Tutorial 13: how to dissect a neck
March 30, 2011
This tutorial is based on all the things that I stupidly forgot to do along the way of tearing down the juvenile giraffe neck that Darren, John Conway and I recently got to take to pieces. At half a dozen different points in that process, I found myself thinking “Oh, we should have done X earlier on!” So it’s not a tutorial founded on the idea that I know how this should be done; it’s about how I am only now realising how it should be done, off the back of my dumb mistakes.
Cervical vertebra 5 of two-week-old giraffe: left column, anterior; middle column, top to bottom, dorsal, left lateral, posterior, all with anterior to the left; right column, posterior
What you want is to get the maximum possible information out of your specimen. At each stage of preparation, information is lost — a necessary evil, because of course at the same time new information becomes available. So don’t miss anything early on.
The whole neck
If you’re lucky, you’ll get the complete, intact neck to work with. (Ours was not quite intact, having been skinned, and lost an indeteminate amount of superficial muscle and ligament in the process.) So before you start cutting, photograph the neck in dorsal, ventral, lateral, anterior and posterior aspects.
Next, you want to measure the neck:
- total mass
- total length, front of atlas to back of last centrum.
- maximum flexion (i.e. downwards bend)
- maximum extension (i.e. upwards bend)
- maximum deflection (i.e. lateral bend)
These last three are hard to do, because “maximum” flexion, extension and deflection are not exact things. You can always push or squeeze or bend a bit harder. These are the unpleasantly messy aspects of working with animals rather than robots — most kinds of tissue are flexible and resilient. You just have to do the best you can, and supplement your measurements with photographs of the neck bent in each direction.
Skinning
Now you’re ready to start taking that baby apart. Get the skin off, then redo all your photos and redo all your measurements — yes, even total length, even though you “know” removing the skin can’t affect that. Because you don’t know what you don’t know. Does removing the skin affect the maximum range of movement? How much of the neck’s total mass was due to the skin? Weigh the skin as well: does its mass added to that of the deskinned neck add up to that of the intact neck? If not, is the discrepancy due to blood loss?
Stripping muscle
Once the skin is off, you can start removing muscles. Ideally, you want to identify each muscle as you go, and remove them one by one, so that you leave the major ligaments behind. In practice this is harder than it sounds, because the muscles in real necks are, inconveniently, not clearly delineated and labelled like the ones in books. Still, going slowly and carefully, it’s often possible to avoid cutting actual muscles but just the fascia between them, which allows you remove complete muscles. Done well, this can leave in place not only the nuchal ligament running along the top of all the neural spines, but the shorter ventral ligaments joining adjacent vertebrae.
John (left) and Darren (right) removing muscle from the giraffe neck (in right lateral aspect), while keeping ligaments intact
As you’re doing this, you want to avoid damaging the intercentral joints and the zygapophyseal capsules, so far as possible. You’ll probably find it easy to preserve the former, which are tough, but harder not to accidentally damage at least some of the latter. You want to keep them intact as far as possible, so you can see how the react when you manipulate the neck. (Do these manipulations gently, or you’ll tear those capsules.)
Now that the skin and muscles are both off — at least, so far as you can remove the muscles, which will not be completely — you can redo all your photos and redo all your measurements again. Yes, all of them. Because you just can’t tell what you’re going to be interested in later, and curse yourself for missing.
Stripping ligament
Go right ahead. Remove the short ligaments, and do your best to get the nuchal ligament off all in one chunk — not quite as easy as it sounds, because it doesn’t just sit on top of the neural spines, but sort of encloses them. Measure the nuchal ligament at rest, then stretch it out as far as you can and measure it extended. Calculate how far it stretched as a proportion of the rest length. Compare this with what you learned from Alexander (1989:64-65). Hmm. Interesting, no?
You can guess what’s coming now: redo all your photos and redo all your measurements yet again. You should find that the total length is the same, but who knows what you might find about changing flexibility? Also, your progressive sequence of mass measurements will tell you what proportion of the whole neck was skin, muscle, ligament, etc.
Separating the vertebrae
This sounds like it should be easy, but it’s not. The zygapophyses will come apart very easily, but the centra will be held firmly together with very dense connective tissue which has be cut carefully away, piece by piece, with the blade of a scalpel worked between the condyle of one vertebra and the cotyle of the next. (I’m writing here about a giraffe neck, but I’m confident the same will be true of other artiodactyls and maybe most mammals; bird necks are different.)
Once you’ve got the vertebrae separate, photograph each vertebra separately, from each of the cardinal directions. Also, measure each vertebra separately — especially for centrum length, but you may as well get all the major measurements. These measurements will include the cartilage caps at the front and back of each centrum. (This is the step that I most regret missing out.)
Articulate the vertebrae in “neutral pose” by keeping the centra in full contact and rotating each intercentral joint about its midpoint until the corresponding zygapophyses are maximally overlapped. What does this pose look like? How does it compare to the animal’s habitual pose in life? (If possible, compare with the pose shown by an X-ray of the live animal, since necks lie.)
Articulate the vertebrae in positions of “maximal” flexion, extension and deflection by keeping the centra in full contact and rotating each intercentral joint about its midpoint until the corresponding zygapophyses are displaced to a degree of your choosing. Try it with the zygs allowed to slide until they are 50% disarticulated, then with 75% disarticulation, then displacing until they are just past the point of contacting each other. Photograph all these poses and measure their deflection. Compare these variant poses with those obtained when the vertebrae were still joined together, and when the ligaments, muscles and skin were still in place. What degree of zygapophyseal disarticulation best matches the whole-neck bending ability? How does this vary along the neck? How does that this compare with what you may have been led to expect in the literature. Hmm.
Using your earlier photos of the whole neck’s bending profile, arrange the vertebrae in the exact same pose. How much do the zygapophyses disarticulate in these poses? As you rotate the joints about the articulation of their centra, do the zygs just slide neatly past each other, or do they move far apart from each other as the neck bends? Interesting, yes?
