four bins:
- external traces: Wedel (2005, 2007)
- internal complexity: Wedel et al. (2000a, 2000b), Wedel (2003b)
- bone/air ratio: Wedel (2005)
- distribution in the body: Wedel (2003a, 2006, 2009)
That list is not exhaustive. It’s every aspect of PSP that I was able to think of back in 2003, but there are lots more. For example, I’ve only ever dealt with the internal complexity of sauropod vertebrae in a qualitative fashion, but the interconnections among either chambers or bony septa could be quantified, as Andy Farke has done for the frontal sinuses of hartebeests (Farke 2007). External traces on vertebrae and the distribution of PSP in the body can also be quantified, and were shortly after I drew up the list–see Naish et al. (2004) for a simple, straightforward approach to quantifying the extent of external pneumatic fossae, and O’Connor (2004, 2009) for a quantitative approach to the extent of pneumaticity in the postcranial skeletons of birds. There are undoubtedly still more parameters waiting to be thought of and measured. All of these papers are first steps, at least as applied to pneumaticity, and our work here is really just beginning.
Also, it took me an embarrassingly long time to “discover” ASPs. I’d had CT slices of sauropod vertebrae since January, 1998, and it took me almost six years to realize that I could use them to quantify the amount of air inside the bones. I later discovered that Currey and Alexander (1985) and Casinos and Cubo (2000) had done related but not identical work on quantifying the wall thickness of tubular bones, and I was able to translate their results into ASPs (and MSPs for marrow-filled bones).
The procedure is pretty simple, as Mike has shown here before. Open up the image of interest in Photoshop (or GIMP if you’re all open-sourcey, like we are), make the bone one color, the air space a second color, and the background a third color. Count pixels, plug ‘em into a simple formula, and you’ve got the ASP. I always colored the bone black, the air space white, and the background gray, so
ASP = (white pixels)/(black + white pixels)
For the image above, that’s 460442/657417 = 0.70.
Two quick technical points. First, most images are not just black, white, and one value of gray. Because of anti-aliasing, each black/white boundary is microscopically blurred by a fuzz of pixels of intermediate value. I could have used some kind of leveling threshold thing to bin those intermediate pixels into the bone/air/background columns, but I wanted to keep the process as fast and non-subjective as possible, so I didn’t. My spreadsheet has columns for black, white, gray, and everything else. The everything else typically runs 1-3%, which is not enough to make a difference at the coarse level of analysis I’m currently stuck with.
Second, I prefer transverse sections to longitudinal, because most of the internal chambers are longitudinally oriented. That means that longitudinal sections, whether sagittal or horizontal, are likely to cut through a chamber wall on its long axis, which makes the walls look unnaturally thick. For example, in the image above the median septum looks 5-10 times thicker than the outer walls of the bone, which would be a first–usually the outer walls are thicker than the internal septa, as you can see here. I don’t think the median septum really is that thick; I strongly suspect that a very thin plate of bone just happened to lie in the plane of the cut. It takes some work to get used to thinking about how a 2D slice can misrepresent 3D reality. When I first started CT scanning I was blown away by how thick the bone is below the pre- and postzygapophyses. I was thinking, “Wow, those centrozygapophyseal laminae must have been way more mechanically important than anyone thinks!” It took me a LONG time to figure out that if you take a transverse slice through a vertical plate of bone, it is going to look solid all the way up, even if that plate of bone is very thin.
Even apart from those considerations, there is still a list of caveats here as long as your arm. You may not get to choose your slice. That’s almost always true of broken or historically sectioned material, like NHM 46870. It’s even true in some cases for CT scans, because some areas don’t turn out very clearly, because of mineral inclusions, beam-hardening artifacts, or just poor preservation.
The slice you get, chosen or not, may not be representative of the ASP of the vertebra it’s from. Even if it is, other elements in the same animal may have different ASPs. Then there’s variation: intraspecific, ontogenetic, etc. So you have to treat the results with caution.
Still, there are some regularities in the data. From my own work, the mean of all ASP measurements for all sauropods is about 0.60. That was true when I had only crunched my first six images, late on the evening of October 9, 2003. It was true of the 22 measurements I had for Wedel (2005), and now that I have over a hundred measurements, it’s still true. More data is not shifting that number at all. And Woodward (2005) and Schwartz and Fritsch (2006) got very similar numbers, using different specimens.
This is cool for several reasons. It’s always nice when results are replicated–it decreases the likelihood that they’re a fluke, and in this case it suggests that although the limitations listed above are certainly real, they are not deal-killers for answering broad questions (we are at this point seeing the forest more clearly than the trees, though).
More importantly, the mean 0.60 ASP for all sauropod vertebrae is very similar to the numbers that you get from the data of Currey and Alexander (1985) and Cubo and Casinos (2000): 0.64 and 0.59, respectively. So sauropod vertebrae were about as lightly built as the pneumatic long bones of birds, on average.
Naturally, there are some deviations from average. Although I didn’t have enough data to show it in 2005, brachiosaurids tend to have higher ASPs than non-brachiosaurids. And Early Cretaceous brachiosaurids from the US and England are especially pneumatic–the mean for all of them, including Sauroposeidon, ‘Angloposeidon’, some shards of excellence from the Isle of Wight, and assorted odds and ends, is something like 0.75-0.80, higher even than Brachiosaurus. So there’s probably a combined phylogenetic/functional story in there about the highly pneumatic, hyper-long-necked brachiosaurids of the Early Cretaceous of Laurasia. Another paper waiting to be written.
