You know the drill: lotsa pretty pix, not much yap.

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Our first stop of the day was the Fruita Paleontological Area, which has a fanstastic diversity of Morrison animals, including the mammal Fruitafossor and the tiny ornithopod Fruitadens.

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Plus it’s a pretty epic landscape, especially with the clouds and broken light we had this morning.

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I found a bone! Several bits, actually, a few meters away from the Fruitadens type quarry. I’d like to think that this proximal femur might be Fruitadens, but I don’t know the diagnostic characters and haven’t had time to look them up. Anyone know how diagnostic this honorary shard of excellence might be?

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After lunch, John Foster took us on a short hike to the quarry where Elmer Riggs got the back half of the Field Museum Apatosaurus. The front half came from a site in southern Utah, several decades later.

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The locals brought Riggs out in the 1930s for the dedication of two monuments–this one at the Apatosaurus quarry, and another like it at the Brachiosaurus quarry some miles away. Tragically, both monuments have the names of the dinosaurs misspelled!

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In the afternoon we visited the Mygatt-Moore Quarry and the Camarasaurus site in Rabbit Valley. Can you see the articulated Camarasaurus neck in this photo?

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Here’s a hint: the neural arches of two posterior cervical vertebrae in transverse horizontal cross-section.

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This Camarasaurus is apparently a permanent feature. If you’re wondering why no-one has excavated it, it’s because it’s buried in sandstone that is stupid-dense. The expenditure of time and resources just isn’t worth it, when right down the hill dinosaurs are pouring out of the much softer sediments of the Mygatt-Moore Quarry like water from a hydrant. This is the lesson I am learning about the Morrison: finding dinosaurs is easy. Finding dinosaurs you can get out of the ground and prepare–that’s something else.

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Our last stop of the day was Gaston Design, where Rob Gaston showed us how he molds, casts, and mounts everything from tiny teeth to good-sized skeletons.

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Like this Deinosuchus that is about to chomp on Jim Kirkland. Jim doesn’t look too worried.

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Here’s a nice cast of a busted sauropod dorsal, probably from Apatosaurus or Diplodocus, showing the pneumatic internal structure. Compare to similar views of dorsals in this post and this one. This is actually one half of a matched set that includes both halves of the centrum. I left with one of those sets of my own, a few dollars poorer and a whole lot happier.

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The end–for now.

Illustration talk slide 47

Illustration talk slide 48

Illustration talk slide 49

Illustration talk slide 50

That last one really hurts. Here’s the original image, which should have gone in the paper with the interpretive trace next to it rather than on top of it:

Sauroposeidon C6-C7 scout

The rest of the series.

Papers referenced in these slides:

Illustration talk slide 44

Illustration talk slide 45

Illustration talk slide 46

On that last slide, I also talked about two further elaborations: figures that take up the entire page, with the caption on a separate (usually facing) page, and side title figures, which are wider than tall and get turned on their sides to better use the space on the page.

Also, if I was doing this over I’d amend the statement on the last slide with, “but it doesn’t hurt you at all to be cognizant of these things, partly because they’re easy, and partly because your paper may end up at an outlet you didn’t anticipate when you wrote it.”

And I just noticed that the first slide in this group has the word ‘without’ duplicated. Jeez, what a maroon. I’ll try to remember to fix that before I post the whole slide set at the end of this exercise.

A final point: because I am picking illustrations from my whole career to illustrate these various points, almost all fail in some obvious way. The photos from the second slide should be in color, for example. When I actually gave this talk, I passed out reprints of several of my papers and said, “I am certain that every single figure I have ever made could be improved. So as you look through these papers, be thinking about how each one could be made better.”

Previous posts in this series.

References

[This is part 4 in an ongoing series on our recent PLOS ONE paper on sauropod neck cartilage. See also part 1, part 2, and part 3.]

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Weird stuff on the ground, Big Bend, 2007.

Here’s a frequently-reproduced quote from Darwin:

About thirty years ago there was much talk that geologists ought only to observe and not theorise; and I well remember some one saying that at this rate a man might as well go into a gravel-pit and count the pebbles and describe the colours. How odd it is that anyone should not see that all observation must be for or against some view if it is to be of any service!

It’s from a letter to Henry Fawcett, dated September 18, 1861, and you can read the whole thing here.

I’ve known this quote for ages, having been introduced to it at Berkeley–a copy used to be taped to the door of the Padian Lab, and may still be. It’s come back to haunt me recently, though. An even stronger version would run something like, “If you don’t know what you’re looking for, you won’t make the observation in the first place!”

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Kent Sanders looking at scans of BYU 12613, a posterior cervical of either Kaatedocus or an anomalously small Diplodocus, at the University of Utah in May, 2008.

For example: I started CT scanning sauropod vertebrae with Rich Cifelli and Kent Sanders back in January, 1998. Back then, I was interested in pneumaticity, so that’s what I looked for, and that’s what I found–work which culminated in Wedel et al. (2000) and Wedel (2003). It wasn’t until earlier this year that I wondered if it would be possible to determine the spacing of articulated vertebrae from CT scans. So everything I’m going to show you, I technically saw 15 years ago, but only in the sense of “it crossed my visual field.” None of it registered at the time, because I wasn’t looking for it.