Cleaning the vertebrae
Have you recorded all the information you need from the intact vertebrae with their cartilage in place? If you’re sure, then …
Lightly simmer the vertebrae for an hour or so, then remove the excess flesh by hand and using a toothbrush. Repeat as needed to get them clean. If you can do this really carefully — I couldn’t — you may be able to keep the cartilage firm, and firmly articulated with the bone. (Bugging the vertebrae is probably a better approach for this purpose, but I find it hard to be that patient.)
Once the vertebrae have dried out — and especially, once their cartilage is dry — re-measure each vertebra. Does the drying of the cartilage affect the centrum length?
Simmer the vertebrae again and gently peel off the cartilage caps at the front and back of each centrum. Re-measure the centra: how long are they now? What proportion of each centrum’s length was cartilage?
Articulate all the centra in a straight line, and measure the total length. How does this compare with the whole-neck length you started with? [Crib-sheet answer for our baby giraffe: 41 cm vs. a whole-neck length of 51 cm. Expect a closer match if you’re dealing with an adult animal,which will have proportionally less cartilage.]
Articulate the vertebrae in “neutral pose” as you did back when the individual vertebrae were complete. How does the new “neutral pose” compare with the old one? With habitual life posture? Huh. Makes you think, doesn’t it?
Nearly done …
Articulate the vertebrae in positions of “maximal” flexion, extension and deflection as you did before, and compare your results with those from when the vertebrae were complete with their cartilage caps. Well! Who’d have thought?
Now remember that the fossils we have of, say, sauropod cervicals are those of the dry bone only, with no cartilage. Think about how different the “neutral pose” and range of movement would be if we had the intact vertebrae with their cartilage.
Dammit all, I’ve given the game away
As I wrote this article, I found myself giving away more and more of a paper I’ve been planning to write, in which I go through essentially this process with a couple of necks, ideally from very different clades, and write up the results. Say, a giraffe, an ostrich and a croc. The extent to which the dry-bone postures and flexibility vary from those of the live animals would give us a reasonable starting point for thinking about how life postures and flexibility of sauropods might have varied from what we’d deduce from the dry bones alone.
Wouldn’t that be a great little paper?
Well, I might still write it when I find the time, but I won’t stand in the way of anyone else who wants to plough straight in and just get it done. (You might mention me in the acknowledgements if you do.)
In a comment on the previous post, Dean asked: “What was the difference in length between the neck with its cartilage and the bones flush together?”
I’m glad you asked me that. You’ll recall from last time that the fully fleshed neck — intact apart from the removal of the skin and maybe some superficial muscle — was 51 cm in length from the front of the atlas to the back of the centrum of the seventh cervical vertebra. When I pose the cleaned and cartilage-free bones together, the total length of the series is only 41 cm — 10 cm shorter, coming in at just over 80% of the live length. Don’t believe me? Here are the photos!
I’m sure I need hardly say, but the top image is the neck as we got it, the second is the cleaned bones posed in more or less the arrangement they must have been in life (both of these taken from the previous post) and the bottom image the bones fully abutting.
So! The neck of Wallace the baby giraffe was very nearly a quarter as long again as the bones alone suggest. Does this mean that the neck of Giraffatitan was really 10.6 m long instead of 8.5 m?
It’s an exciting prospect, but I’m afraid the answer is no. As I hinted last time, while it’s perfectly acceptable, indeed obligatory, to recognise the important role of cartilage in sauropod necks qualitatively, we can’t blindly apply the numbers from Wallace the baby giraffe to adult sauropods for two reasons: 1, Wallace is a baby; and 2, Wallace is a giraffe.
The first of these reasons is part of why I am keen to do this all over again with an adult giraffe when I get the opportunity; but there’s not much we can do about the second. One might think that a more closely related extant animal such as an ostrich might have a neck that is more homologous with those of sauropods; and that’s true, but my feeling is that the giraffe is more analogous. That is, although the birds share more recent common ancestry with sauropods, giraffes’ more similar size seem to have encouraged them to evolve cervicals that are in some ways more similar to those of sauropods, most notably in the possession of ball-and-socket intervertebral joints rather than the saddle-shaped joints that are ubiquitous in birds.
How big a deal is Wallace’s juvenile status? Well, take a look at his fifth cervical vertebra in posterior view:
If this bone were found in 150 million years by competent palaeontologists, in a world where there were no extant artiodactyls to compare with, what would they make of it? Most of the articular area of the centrum is very obviously damaged, exposing the internal spongy texture of cancellous bone — presumably the bone surface was attached more firmly to the cartilaginous posterior end of the element than to the inner part of the bone, so it came away with the cartilage during simmering. So it would be obvious to our future palaeontologists that the articular surface was missing, and that the complete vertebra would have been somewhat longer — but it would be hard to judge by how much.
But the state of this bone is particularly interesting because the middle part of the centrum does have a preserved bone surface. It would be easy to extrapolate that out across the whole area of the posterior end of the centrum, and assume that this was the maximum posterior extent of the element’s functional length in life — an assumption that we know, having taking the neck apart ourselves, would be completely wrong.
Are we making similar incorrect assumptions with our sauropod vertebrae?
An even more interesting case is the postzygapophyses. The posterodorsal surface of the left postzyg is slightly damaged, but the bone of the right postzyg has a nice, perfectly preserved surface. But I can tell you that the functional articular surface of the postzyg was totally different from this: different size, different shape, different position, different orientation. If we tried to calculate range of movement from these zygapophyseal facets, the results we got would be literally meaningless.
The good news is, there’s a clue that would prevent us from making this mistake — a really nice, obvious one. The texture of the bone on the postzyg is irregularly crenellated in a way that strongly indicates a cartilaginous extension: it’s the same texture you see on the ends of the long-bones of (even mature) birds if you peel off the cartilage caps. (It’s also what you see, at a much bigger scale, on the ends of the sauropod long-bones.)