Here’s another shard of excellence, referred to Chondrosteosaurus, NHM R96. As Mike had discussed here before, there’s no good reason to believe that it actually is Chondrosteosaurus, and the internal structure looks considerably more subdivided than in NHM 46870. This is an anterior view, and normally you’d be seeing a nice hemispherical condyle, but all of the cortical bone is gone and the internal structure is revealed. The little black traces are bone and the brownish stuff is rock matrix filling the pneumatic cavities.
A few years ago, Mike asked me to look at that photo and guess the ASP, and then run the numbers and see how close I got. I guessed about 78%, then did the calculation, and lo and behold, the answer was 78%. So I’m pretty good at guessing ASPs.
Except I’m not, because as any of you armed with photo software can tell, that picture has 24520 black pixels and 128152 white ones, so the ASP is actually 128152/(128152+24520) = 0.84. The moral of the story is check your homework, kids! Especially if you seem to be an unnaturally good estimator.
ASP-ESP aside, I think ASP is cool and has some interesting potential at the intersection of phylogeny and biomechanics. But the method is severely limited by sample size, which is severely limited by how much of a pain in the butt preparing the images is. In most cases you can’t just play with levels or curves to get a black and white image that faithfully represents the morphology, or use the magic wand, or any of the other myriad shortcuts that modern imaging programs offer. Believe me, I’ve tried. Hard. But inevitably you get some matrix with the bone, or some bone with the matrix, and you end up spending an impossible amount of time fixing those problems (note that this is not a problem if you use perfect bones from extant animals, which is sadly not an option for sauropod workers). So almost all of my ASP images were traced by hand, which is really time-consuming. I could pile up a lot more data if I just sat around for a few weeks processing images, but every time I’ve gotten a few free weeks there has been something more important demanding my attention, and that may always be the case. Fortunately I’m not the only one doing this stuff now, and hopefully in the next few years we’ll get beyond these first few tottering steps.
Side Note: Does NHM 46870 represent a juvenile, or a dwarf?
This came up amongst the SV-POW!sketeers and we decided it should be addressed here. Darren noted that the vert at top is pretty darned small, ~23 cm for the preserved part and probably only a foot and a half long when it was complete, which is big for an animal but small for a sauropod and dinky for a brachiosaurid (if that’s what it is). Mike made the counter-observation that the internal structure is pretty complex, citing Wedel (2003b:fig. 12) and surrounding text, and suggested that it might be an adult of a small or even dwarfed taxon. And I responded:
I’m not at all certain that it is dwarfed. It matters a lot whether the complex internal structure is polycamerate or camellate. I was agnostic for a long time about how different those two conditions are, but there is an important difference that is relevant in this case: the two internal structures develop differently. Polycamerate verts really do get progressively more complex through development, as illustrated–there are at least two great series that show this, that I need to publish one of these days. But I think camellate vertebrae may be natively complex right from the get-go; i.e., instead of a big simple diverticulum pushing in from the side and making a big camera first, a bunch of smaller diverticula may remodel the small marrow spaces into small air spaces with no prior big cavities. At least, that’s how birds seem to do it. This needs more testing from sauropods–a good ontogenetic sequence from Brachiosaurus would be clutch here–but it’s my working hypothesis. In which case NHM 46870 may be a juvenile of a camellate taxon, rather than an adult of a polycamerate taxon.
The whole camerate-vs-camellate problem deserves a post of its own, and this post is already too long, so we’ll save that for another day.
- Cubo, J., and Casinos, A. 2000. Incidence and mechanical significance of pneumatization in the long bones of birds. Zoological Journal of the Linnean Society 130: 499–510.
- Currey, J. D., and Alexander, R. McN. 1985. The thickness of the walls of tubular bones. Journal of Zoology 206:453–468.
- Farke, A. A. 2007. Morphology, constraints, and scaling of frontal sinuses in the hartebeest, Alcelaphus buselaphus (Mammalia: Artiodactlya, Bovidae). Journal of Morphology 268:243-253.
- Naish, D., Martill, D. M., Cooper, D. & Stevens, K. A. 2004. Europe’s largest dinosaur? A giant brachiosaurid cervical vertebra from the Wessex Formation (Early Cretaceous) of southern England. Cretaceous Research 25:787-795.
- O’Connor, P.M. 2004. Pulmonary pneumaticity in the postcranial skeleton of extant Aves: a case study examining Anseriformes. Journal of Morphology 261:141-161.
- O’Connor, P. M. 2009. Evolution of archosaurian body plans: Skeletal adaptations of an air-sac-based breathing apparatus in birds and other archosaurs. Journal of Experimental Zoology DOI: 10.1002/jez.548
- Schwarz D, Fritsch G. 2006. Pneumatic structures in the cervical vertebrae of the Late Jurassic Tendaguru sauropods Brachiosaurus brancai and Dicraeosaurus. Eclogae Geologicae Helvetiae 99:65–78.
- Woodward, H. 2005. Bone histology of the titanosaurid sauropod Alamosaurus sanjuanensis from the Javelina Formation, Texas. Journal of Vertebrate Paleontology 25 (Supplement to No. 3):132A.