A corollary I can’t help noting in passing: one of the under-appreciated benefits of expanding your knowledge base is that it allows you to actually make more observations. Many aspects of nature only appear noteworthy once you have a framework in which to see them.

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BYI 12613 going through a CT scanner at the University of Utah medical center. We were filming for the “Megasaurus” episode of Jurassic CSI. That shoot was crazy fun.

So anyway, the very first specimen we scanned way back when was the most anterior of the three plaster jackets that contain the four cervical vertebrae that make up OMNH 53062, which was destined to become the holotype of Sauroposeidon. I’ve written about the taphonomy of that specimen here, and you can read more about how it was excavated in Wedel and Cifelli (2005). We scanned that jacket first because, although the partial vertebrae it contains are by far the most incomplete of the four, the jacket is a lot smaller and lighter than the other two (which weigh hundreds of pounds apiece). Right away we saw internal chambers in the vertebrae, and that led to all of the pneumaticity work mentioned above.

Sauroposeidon C5 cross section Wedel 2007b fig 14

Internal structure of a cervical vertebra of Sauroposeidon, OMNH 53062. A, parts of two vertebrae from the middle of the neck. The field crew that dug up the bones cut though one of them to divide the specimen into manageable pieces. B, cross section of C6 in posterior view at the level of the break, traced from a CT image and photographs of the broken end. The left side of the specimen was facing up in the field and the bone on that side is badly weathered. Over most of the broken surface the internal structure is covered by plaster or too damaged to trace, but it is cleanly exposed on the upper right side (outlined). C, the internal structure of that part of the vertebra, traced from a photograph. The arrows indicate the thickness of the bone at several points, as measured with a pair of digital calipers. The camellae are filled with sandstone. Wedel (2007: fig. 14).

Happily for me, that first jacket contains not only the posterior two-thirds of the first vertebra (possibly C5), but also the front end of the second vertebra. Whoever decided to plow through the second vertebra to divide the specimen into manageable chunks in the field made a savvy choice. Way back in 2004 I realized that the cut edge of the second vertebra was not obscured by plaster, and therefore the internal structure could be seen and measured directly, which is a lot cleaner than relying on the artifact-heavy CT scans. (The CT scans are noisy because the hospital machines we had access to start to pant a bit when asked to punch x-rays through specimens this large and dense.) A figure derived from that work made it into a couple of papers and this post, and appears again above.

But that’s pneumaticity, which this post is allegedly not about. The cut through the second vertebra was also smart because it left the intervertebral joint intact.

Figure 11. Fifth and partial sixth cervical vertebrae of Sauroposeidon. Photograph and x-ray scout image of C5 and the anterior portion of C6 of Sauroposeidon OMNH 53062 in right lateral view. The anterior third of C5 eroded away before the vertebra was collected. C6 was deliberately cut through in the field to break the multi-meter specimen into manageable pieces for jacketing (see [37] for details). Note that the silhouettes of the cotyle of C5 and the condyle of C6 are visible in the x-ray.

Fifth and partial sixth cervical vertebrae of Sauroposeidon.
Photograph and x-ray scout image of C5 and the anterior portion of C6 of Sauroposeidon OMNH 53062 in right lateral view. The anterior third of C5 eroded away before the vertebra was collected. C6 was deliberately cut through in the field to break the multi-meter specimen into manageable pieces for jacketing (see Wedel and Cifelli 2005 for details). Note that the silhouettes of the cotyle of C5 and the condyle of C6 are visible in the x-ray. Taylor and Wedel (2013: figure 11).

Here are a photo of the jacket and a lateral scout x-ray. The weird rectangles toward the left and right ends of the x-ray are boards built into the bottom of the jacket to strengthen it.

Figure 12. CT slices from fifth cervical vertebrae of Sauroposeidon. X-ray scout image and three posterior-view CT slices through the C5/C6 intervertebral joint in Sauroposeidon OMNH 53062. In the bottom half of figure, structures from C6 are traced in red and those from C5 are traced in blue. Note that the condyle of C6 is centered in the cotyle of C5 and that the right zygapophyses are in articulation.

CT slices from fifth cervical vertebrae of Sauroposeidon.
X-ray scout image and three posterior-view CT slices through the C5/C6 intervertebral joint in Sauroposeidon OMNH 53062. In the bottom half of figure, structures from C6 are traced in red and those from C5 are traced in blue. Note that the condyle of C6 is centered in the cotyle of C5 and that the right zygapophyses are in articulation. Taylor and Wedel (2013: figure 12).

And here’s a closeup of the C5/C6 joint, with the relevant radiographs and tracing. The exciting thing here is that the condyle is centered almost perfectly in the cotyle, and the zygapophyses are in articulation. Together with the lack of disarticulation in the cervical rib bundle (read more about that here and in Wedel et al. 2000), these things suggest to us that the vertebrae are spaced pretty much as they were in life. If so, then the spacing between the vertebrae now tells us the thickness of the soft tissue that separated the vertebrae in life.