But while the presence of this texture indicates the presence of cartilage, I don’t know whether the converse is true. In the absence of such a texture, can we assume the absence of cartilage? I just don’t know. Anyone?
Things to Make and Do, part 8: baby giraffe neck
March 24, 2011
Back in early Februrary, Darren and I got an email out of the blue from biomechanics wizard and all all-round good guy John Hutchinson, saying that he’d obtained the neck of a baby giraffe — two weeks old at the time of death — and that if we wanted it, it was ours.
Of course, the timing wasn’t great for me — Brontomerus day was coming up fast, and the final publicity arrangements were buzzing around like crazy, so it wasn’t possible to go and fetch the neck right then. But John had an even better proposition: that he could keep the neck frozen, and we could come to the Royal Veterinary College and dissect it on site. As soon as I’d established with Darren that I’d get to be the one to keep the bones when the dissection was done, we enthusiastically agreed, and booked a date with John. [The photo here shows a baby giraffe, not the one that we had — note that the neck is proportionally much shorter than in an adult.]
And so it was that on Wednesday 9th March, I drove up from Ruardean to Potter’s Bar and picked up Darren and pterosaur-jockey John Conway from the railway station. From there, we found our way to the RVC campus easily enough, with only the statutory minimum number of times getting lost (once).
The bad news was that the neck had already been skinned before it made its way to the RVC. We don’t know why, by whom, or when, and more importantly we don’t know how much of the other soft tissue was removed in the process — for example, the trachea and oesophagus were gone — along with, we assume, the recurrent laryngeal nerve that Matt had asked us to look out for — and we wonder whether our nuchal ligament was complete. (That is the long ligament that runs along the top of the neck and helps to prevent it from sagging.)
But anyway, here is our baby, in left lateral view, as it came out of its plastic sack, measuring a healthy 51 cm in length.
Like so many specimens, at this point it really looks like an undifferentiated blob of gloop. There are a couple of things to look for, though.
On the left of the picture, you’ll see that the terminal 10% or so is well separated from the rest, ahead of of portion of exposed bone. That bone is the anterior margin of the axis (i.e. the second cervical vertebra). The atlas (first cervical) is still encased in soft tissue at this point, but could be moved around fairly freely, including twisting.
On the right, and you’ll probably need to click through to see this, is a strange metal pin, stuck right into the back of C7. This was firmly embedded and we never figured out what it was, or what it was doing there. As you’ll see in the photos below, I’ve allowed it to stay in place, even in the final prepared vertebrae. If anyone knows what it is, do tell!
I took a bunch of photos and measurements before we ploughed in, but I am ashamed to say that I failed to get many, many of the images and numbers that I should have. Even allowing for the fact that the specimen was not intact when we got it, we and particularly I fumbled the ball badly. So much so that I will shortly publish a tutorial on How To Dissect A Neck which will be based primarily on what we failed to do.
I suppose it’s true that we only ever learn from mistakes. The trick is to learn from other people’s, rather than going through the frustrating and expensive process of making your own. Oh well. Next time, for sure.
Here we have John (left) and Darren (right) hard at work teasing away the long epaxial muscles from their fascia.
It was only after that process was complete that we thought to do one of the things we should have done up front — test the range of motion. We put the necks into poses of maximal extension, flexion and lateral deflection. Contrary to what I would have expected, the last of these was significantly more impressive than the other two, and is shown here. You can easily make out the separate extents of vertebrae 2, 3, 4 and 5, and from those see where 1, 6 and 7 are.
(Those are the long epaxial muscles in the background.)
We continued removing muscle and fascia until we had the vertebrae as close to naked as we could manage without risking damage to them, while retaining the integrity of the intervetebral joints — both intercentral and zygapophyseal articulations. One of the big surprises to us was how very flexible and fragile the latter were compared with the former. The membrane that contains the zygapophyseal joint is very thin and would contribute almost no mechanical strength of its own. By contrast, the adjacent centra were bonded very firmly together by extremely tough tissue. There was no trace of a separate cartilage disc between any pair of centra, just this very dense but flexible material which had to be slowly cut away with scalpels before the vertebrae could be be separated.
The exception to this was the atlas-axis joint, which surprised all three of us in how completely different it was to all the others. There was no connective tissue at all between the front of the axis and the back of the atlas — the two bones (or rather their cartilaginous surfaces) were free to move against each other without let or hindrance, as shown here (right anterolateral view with anterior towards the bottom of the picture):
And yet the axis was very firmly attached to the axis: although we couldn’t see any attachment, it wouldn’t come away — not even when a great deal of force was applied. The connection turned out to be between the ventral face of the odontoid process and the dorsal surface of the ventral portion of the atlas. (If you’re not familiar with anterior cervicals, this should become clearer later on when I show you the individual bones.) Suffice it for now to say that the atlas is basically ring-shaped, and that the odontoid process is a chunk of the axis that sticks out the front of that bone and sits within the O of the atlas.
Before we separated the vertebrae, though, we prepared the nuchal ligament out from its surrounding muscle. Here it is, with John and Darren holding its posterior portion up above the vertebrae: you can see that it’s in the form of a sheet rather than, as often envisaged, a cylinder. (It does extend further anteriorly than shown here, but its much less extensive over C2 than it is more posteriorly.)
We did the best we could at detaching this ligament intact so that we could measure how compliant it is. It was difficult to remove without damaging, and much more irregular in shape than we’d expected, so that the anteriormost portion had almost no strength and broke as soon as we exerted any force on it.