I should point out here that we can’t prove that the spacing between the vertebrae is still the same as it was in life. But if some mysterious force moved them closer together or farther apart, it did so (1) without  decentering the condyle of C6 within the cotyle of C5, (2) without moving the one surviving zygapophyseal joint out of contact, and (3) without disarticulating the cervical ribs. The cervical ribs were each over 3 meters long in life and they formed vertically-stacked bundles on either side below the vertebrae; that’s a lot of stuff to move just through any hypothetical contraction or expansion of the intervertebral soft tissues after death. In fact, I would not be surprised if the intervertebral soft tissues did contract or expand after death–but I don’t think they moved the vertebrae, which are comparatively immense. The cartilage probably pulled away from the bone as it rotted, allowing sediment in. Certainly every nook and cranny of the specimen is packed with fine-grained sandstone now.

Anyway, barring actual preserved cartilage, this is a best-case scenario for trying to infer intervertebral spacing in a fossil. If articulation of the centra, zygs, and cervical ribs doesn’t indicate legitimate geometry, nothing ever will. So if we’re going to use the fossils to help settle this at all, we’re never going to have a better place to start.

Figure 14. Geometry of opisthocoelous intervertebral joints. Hypothetical models of the geometry of an opisthocoelous intervertebral joint compared with the actual morphology of the C5/C6 joint in Sauroposeidon OMNH 53062. A. Model in which the condyle and cotyle are concentric and the radial thickness of the intervertebral cartilage is constant. B. Model in which the condyle and cotyle have the same geometry, but the condyle is displaced posteriorly so the anteroposterior thickness of the intervertebral cartilage is constant. C. the C5/C6 joint in Sauroposeidon in right lateral view, traced from the x-ray scout image (see Figure 12); dorsal is to the left. Except for one area in the ventral half of the cotyle, the anteroposterior separation between the C5 cotyle and C6 condyle is remarkably uniform. All of the arrows in part C are 52 mm long.

Geometry of opisthocoelous intervertebral joints.
Hypothetical models of the geometry of an opisthocoelous intervertebral joint compared with the actual morphology of the C5/C6 joint in Sauroposeidon OMNH 53062. A. Model in which the condyle and cotyle are concentric and the radial thickness of the intervertebral cartilage is constant. B. Model in which the condyle and cotyle have the same geometry, but the condyle is displaced posteriorly so the anteroposterior thickness of the intervertebral cartilage is constant. C. the C5/C6 joint in Sauroposeidon in right lateral view, traced from the x-ray scout image (see Figure 12); dorsal is to the left. Except for one area in the ventral half of the cotyle, the anteroposterior separation between the C5 cotyle and C6 condyle is remarkably uniform. All of the arrows in part C are 52 mm long. Taylor and Wedel (2013: figure 14).

So, by now, you know I’m a doofus. I have been thinking about this problem literally for years and the data I needed to address it was sitting on my hard drive the entire time. One of the things I pondered during those lost years is what the best shape for a concave-to-convex intervertebral joint might be. Would the best spacing be radially constant (A in the figure above), or antero-posteriorly constant (B), or some other, more complicated arrangement? The answer in this case surprised me–although the condyle is a lot smaller in diameter than the cotyle, the anteroposterior separation between them in almost constant, as you can see in part C of the above figure.

Figure 13. Joint between sixth and seventh cervicals vertebrae of Sauroposeidon. X-ray scout image of the C6/C7 intervertebral joint in Sauroposeidon OMNH 53062, in right lateral view. The silhouette of the condyle is traced in blue and the cotyle in red. The scale on the right is marked off in centimeters, although the numbers next to each mark are in millimeters.

Joint between sixth and seventh cervicals vertebrae of Sauroposeidon.
X-ray scout image of the C6/C7 intervertebral joint in Sauroposeidon OMNH 53062, in right lateral view. The silhouette of the condyle is traced in blue and the cotyle in red. The scale on the right is marked off in centimeters, although the numbers next to each mark are in millimeters. Taylor and Wedel (2013: figure 13).

Don’t get too worked up about that, though, because the next joint is very different! Here’s the C6/C7 joint, again in a lateral scout x-ray, with the ends of the bones highlighted. Here the condyle is almost as big in diameter as the cotyle, but it is weirdly flat. This isn’t a result of overzealous prep–most of the condyle is still covered in matrix, and I only found its actual extent by looking at the x-ray. This is flatter than most anterior dorsal vertebrae of Apatosaurus–I’ve never seen a sauropod cervical with such a flat condyle. Has anyone else?

The condyle of C6 is a bit flatter than expected, too–certainly a lot flatter than the cervical condyles in Giraffatitan and the BYU Brachiosaurus vertebrae. As we said in the paper,

It is tempting to speculate that the flattened condyles and nearly constant thickness of the intervertebral cartilage are adaptations to bearing weight, which must have been an important consideration in a cervical series more than 11 meters long, no matter how lightly built.

Anyway, obviously here the anteroposterior distance between condyle and cotyle could not have been uniform because they are such different shapes. Wacky. The zygs are missing, so they’re no help, and clearly the condyle is not centered in the cotyle. Whether this posture was attainable in life is debatable; I’ve seen some pretty weird stuff. In any case, we didn’t use this joint for estimating cartilage thickness because we had no reason to trust the results.