We were initially able to remove a portion that measured 45 cm at rest (from a total neck length of 51 cm, remember), but once the thin anterior end had broken off, we were left with 32 cm. We were able, by application of a significant force courtesy of Darren, to extend this to 42 cm but no further. That’s a strain of (42-32)/32 = 0.3125, which is a lot less than I’d been expecting. Alexander (1989:64-65) wrote (in the passage that was my first ever encounter with nuchal ligaments):
I am going to suggest that these necks [i.e. those of sauropods] were supported in the same way as the necks of horses, cattle, and their relatives. These animals have a thick ligament called the ligamentum nuchae running along the backs of their necks (figure 5.5). Unlike most other ligaments it consists mainly of the protein elastin, which has properties very like rubber. It can be stretched to double its initial length without breaking […] In experiments with deer carcasses, my colleagues and I found that the ligament was 1.4 times its slack length when the head was raised to the position of figure 5.5 [i.e. a typical alert posture], and almost twice its slack length when it was lowered to the position of figure 5.5b [grazing posture]. Notice that the ligament was stretched even when the head was high: I doubt whether a deer can get into a position that allows the ligament to shorten to the point of going slack. If you cut the ligament in a dissection the cut ends spring apart, as if you had cut a stretched rubber band.
So the least stretched life position of the ligament, according to Alexander, is significantly more extended than the most stretching we could achieve. What does this mean? I see four possibilities:
- Alexander was talking a pile of poo. I don’t believe this for a moment, and mention it only for completeness.
- I am talking a pile of poo. I can see why you’d think so, but I know it ain’t so (and Darren and John can verify it).
- The composition of the nuchal ligament changes through ontogeny, becoming more elastic as the animal gets older: we had a baby, and Alexander had adults. I don’t think this is very likely either — I can’t see any reason why juveniles would need less elastic ligaments than adults.
- The composition of the giraffe nuchal ligament is different from that of the deer.
Since I already eliminated the first three options, it won’t come as a great surprise to find that I favour the last one. And this has some interesting implications if it’s true. (Darn, darn, we should have saved a chunk of the ligament and found a way to get it analysed for composition.) If that nuchal ligament of giraffes is largely collagen rather than elastin, then it suggests the possibility of something similar for sauropods, and that would be interesting because the tensile strength of collagen is much greater than that of elastin.
Does anyone know if anyone’s done any work on this?
Well, anyway.
I drew the long straw, and got to bring the remains of the neck home to prepare out as bones. I simmered gently, then removed the cooked flesh, and was astonished to find how much there was, removed from vertebrae that we thought we’d cleaned pretty well at dissection time:
The disappointing part of this is that such large parts of the vertebrae turned out to be cartilage (partially ossified, I guess) and so came away during the simmering: huge chunks at the front and back of each centrum, like a full centimeter at each end, and all of the zygapophyseal articular surfaces. I wish I could have kept them intact … and of course a different preparation method probably would have done. More stupid still, I neglected to get photos of the individual vertebrae before simmering, which would at least have enabled me to show you before-and-after comparisons. Sorry.
Anyway, having peeled off the soft-tissue including cartilage, I re-simmered, re-picked, then bathed in dilute hydrogen peroxide for two days, and dried out the vertebrae in the sun. This is the result — C1-C7 in order, in left lateral view:
Note that the odontoid process of the axis is a separate bone from the rest of the axis — you can see it on the left, between atlas and axis. There was a big chunk of sculpted cartilage joining it to the rest of the atlas, and that’s all gone now, so I am not sure how I am going to join it up — maybe layer on layer of PVA representing the cartilage?
Oh, and notice that the metal pin is still in C7.
In the picture about, I have laid the vertebrae out in such a way that the total neck length (front of C1 to C7) is 51 cm, the same as it was in life. Notice how this leaves huge gaps between the central: for example, as here between C5 and C6:
Needless to say, anyone trying to reconstruct the living animal from the bones alone — from fossils, say — would get a hopelessly wrong neck if they didn’t take the missing cartilage into effect. As we’ve noted before, the same is true of sauropod necks.
But just how informative is a juvenile neck? No doubt, the cartilaginous portions of these vertebrae were proportionally much larger than they would be in an adult, so we do need to be careful about casually extrapolating the huge gaps between ossified centra in the images above into our interpretation of sauropods. For sure, I now need to go through this process with the neck of an adult giraffe — and if anyone happens to acquire one, I would love the opportunity to dissect it, please contact me if this comes up!
But maybe it’s not quite so misleading as it looks — for two reasons. First, nearly all the sauropod specimens we have are from subadults, as shown by lack of fusion between scapula and coracoid in, for example, the Giraffatitan paralectotype HMN SII. So it may be that their vertebrae were also not fully ossified. And second, sauropods are more closely related to birds than to mammals, and in my limited experience bird necks seem to have a larger cartilaginous component than those of mammals.
Well. Draw your own conclusions. But keep ’em qualitative for now.
Next time, I’ll be presenting a tutorial on how to dissect a neck. But it will be based on what we should have done rather than what we actually did.
Ask A Biologist — yet another new paper
March 17, 2011
Since the publication of Brontomerus, which let’s remember was only a couple of weeks ago, Matt’s had the rather bad manners to post about another new paper of his — a review of prosauropod pneumaticity which might be uncharitably summarised as “Were prosauropods pneumatic? The fossils say yes”. As though that weren’t enough, he had the audacity to follow up with another post about an article he’s just had published in the Australian science magazine Cosmos.
Well, I’m striking back: it’s been an unusually productive period for SV-POW!sketeers, because I was a co-author on another paper that actually came out a few days before Brontomerus, but which we didn’t have time to talk about back then. The new paper is:
- Hone, David W. E., Michael P. Taylor, David Wynick, Paolo Viscardi and Neil Gostling. 2011. Running a question-and-answer website for science education: first hand experiences. Evolution: Education and Outreach, published online ahead of print. doi: 10.1007/s12052-011-0318-5 [PDF available]
And it it’s all about the Ask A Biologist web-site.
I’ve been involved in Ask A Biologist since its inception in 2006, yet I’ve not really written about it here, which is very remiss of me. I think it’s a fantastic resource, and the publication of a formal paper about our experiences running it seems like a good opportunity to fix that.
In concept, Ask a Biologist is very simple: people ask biology questions, and a biologist answers them. We have a pool of to 20 or 30 biologists with different specialisms (though admittedly with a bit of a bias towards vertebrate palaeontology), and any of them might pick up and answer any question — or respond to any previously posted answer, which sometimes leads to interesting discussions. An example is discussed in the paper:
The somewhat frivolous question “What’s the best way to stop Velociraptor attacks?” attracted six answers. The first noted the general principle that it’s best not to go near large, fierce animals in the first place; the second went on to suggest climbing a spiral staircase, because dromaeosaurids such as Velociraptor had stiff tails that would have made them unable to negotiate tight bends; subsequent answers pointed out that the orientation of dromaeosaur wrists would have made it difficult for them to open doors as depicted in the Jurassic Park movies, and that, “in life” Velociraptor was much smaller than depicted on screen. It’s not unusual for a pop-cultural question like this to lead into answers that turn on details of anatomy: this we feel, can engage a child’s attention far more readily than conventional teaching methods and takes them farther than they might expect from what may have been a tongue-in-cheek question.
[Raptor comic by Randall Munroe of xkcd]
Ask A Biologist was the brainchild of Dave Hone, who was also lead author on the new paper describing the site, outlining its history, and describing the advantages and disadvantages of the way it’s set up. Dave is to be congratulated for getting this up and running, pushing it through three incarnations from its humble beginnings as a special-purpose blog into its present rather slick version, and drumming up enough interest to have attracted more than half a million visitors, with answers to well over 3,500 questions. As the paper points out, this has been done almost entirely on the basis of voluntary labour, for a very modest total cost of £3,750. In terms of cost-effectiveness, this is spectacularly successful science evangelism.
But the main reason Ask A Biologist is exciting to me is because it’s a manifestation of the Shiny Digital Future. As recently as a decade ago, there was a clear separation between working scientists and the rest of the world. Science happened over in a dark corner, and occasionally a scientist would deign to send a package of information out to the rest of the world. That’s changing, fast, thanks largely to the ubiquity of the Internet. Blogs such as Tetrapod Zoology, The Open Source Paleontologist, and indeed SV-POW! have played their small parts in this process — not only providing a means for researchers to describe what they’re doing, but enabling anyone who’s interested to engage with the scientists. But sites like Ask A Biologist are arguably even more significant, because they provide such an easy route for non-specialists to be in contact with experts. By design, most of the questions are asked by schoolchildren: they may be phrased with any level of sophistication, and we make an effort to couch answers accordingly. It’s a privilege to be involved in something that has such a catholic audience.
So how can you get involved?
By all means, read the paper, which describes Ask A Biologist in more detail than I can here. But there are two more important things you can do.
- Help to let the world know about Ask a Biologist. If you’re involved in a school (do you have children who attend one?) make sure that the teachers know about it. If you give talks at local natural history societies, leave the URL on a slide. (In a couple of weeks, I’ll be giving a talk about Brontomerus to the school that my eldest son attends: I’ll make sure to mention Ask A Biologist.)
- Those of you who are practicing scientists, please consider volunteering to be one of the experts who asks questions. If you’re interested, contact Dave Hone, who can set you up.
It’s a great project to be involved in!
Pneumaticity article in Cosmos
March 14, 2011
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.
Prosauropod pneumaticity strikes back
March 12, 2011
UPDATE April 16, 2012: The paper is officially published now. I’ve updated the citation and link below accordingly.
More new goodies:
This is only kinda sorta published. The accepted manuscript is now posted on the APP website, and it has a DOI, but it’s not formatted or available in print yet. But after discussing it amongst ourselves, we authors agreed that (1) the paper is globally available and it’s silly to pretend otherwise, (2) there are no nomenclatural ramifications of that fact, and (3) we’re tired of not being able to talk about this stuff. So we’re gonna, starting…now.
A brief tale of Serendipity in Science (TM):
Back in 2004 I was in my third year of grad school at Berkeley. My fellow grad student, Brian Kraatz, gave me a heads up about the 19th International Congress of Zoology coming up in Beijing. Attendees could submit 500-word abstracts or 2000-word short papers. I didn’t plan on doing either one, until the night before they were due, when I changed my mind and wrote almost all of what would become this paper in a single six-hour session (don’t be too impressed; I’ve been trying to replicate that feat for seven years with no success).
That summer, I met up with Brian in Beijing a week before the congress, and we spent the extra time working in the collections of the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP). Paul Barrett was there, working on prosauropods, and he and I had some long and fascinating conversations. We also gave our talks in the same session at the congress. Paul must have decided I was not a complete moron because he invited me to give a talk in the basal sauropodomorph symposium at SVP in 2005.
A brief aside: many of the animals I grew up calling prosauropods ended up outside of the monophyletic Prosauropoda that is anchored on Plateosaurus. Some are now basal sauropods, some are closer to sauropods than to Plateosaurus but outside of Sauropoda, and some are outside of Prosauropoda + Sauropoda. The phylogenetically correct term encompassing all of the nonsauropods is ‘basal sauropodomorphs’, and it means roughly what ‘prosauropods’ did until a decade or so ago. I often slip into informally using ‘prosauropods’, but I try to remember to put the term in quotes so as not to mislead anyone.
I had been to England in 2004 and 2005 and seen the putatively pneumatic vertebrae of Erythrosuchus and what was then known as Thecodontosaurus caducus (and is currently trading under the name Pantydraco caducus for reasons that it would be otiose, for the moment, to rehearse)–and, not incidentally, had finally met Mike in person, although we’d been corresponding since 2000. I’d also been to Stuttgart primarily to see the appendicular material of Janenschia and ended up spending some quality time with Plateosaurus. (Since the theme here is serendipity, note that the Janenschia work–my raison d’etre for going to Germany–died on the table, whereas I’ve now been an author on three ‘prosauropod’ papers and have more in the works. Weird!)