Figure 15. First and second dorsal vertebrae of Apatosaurus CM 3390. Articulated first and second dorsal vertebrae of Apatosaurus CM 3390. A. Digital model showing the two vertebrae in articulation, in left lateral (top) and ventral (bottom) views. B-G. Representative slices illustrating the cross-sectional anatomy of the specimen, all in posterior view. B. Slice 25. C. Slice 31. D. Slice 33. E. Slice 37. F. Slice 46. G. Slice 61. Orthogonal gaps are highlighted where the margins of the condyle and cotyle are parallel to each other and at right angles to the plane of the CT slice. 'Zygs' is short for 'zygapophyses', and NCS denotes the neurocentral synchondroses.

First and second dorsal vertebrae of Apatosaurus CM 3390.
Articulated first and second dorsal vertebrae of Apatosaurus CM 3390. A. Digital model showing the two vertebrae in articulation, in left lateral (top) and ventral (bottom) views. B-G. Representative slices illustrating the cross-sectional anatomy of the specimen, all in posterior view. B. Slice 25. C. Slice 31. D. Slice 33. E. Slice 37. F. Slice 46. G. Slice 61. Orthogonal gaps are highlighted where the margins of the condyle and cotyle are parallel to each other and at right angles to the plane of the CT slice. ‘Zygs’ is short for ‘zygapophyses’, and NCS denotes the neurocentral synchondroses. Taylor and Wedel (2013: figure 15).

Kent Sanders and I had also scanned several of the smaller sauropod vertebrae from the Carnegie collection (basically, the ones that would fit in the trunk of my car for the drive back to Oklahoma). Crucially, we’d scanned a couple of sets of articulated vertebrae, CM 3390 and CM 11339, both from juvenile individuals of Apatosaurus. In both cases, the condyles and cotyles are concentric (that’s what the ‘orthogonal gaps’ are all about in the above figure) and the zygs are in articulation, just as in Sauroposeidon. These are dorsals, so we don’t have any cervical ribs here to provide a third line of evidence that the articulation is legit, but all of the evidence that we do have is at least consistent with that interpretation.

So, here’s an interesting thing: in CM 3390, above, the first dorsal is cranked up pretty sharply compared to the next one, but the condyle is still centered in the cotyle and the zygs are in articulation. Now, the vertebrae have obviously been sheared by taphonomic deformation, but that seems to have affected both vertebrae to the same extent, and it’s hard to imagine some kind of taphonomic pressure moving one vertebra around relative to the next. So I think it’s at least plausible that this range of motion was achievable in life. Using various views and landmarks, we estimate the degree of extension here somewhere between 31 and 36 degrees. That’s a lot more than the ~6 degrees estimated by Stevens and Parrish (1999, 2005). And, as we mentioned in the paper, it nicely reinforces the point made by Upchurch (2000), that flexibility in the anterior dorsals should be taken into account in estimating neck posture and ROM.

Figure 16. Dorsal vertebrae of Apatosaurus CM 11339. Articulated middle or posterior dorsal vertebrae of Apatosaurus CM 11339. A. X-ray scout image showing the two vertebrae in articulation, in left lateral view. B–D. Slices 39, 43 and and 70 in posterior view, showing the most anterior appearance of the condyles and cotyles.

Dorsal vertebrae of Apatosaurus CM 11339.
Articulated middle or posterior dorsal vertebrae of Apatosaurus CM 11339. A. X-ray scout image showing the two vertebrae in articulation, in left lateral view. B–D. Slices 39, 43 and and 70 in posterior view, showing the most anterior appearance of the condyles and cotyles. Taylor and Wedel (2013: figure 16).

Here’s our last specimen, CM 11339. No big surprises here, although if you ever had a hard time visualizing how hyposphenes and hypantra fit together, you can see them in articulation in parts C and D (near the top of the specimen). Once again, by paging through slices we were able to estimate the separation between the vertebrae. Incidentally, the condyle IS centered in the cotyle here, it just doesn’t look that way because the CT slice is at an angle to the joint–see the lateral scout in part A of the figure to see what I mean.

So, what did we find? In Sauroposeidon the spacing between C5 and C6 is 52mm. That’s pretty darn thick in absolute terms–a shade over two inches–but really thin in relative terms–only a little over 4% of the length of each vertebra. In both of the juvenile Apatosaurus specimens, the spacing between the vertebrae was about 14mm (give or take a few because of the inherent thickness of the slices; see the paper for details on these uncertainties).

Now, here’s an interesting thing: we can try to estimate the intervertebral spacing in an adult Apatosaurus in two ways–by scaling up from the juvenile apatosaurus, or by scaling sideways from Sauroposeidon (since a big Apatosaurus was in the same ballpark, size-wise)–and we get similar answers either way.