Anyway, with all of that accidental experience with ‘prosauropods’ and other interesting critters like Erythrosuchus, I found that I actually had something to say in 2005 SVP symposium. I titled my talk, ‘What pneumaticity tells us about “prosauropods”, and vice versa’, and it turned into the 2007 paper of the same title.
None of this would have happened if Brian hadn’t hounded me about going to Beijing, and if I hadn’t ended up talking so much with Paul on that trip, and if I hadn’t finished up with Janenschia on my first day in Stuttgart and spent the rest of the week playing with Plateosaurus. And so on. Science is unpredictable, especially for scientists.
When I sent around the PDF of the paper to friends and colleagues, I included this quip: “Were prosauropods pneumatic? The fossils don’t say. Somehow I stretched that out to 16 pages.” Mike claims that because of this quip he’s never been able to take that paper seriously. But it is my favorite among my solo efforts. It includes loads of stuff on the origins of air sacs and pneumaticity that I wasn’t able to get into my earlier papers, either because it wasn’t directly relevant or because some reviewer forced me to excise it.
BUT.
Almost immediately after the paper came out, Adam Yates and Matt Bonnan went and found roughly a zillion pneumatic ‘prosauropods’, which was a bit embarrassing since I’d just concluded that the evidence for ‘prosauropod’ pneumaticity was thin to nonexistent. So it is a damn good thing for me that I was already on friendly terms with both of them, because instead of taking the opportunity to smack me down, they invited me on board. Which led to Adam’s talk at SVP in Bristol in 2009, and to the new paper.
And actually, the depth of my incorrectness was even greater than I had thought. I reckon that literally millions of people have seen the mounted Plateosaurus skeleton in the AMNH, and any of them who have looked closely have seen this:
(Click for full size, unlabeled version.)
You see the problem here, I’m sure: the semi-big, semi-obvious fossa divided by an accessory lamina, not consistent with a muscle attachment point or fat pad or cartilage or infection, but very consistent in both form and location with the pneumatic fossae of other, more derived sauropodomorphs. On the lateral face of the vertebra, probably seen by millions, obvious to anyone who cares to look. A pneumatic prosauropod, in other words, right out in public for decades and decades (this time I don’t have to use the scare quotes because Plateosaurus actually IS a prosauropod sensu stricto). I didn’t even notice the first time I visited the AMNH back in 2006. I took the above photos, which are the basis for Figure 4 in the paper, in 2009.
So: ‘prosauropods’ were pneumatic. Some of them. A little bit. If you’d like to know more, please read the paper–it’s free.
Finally, a big thank-you to Adam and Matt for inviting me to be part of this. I think it’s pretty cool stuff, and I’m sure I’ll have more to say about it in the future. They might too–you should be reading their blogs, Dracovenator and Jurassic Journeys, anyway.
We’re still not done with Brontomerus, by the way. If nothing else, there’s the long-overdue post on how sauropod ilia change (or rather fail to change) through ontogeny. But that’s something we’ll have to get back to next week. Stay tuned.
Needless to say, one of the things I love most about Paco’s Brontomerus artwork is that it’s a rare and welcome example of the much neglected Sauropods Stomping Theropods school of palaeo-art.
When I reviewed the examples I know of, I was a bit disappointed to find that they number only five. Here they are, in chronological order.
First, we have this gorgeous sketch by Mark Hallett, showing Jobaria (here credited as “unnamed camarasaurid”) quite literally stomping on Afrovenator:
To the best of my knowledge, this has never actually been published — I found it on Dave Hone’s Archosaur Musings, in the interview with Hallett. Mark tells me that this was a concept sketch of possible main art for Paul Sereno’s North African dinosaur article, Africa’s Dinosaur Castaways in the June 1996 issue of National Geographic (Sereno 1996) — three years before Jobaria was described[1] (Sereno et al. 1999); but for some inexplicable reason, it wasn’t used.
It seems incredible to think that there was no published, or even completed but unpublished, sauropod-stomping-theropod art before the mid-1990s, but I’ve not yet found any. I thought that Bakker might have come up with something in The Dinosaur Heresies (Bakker 1986) or The Bite of the Bronto (Bakker 1994); but I flipped through both and I don’t see anything relevant. Anyone know of anything earlier?
The next entry on my list is Luis Rey’s striking Astrodon, carrying away a raptor that bit off more than it could chew.
This appeared in Tom Holtz’s outstanding encyclopedia (Holtz 2007), which I highly recommend for every interested layman, including but not limited to bright kids. The image also turned up, with Luis’s permission, in the publicity for Xenoposeidon — notably in The Sun, one of Britain’s most downmarket, lowest-common-denominator tabloids, where it was a pleasant surprise indeed.
I just love the expression on the raptor’s face. He’s going HOLY CRAP!, and his buddies are all like, Hey, dude, c’mon, we were only playing! But Astrodon‘s all, Nuh-uh, you started this, I’m going to finish it.
Next up, and a year, later, we have this moody just-going-about-my-business Camamasaurus, squishing theropod eggs, nests and babies in a casual sort of way, as though he’s saying “Well, you should have got out of my way”:
As it happens, this one was done for me, by Mark Witton. It was intended as an illustration for a “Fossils Explained” article that I was going to do for Geology Today on the subject of (get ready for a big surprise): sauropods. In fact, I am still going to do it. But since it’s been two and a bit years since I got the go-ahead from the editor, I’m hardly in a position to complain that Mark gave the image to Dave Martill and Darren when they suddenly needed artwork to publicise the findings of their Moroccan expedition. (Since then, the Mail seems to have re-used this picture pretty much every time they have a story about dinosaurs — even when that story is complete and utter crap.)
I don’t mind too much about this Witton original being whisked away from me, because shortly afterwards Mark went on to provide me with a much better piece — the beautifully wistful Diplodocus herd scene that we used in the publicity for our neck-posture paper.