Scaling sideways from Sauroposeidon (I’m too lazy to write anymore so I’m just copying and pasting from  the paper):

Centrum shape is conventionally quantified by Elongation Index (EI), which is defined as the total centrum length divided by the dorsoventral height of the posterior articular surface. Sauroposeidon has proportionally very long vertebrae: the EI of C6 is 6.1. If instead it were 3, as in the mid-cervicals of Apatosaurus, the centrum length would be 600 mm. That 600 mm minus 67 mm for the cotyle would give a functional length of 533 mm, not 1153, and 52 mm of cartilage would account for 9.8% of the length of that segment.

Scaling up from the juveniles: juvenile sauropods have proportionally short cervicals (Wedel et al. 2000). The scanned vertebrae are anterior dorsals with an EI of about 1.5. Mid-cervical vertebrae of this specimen would have EIs about 2, so the same thickness of cartilage would give 12mm of cartilage and 80mm of bone per segment, or 15% cartilage per segment. Over ontogeny the mid-cervicals telescoped to achieve EIs of 2.3–3.3. Assuming the cartilage did not also telescope in length (i.e., didn’t get any thicker than it got taller or wider), the ratio of cartilage to bone would be 12:120 (120 from 80*1.5), so the cartilage would account for 10% of the length of the segment–almost exactly what we got from the based-on-Sauroposeidon estimate. So either we got lucky here with our tiny sample size and truckloads of assumptions, or–just maybe–we discovered a Thing. At least we can say that the intervertebral spacing in the Apatosaurus and Sauroposeidon vertebrae is about the same, once the effects of scaling and EI are removed.

Finally, we’re aware that our sample size here is tiny and heavily skewed toward juveniles. That’s because we were just collecting targets of opportunity. Finding sauropod vertebrae that will fit through a medical-grade CT scanner is not easy, and it’s just pure dumb luck that Kent Sanders and I had gotten scans of even this many articulated vertebrae way back when, since at the time we were on the hunt for pneumaticity, not intervertebral joints or their soft tissues. As Mike has said before, we don’t think of this paper as the last word on anything. It is, explicitly, exploratory. Hopefully in a few years we’ll be buried in new data on in-vivo intervertebral spacing in both extant and extinct animals. If and when that avalanche comes, we’ll just be happy to have tossed a snowball.

References

Living dead girl

Hey, look–dinosaurs!

My spouse, Vicki, the other Dr. Wedel, is a physical and forensic anthropologist. And she’s one of a very small number of scientists who have (a) learned something new about the human body, and (b) used it to help identify dead people. And since that process involves the sciences of hard-tissue histology and skeletochronology–not to mention lots of dead folks–I reckon it might be of interest here. Hence this post.

This started about a decade ago, when Vicki was working on her PhD under Alison Galloway at UC Santa Cruz. Vicki worked with Alison on a ton of forensic cases, including some you probably heard of–they analyzed the remains of Laci Peterson and her unborn baby, Connor, for Scott Peterson’s murder trial. I had the unusual privilege of assisting a couple of times, on other cases, once to take some pictures in the lab while Vicki fished the skeleton out of the bag of skin that was all that was left of the body, and once to crawl around on my hands and knees picking human finger bones out of a muddy slough near Santa Cruz. All in all, I’m happy that my usual victims have been dead a lot longer.

CT reconstruction of skull with bullet holes. Courtesy of the National Library of Medicine

CT reconstruction of skull with bullet holes. Courtesy of the National Library of Medicine

Incidentally, the only show with forensic content that Vicki will watch voluntarily is Dexter. She cannot stand CSI, NCIS, or the other “behind the scenes” forensic investigation shows. We’ve tried watching them, but the inaccuracies drive her crazy (paleo people: imagine getting the Clockwork Orange therapy and being forced to watch Clash of the Dinosaurs). Real cases are solved by teams of specialists, not two omnicompetent protagonists; it takes weeks or months, not half an hour; and if the forensics people carry guns, it’s because they know waaaay too much about how some very bad, very organized people dispose of bodies (the short answer is, not thoroughly enough*).

* Once a guy who was threatening to testify against a certain criminal organization was shot in the head, his body burned, and his burnt remains scattered along the side of the road. Vicki and Alison picked the bone shards out of the roadside gravel, identified some of them as bits of skull, and found bevelling diagnostic of ballistics trauma on some of those. The way the bone had shattered showed that the gunshot had been inflicted perimortem–around the time of death–and before the body was burned. Bottom line, whatever plan you have to get rid of the body, it is probably not going to be enough to keep someone like Vicki from figuring out how you did it. That much, the TV shows do get right.

Skull being cleaned by dermestidbeetle larvae. Image from Wikipedia.

Skull being cleaned by dermestid beetle larvae. Image from Wikipedia.

Not only is hard to really, truly get rid of a human body, it’s also hard to tell exactly when a person died, especially if all you have is a body in the woods. Insects are good–there’s a whole field of forensic entomology, whose practitioners age cadavers based on what insects are present and what stages of their life cycles they’re in. But what if all that is left is a pile of bones in the woods (which happens more often that you might think, and sometimes for completely innocuous reasons)? I’m preaching to the choir here, but bones can survive for a long time, so general wear-and-tear doesn’t tell you much. Rapetosaurus looks like it died last year.