And, amazingly, that brings us up to date. The next relevant artwork that I know of was Paco’s glorious Brontomerus life restoration, which you’ve already read all about. Just to vary things a bit, this is the second of the two renders — the one that wasn’t in the paper itself:
So is that the end of the story for now? Happily, not quite. Emily Willoughby produced this alternative Brontomerus restoration on the very day the paper came out!
I’m not going to claim that this is close to the quality of the other four pieces in this article, but you have to admire the speed of the work. Emily wrote most of the initial Wikipedia entry for Brontomerus, and produced this picture to illustrate it. At first when I saw this, I thought Emily had misunderstood the paper as indicating powerful retractors, so that the drawing had Brontomerus kicking backwards like a horse. But when I looked closely I realised it’s kicking outwards, thanks to the enlarged abductors. Neat.
A question and a challenge
I’d like to end this post with a question and a challenge. First, the question: what other pieces of palaeoart have I missed that feature sauropods handing theropods their arses? There have to be others — right?
And the challenge: I’d love it if those of you who are artists were to fix this terrible hole in the fabric of reality? I’d love to see new and awesome art on the timeless theme of sauropods stomping theropods. How about it? If any of you have influence with the Art Evolved people, you might try seeing whether you can get them to join in the challenge. It would be awesome to see a whole new crop of these pieces!
References
- Bakker, Robert T. 1986. The Dinosaur Heresies: New Theories Unlocking The Mystery of the Dinosaurs and Their Extinction. Morrow, New York. 481 pages.
- Bakker, Robert T. 1994. The Bite of the Bronto. Earth 3 (6): 26-35.
- Holtz, Thomas R., Jr., and Luis V. Rey. 2007. Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages. Random House, New York. 432 pages.
- Sereno, Paul C. 1996. Africa’s dinosaur castaways. National Geographic 189(6):106-119.
- Sereno, Paul C., Allison L. Beck, Didier. B. Dutheil, Hans C. E. Larsson, Gabrielle. H. Lyon, Bourahima Moussa, Rudyard W. Sadleir, Christian A. Sidor, David J. Varricchio, Gregory P. Wilson and Jeffrey A. Wilson. 1999. Cretaceous Sauropods from the Sahara and the Uneven Rate of Skeletal Evolution Among Dinosaurs. Science 282:1342-1347.
Footnotes
[1] If you want to call it that.
Friday follies: Raiders of the lost scap
March 4, 2011
Still, good or not, this does illustrate the danger of letting projects drag on forever.
Anyone else have horror stories of completely forgetting about work you’d done? The comment field is open.
Genesis of an instant palaeo-art classic
March 3, 2011
After a couple of relatively hardcore posts on ilial osteology, we though it would be good to look at something lighter this time. If you’re interested in dinosaurs, or indeed alive, you will hardly have been able to avoid seeing Francisco Gascó’s glorious life restoration of Brontomerus. Here it is again, in case you’ve been in a coma:
As well as being Figure 12 of the paper (Taylor et al. 2011), it’s popped up absolutely everywhere in media coverage: among many others, it was used by the BBC, Guardian, Telegraph and Independent in the UK; by USA Today, Fox News and National Geographic in the USA; by Spiegel in Germany; and by SVT (the state-funded national TV station) in Sweden. There’s no question that this image contributed hugely to selling the paper to the secular media. It’s probably responsible for 80% of all the coverage our work got, and I’m confident that it’s going to quickly become one of those images that everyone recognises, like the tyrannosaur/styracosaur fight on the cover of The Dinosaur Heresies and indeed Charles Knight’s classic swamp-bound Brontosaurus.
So it was a huge win for us, and it’s worth looking at how it came about.
Back in 2004, Matt gave a talk at the SVP annual meeting, entitled Skeletal pneumaticity in saurischian dinosaurs and its implications for mass estimates. The material in this talk became a chapter in the Wilson and Curry Rogers edited volume of sauropod papers (Wedel 2005). Some time in 2006, Matt heard about the Paleonturology competition, which is all about making palaeontology accessible for teenagers, especially in Spain: anyone who’d had a paper published in 2005 was invited to submit it, and the judges would choose the one that seemed most amenable to being rewritten in a compelling way for non-specialists. Matt’s 2005 paper won the 2006 competition, and the rewritten version of that paper was translated into Spanish and published in a very nice booklet which I am pleased to have a copy of (Wedel 2007). In 2007, Matt was invited to the Fundación Dinópolis in Teruel, Spain, to receive his award, launch the booklet, and act as a judge for the 2007 competition.
The relevance of all this now finally becomes apparent: while in Teruel, Matt met Francisco “Paco” Gascó, and looked through some of his portfolio of palaeo-art — including, for example, this rearing Camarasaurus:
So Matt had Paco in mind as a promising palaeo-artist. Then towards the end of May 2008, when we were readying the Brontomerus paper for submission (not to Acta Palaontologica Polonica — to a different journal, which didn’t take it) I wrote to Matt saying:
I’m attaching a tentative skeletal reconstruction that I did. […] Now I’m thinking: should we approach a palaeoartist to see if we can get a life restoration done in time for the launch? The eponymous thunder thighs hardly make an impact in the skeleton, after all.
And Matt quickly replied suggesting that Paco could be the person to do it. He sent a few samples, including the Camarasaurus above, and I was sold. A couple of days later, Matt suggested the idea to Paco, he was up for it, and so we were all systems go.
At that time, Paco (who is now getting towards the back end of his Ph.D) was a humble recent graduate, which was great because it meant that Matt and I got to boss him about — something that he accepted with enormous good grace as we went through a sequence of some 44 images on the way to the pair that we ended up with.