There’s another side to this, which is figuring out how old someone was at the time of death based on their skeleton. Tooth eruption is good, and fusion of the epiphyseal growth plates, but both of those processes are basically done by the time people are in their mid-20s (teeth) to mid-30s (epiphyseal fusion). After that, there are methods based on the morphology of the auricular surface of the ilium and the public symphyses, but these only narrow things down to intervals of 5 to 15 years, and that’s a lot of missing persons reports to sift through. And none of the regular skeletal methods work past the age of 55 or 60. After that, no matter how healthy you are, the primary skeletal changes are attritional (i.e., you’re wearing out), and that process varies so much among individuals and populations that there are basically no predictive guidelines.

All of this was on Vicki’s mind when she was a grad student, so she was alert to anything that might help forensic anthropologists narrow down the possibilities for identifying dead folks. She was teaching in an osteology course and one of her students, Josh Peabody, brought up dental cementum increment analysis (DCIA), which is used in zooarcheology to determine the age and season at death of animal remains found at archaeological sites. Josh wanted to know if the method worked on humans.

Image borrowed from the University of Copenhagen.

Faunal bone from an archaeological dig. Image borrowed from the University of Copenhagen.

At the time–2004–DCIA was being tested for age at death in some historical human populations from archaeological sites, but no-one had tried using it for season at death. So Vicki and Josh set out to see if it would work.

Our teeth, like those of other mammals, are held in their sockets by periodontal ligaments. The periodontal ligament of each tooth attaches via Sharpey’s fibers to the dental cementum on the tooth root(s). Cementum is laid down in annual bands, so you can count the number of bands on a tooth, add the normal age at which that tooth erupts, and get a pretty tight estimate of when the animal died. So much for age at death, which was already being done on humans in a limited way in the early 2000s, albeit in archaeological rather than forensic contexts.

But wait, there’s more. Actually two bands of cementum are laid down every year–a dark band in the winter (roughly October to March) and a light band in the summer (roughly April to September). ‘Dark’ and ‘light’ describe the appearance of the bands under polarized light microscopy. In the summer months, the collagen fibrils that make up the cementum are aligned parallel to the tooth root, so more light comes through. In the winter, the collagen is aligned perpendicular to the root, so less light is transmitted, and the winter bands appear darker by comparison. So not only does the number of pairs of light-and-dark bands tell you the number of years since the tooth erupted, the color of the outermost band tells you in which six-month period the individual died, and the thickness of the outermost band might help you narrow that down even further.

Dental cementum increments in a human tooth, from V. Wedel (2007: figure 1).

Dental cementum increments in a human tooth, from V. Wedel (2007: figure 1).

At least, that’s how it works in other mammals. Would it hold up in humans? After all, we’re pretty good at adjusting our environments to suit us, rather than vice versa. If the winter-summer banding pattern was present in humans, it would be a huge boon to forensic science. Even people in their 40s and beyond with no very reliable skeletal indicators of age could be aged to within a year or two, and their season at death narrowed down to a 2-3 month window.

To find out, Vicki and Josh had a dentist in Santa Cruz collect 112 teeth pulled from patients over the course of a year (with full IRB approval and informed consent from the dental patients). For their purposes, a tooth pulled from a live person is just as good as one from a cadaver or skeleton–extraction kills the tooth as surely as death of the body. Better, even, in that it was easier to quickly get lots of teeth with very precise extraction data.

Vicki and Josh cut a few teeth together and they found dark and light bands right away. They presented those preliminary results at the American Academy of Forensic Sciences meeting in 2005. After that, Josh got busy with his own research, but Vicki pressed on (while finishing a dissertation on different project, and being a first-time mom).

If this was a movie, this is the part where there would be a montage of inspirational music to get us quickly past a lot of hard, boring work. Each of the 112 teeth had to be embedded in plastic, a section through the root cut out with a saw, that section mounted on a slide and ground down until it was translucent (this process will be familiar to bone histologists of all stripes, paleo or neo). Then Vicki had to go all the way around the perimeter of the each root to find the place where the cementum bands showed the most clearly, and count them. This part is trickier than it sounds, unless you’ve done some histo and know just how butt-ugly some sections can be under the scope.

The results? In the words of the Bloodhound Gang, which Vicki quotes in her DCIA talks, “You and me baby ain’t nothin’ but mammals”. Here’s the payoff graph:

Percent completion of outer cementum increment by month, from V. Wedel (2007: figure 4).

Percent completion of outer cementum increment by month, from V. Wedel (2007: figure 4).

The one out-of-place measurement was probably caused by the dark band not being thick enough to register clearly on the image.

Now that she knew that DCIA could be used to determine season at death in humans, Vicki started applying it in her forensic cases, of which there have been many. The vast majority of the work of forensic anthropologists is invisible to the public: after analyzing a set of remains, a forensic anthropologist writes a case report for whatever law enforcement office (or, much less frequently, law firm or other entity) brought them in, and that’s that. The case reports are almost always confidential, but they have to be written to exacting standards since they may be used as evidence in court. So forensic anthropologists spend a lot of time toiling over papers that hardly anyone gets to read.

However, sometimes a case is written up for journal publication–if it’s sufficiently novel or unusual, and if permission can be secured from all of the relevant parties. In 2008, Vicki was approached by the Merced County sheriff’s office to help try to identify the remains of a young woman who had been murdered in 1971. That’s the 37-year-old cold case mentioned in the title of this post, and rather than tell you about it, I’ll point you to Vicki’s case report (Wedel et al. 2013), published last month in the Journal of Forensic Identification and freely available here.

Vicki with the exhumed skeleton of Jane Doe. Photo by Debbie Noda of the Modesto Bee.

Vicki with the exhumed skeleton of Jane Doe. Photo by Debbie Noda of the Modesto Bee.

I wasn’t sure whether to post about this or not–as cool as they are, murder cases are not our normal stock in trade on this blog. What decided me was talking with Andy Farke. He read Vicki’s paper as soon as it came out, and he said that he really enjoyed getting to see how forensic anthropologists work in the real world. I sometimes take for granted that, since I am married to a forensic anthropologist, I get to see how this works all the time. But that’s a pretty rare experience–if paleontology is a small field, forensic anthropology is positively tiny. So if you want to see an example of the real science that CSI and the like are based on, here’s your window.

What’s next? Vicki has several validation studies on DCIA in progress, for which she and her collaborators have collected a much larger sample size–over 1000 teeth–to try to answer questions like: what tooth is best to use for DCIA? Should the histological sections be made longitudinally or transversely through the tooth root? Does cementum banding vary with latitude? And since banding patterns are reversed in the Southern Hemisphere, following the flip-flopped season, what happens at the equator? Watch this space, and keep an eye out for Vicki’s future publications–including a book due out next year–at her website, Bodies, Bugs, and Bones.

References

Hemisected horse head

Continuing the recent theme. We’re not giving this a “Things to Make and Do” header because the spirit of that category is to showcase anatomical preparations that average people could do in the comfort of their own homes and gardens (provided they can get hold of dead wallabies, bear skulls, etc.), and freezing and band-sawing a horse is probably outside that envelope for almost everyone (I hadn’t though of that when I posted the gator!).

In the spirit of MYDHHH:

Hemisected horse head with scale

This ain’t mine, it’s a teaching specimen from our vet school, which has a no-kill policy. All of the animal cadavers used in the anatomy labs are donated by the owners at the ends of the animals’ natural lives. So no animals were harmed in the making of this science.

But I wish it was mine. And as long as I’m dreaming, I’d like a pony. Anyone want to go halvesies?

Hemisected gator

Okay, before some wag makes this point, the gator is missing a good chunk of its tail, so this is more like the left half of the anterior two-thirds of a gator. But that would make a lousy title.

We might have more to say about this in the future, but for now, I’m going to let this 1000-word-equivalent speak for itself.

Many thanks to Elizabeth Rega for the use of the gator.

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

Earlier this month I was amazed to see the new paper by Cerda et al. (2012), “Extreme postcranial pneumaticity in sauropod dinosaurs from South America.” The title is dramatic, but the paper delivers the promised extremeness in spades. Almost every figure in the paper is a gobsmacker, starting with Figure 1, which shows pneumatic foramina and cavities in the middle and even distal caudals of Rocasaurus, Neuquensaurus, and Saltasaurus. This is most welcome. Since the 1990s there have been reports of saltasaurs with “spongy bone” in their tail vertebrae, but it hasn’t been clear until now whether that “spongy bone” meant pneumatic air cells or just normal marrow-filled trabecular bone. The answer is air cells, loads of ‘em, way farther down the tail than I expected.

Caudal pneumaticity in diplodocines. Top, transverse cross-section through an anterior caudal of Tornieria, from Janensch (1947: fig. 9). Bottom, caudals of Diplodocus, from Osborn (1899: fig. 13).

Here’s why this is awesome. Lateral fossae occur in the proximal caudals of lots of neosauropods, maybe most, but only a few taxa go in for really invasive caudal pneumaticity with big internal chambers. In fact, the only other sauropod clade with such extensive pneumaticity so far down the tail are the diplodocines, including Diplodocus, Barosaurus, and Tornieria. But they do things differently, with BIG, “pleurocoel”-type foramina on the lateral surfaces of the centra, leading to BIG–but simple–camerae inside, and vertebral cross-sections that look like I-beams. In contrast, the saltasaurines have numerous small foramina on the centrum and neural arch that lead to complexes of small pneumatic camellae, giving their vertebrae honeycomb cross-sections. So caudal pneumaticity in diplodocines and saltsaurines is convergent in its presence and extent but clade-specific in its development. Pneumaticity doesn’t get much cooler than that.

Pneumatic ilia in saltasaurines. Cerda et al. (2012: fig. 3).

But it does get a little cooler. Because the stuff in the rest of the paper is even more mind-blowing. Cerda et al. (2012) go on to describe and illustrate–compellingly, with photos–pneumatic cavities in the ilia, scapulae, and coracoids of saltasaurines. And, crucially, these cavities are connected to the outside by pneumatic foramina. This is important. Chambers have been reported in the ilia of several sauropods, mostly somphospondyls but also in the diplodocoid Amazonsaurus. But it hasn’t been clear until now whether those chambers connected to the outside. No patent foramen, no pneumaticity. It seemed unlikely that these sauropods had big marrow-filled vacuities in their ilia–as far as I know, all of the non-pneumatic ilia out there in Tetrapoda are filled with trabecular bone, and big open marrow spaces only occur in the long bones of the limbs. And, as I noted in my 2009 paper, the phylogenetic distribution of iliac chambers is consistent with pneumaticity, in that the chambers are only found in those sauropods that already have sacral pneumaticity (showing that pneumatic diverticula were already loose in their rear ends). But it’s nice to have confirmation.

So, the pneumatic ilia in Rocasaurus, Neuquensaurus, and Saltasaurus are cool because they suggest that all the other big chambers in sauropod ilia were pneumatic as well. And for those of you keeping score at home, that’s another parallel acquisition in Diplodocoidea and Somphospondyli (given the apparent absence of iliac chambers in Camarasaurus and the brachiosaurids, although maybe we should bust open a few brachiosaur ilia just to be sure*).

* I kid, I kid.**

** Seriously, though, if you “drop” one and find some chambers, call me!

Pectoral pneumaticity in saltasaurines. Cerda et al. (2012: fig. 2).

But that’s not all. The possibility of pneumatic ilia has been floating around for a while now, and most of us who were aware of the iliac chambers in sauropods probably assumed that eventually someone would find the specimens that would show that they were pneumatic. At least, that was my assumption, and as far as I know no-one ever floated an alternative hypothesis to explain the chambers. But I certainly did not expect pneumaticity in the shoulder girdle. And yet there they are: chambers with associated foramina in the scap and coracoid of Saltasaurus and in the coracoid of Neuquensaurus. Wacky. And extremely important, because this is the first evidence that sauropods had clavicular air sacs like those of theropods and pterosaurs. So either all three clades evolved a shedload of air sacs independently, or the basic layout of the avian respiratory system was already present in the ancestral ornithodiran. I know where I’d put my money.

There’s loads more interesting stuff to talk about, like the fact that the ultra-pneumatic saltasaurines are among the smallest sauropods, or the way that fossae and camerae are evolutionary antecedent to camellae in the vertebrae of sauropods, so maybe we should start looking for fossae and camerae in the girdle bones of other sauropods, or further macroevolutionary parallels in the evolution of pneumaticity in pterosaurs, sauropods, and theropods. Each one of those things could be a blog post or maybe a whole dissertation. But my mind is already thoroughly blown. I’m going to go lie down for a while. Congratulations to Cerda et al. on what is probably the most important paper ever written on sauropod pneumaticity.

References

  • Cerda, I.A., Salgado, L., and Powell, J.E. 2012. Extreme postcranial pneumaticity in sauropod dinosaurs from South America. Palaeontologische Zeitschrift. DOI 10.1007/s12542-012-0140-6
  • Janensch, W. 1947. Pneumatizitat bei Wirbeln von Sauropoden und anderen Saurischien. Palaeontographica, Supplement 7, 3:1–25.
  • Osborn, H. F. 1899. A skeleton of Diplodocus. Memoirs of the American Museum of Natural History 1:191–214.

Hello again, old friend

December 5, 2011

This week the SV-POW!sketeers are off to Bonn, Germany, for the Second International Workshop on Sauropod Biology and Gigantism. All three of us will be there, plus SV-POW! guest blogger Heinrich Mallison, plus Wedel Lab grad student Vanessa Graff, plus about 50 other awesome scientists from around the world. So we’ll have a ton of fun, but we probably won’t get much posted.

In the meantime, enjoy this cool encounter from the bone cellar at the Humboldt Museum in Berlin, where Mike and I fetched up at the end of the last IWSBG back in 2008. It’s a transversely-sectioned dorsal centrum of Giraffatitan, one that Janensch illustrated in his 1950 monograph on the vertebrae of Giraffatitan. Mike and I were very familiar with the cross-section image from the paper, so it was cool and a bit unreal to find the actual item.

Reference

Janensch, Werner. 1950. Die Wirbelsaule von Brachiosaurus brancai. Palaeontographica (Suppl. 7) 3:27-93.

Busy days. I just published a popular article on skeletal pneumaticity as a web feature at the Australian science magazine Cosmos. It’s entitled, “We are all air-heads: of sinus headaches and strangled birds”, and it includes a few things I don’t think I’ve discussed here, so hopefully even you regulars will find it a worthwhile read. I’d tell you more about it, but that would defeat the point, wouldn’t it? Go on over and check it out.

While you’re there, look at all the cool articles by award-winning science blogger and Cosmos Editorial Assistant Bec Crew, who served as my editor in this venture. I’m grateful to Bec for her help getting the article bashed into shape, her patience with my own article revision incontinence (don’t laugh, some writer you know might suffer from ARI), and most of all her enthusiasm where gory tales of science are concerned. If you’re not familiar with Bec’s work at Save Your Breath for Running Ponies, you’re in for a treat. Set your drink down first so you don’t spew it on the keyboard laughing.

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