By this time, Matt and I had already realised that we wanted the artwork to show kicking. So we started out by asking Paco to mock up three very rough sketches of how he thought a Brontomerus-kicking-a-predator scene might be composed. Here is one of the three — pretty representative:
Although this scenario is pretty sweet, it’s not really what we wanted as it shows Brontomerus kicking backwards like a horse, rather than forwards like a footballer. (That’s a soccer player, for those of you in the USA.) So Matt offered this concept sketch:
(It’s well worth clicking through and seeing the details.)
It’s interesting to see how much of the final image was already in place even in that very early sketch: the basic pose of the adult sauropod, the juvenile behind, the theropod getting its arse kicked — even if at this stage it was a juvenile Acrocanthosaurus rather than a mature Utahraptor.
With this reference in the back of his mind, Paco started work on a 3D model of the sauropod that would be the core of the composition. He was quickly able to show us a first draft that had all the pieces in place to look convincing at least as a generalised sauropod:
Already at this stage, I was pushing for the uniquely Brontomerus-like aspects of the anatomy to be made more apparent, so I sent back this modified and uglified version of the image to give a sense of where we wanted to be heading:
(You might want to open this image and the previous one in two tabs and switch back and forth between them.)
The purpose of the modified version, of course, was to show how high the ilium would sit on the torso and how it brings forward the anterior margin of the leg muscles. We wanted the thigh to be much more thundrous! This was part of a merciless campaign of anatomical criticism of many, many aspects of the in-progress restoration — for example, the cross-sectional shape of the neck, which at this point had a crest on top and flat sides. (You’ll notice that in the final version, the neck has the distinctive subtriangular cross-section that is produced by the ventrolateral excursion of the cervical ribs in sauropods.)
While that stream of refinement was going on, Paca was starting to skin the model. Here’s the first version we saw that had skin texture:
Seeing this was an exciting moment in the progress of the project. It was the first time that the artwork started to look like actual art, and the sauropod to look like an actual sauropod. We knew then that we were on the way to somewhere good.
That feeling intensified the first time Paco showed us the complete cast of our little drama: mother, baby, and evil raptor, all skinned and showing rather fetching stripes which survived in more or less this form through to the final version:
By this stage, most of the anatomical problems are getting ironed out: the flat-sided shape of the neck has gone, replaced by a broader and wrinklier ventral aspect; and the ilium was higher on the torso, with the shape of the dorsal margin more closely reflecting that of the Brontomerus holotype ilium.
Note the care that Paco took with the juvenile: it’s not just a scaled-down copy of the adult, but proportioned subtly differently in a way that reflects what we know of sauropod ontogeny: the limbs grow isometrically, but the neck is positively allometric, so that Baby Bronto’s neck is noticably shorter in proportion. At this stage, the baby is too big — more than half Mama’s size, whereas the sizes of the elements from the Hotel Mesa quarry suggested that he should be closer to a third of her size.
At the same time that Paco was working on the details of the models, we were all still batting around composition ideas, trying to find the best way to put our three actors together. This version of Paco’s was similar in concept to Matt’s earlier sketch, but different in a lot of details: the baby is running away rather than sheltering, the theropod is rather bigger than before, and has morphed from an acrocanthosaur to a raptor; and it’s upside-down in an attempt to show that it’s not in control of the situation:
I wasn’t convinced by this version, because the theropod seems to have been spun 180 degrees on the spot as well as kicked upside-down: I felt that he needed to be in a posture that more naturally emerges from having been facing Mama when he was kicked, so I ‘shopped Paco’s sketch into this version:
As well as turning the baby around (something that didn’t really help). I flipped the raptor and tried, clumsily, to convey that Mama had broken its neck. Of course, that didn’t really work, because the extension at the base of the neck is habitual for most tetrapods anyway, but it at least gave us a sense of the direction we wanted to go in.
OK, so back to the model. Paco had sent us a simple lateral-view render of Mama alone, as well as the group shown above, so that we could more easily critique its anatomy in isolation. Here is that simple render, followed by the vandalism I did on it to show changes that we still wanted. (See what I mean about Paco being patient?)
As you can see (and as you’ll see more clearly if you flip back and forth between the two images), I was asking for two changes. The simpler was that I wanted to see the distinctive profile of the Brontomerus scapula showing through the skin. The more interesting is in the profile of the tail. It’s been shown in many sauropods that there is a distinctive upwards kink at the base of the tail, so that the dorsal profile of the body does not progress smoothly from hips to tail, and I wanted to see that in Brontomerus. At the same time, the tail needed to have more flesh on it and the ischium should have been producing a visible bulge in the ventral margin behind the hips.
The next version addressed these points (though the scapula outline was not yet right):
But picky as I am I still wasn’t satisfied…
I made a few changes here — again, in a hacky way using the GIMP, with the result not in any way intended as in improvement in itself, but as a sketch of how the model could be improved. I shifted the tail up a little, smoothed the dorsal profile so that there was no longer a sort of dip at the base of the tail, and smoothed out the rear margin of the top of the thigh, so that there was no longer a “buttock”, but a hint of caudofemoralis musculature connecting the tail-base with the thigh.
Once Paco had made the necessary changes to the model, the next render looked superb — and very recognisable as the basis of the now-ubiquitous final version:
At this point, work on the main model was essentially complete, and Matt and I were both really happy with the result. For people who’ve spent as much time gazing at the Brontomerus ilium and scapula as we have, this is very obviously Brontomerus and not just a generic sauropod. Now it was time to put the model together with the composition ideas we’d been playing with:
We went through several versions of this, mostly varying in the posture of the theropod, but this is the one that led to the final piece. For the first time, we were all happy with Baby Bronto in this one, too: he’s about the right size, and has a sort of skittering look to him, as though he wants to be elsewhere but doesn’t want to leave Mama. (Am I anthopomorphising? Very well; I contain multitudes.) It’s a bit too close to the adult, though, so we can’t quite see its shape. This was fixed in the next version, which also contained a backdrop for the first time:
Now we’re really getting somewhere. You’ll notice that the raptor’s head is bent further back this time, hopefully conveying that its neck is broken. But because I was really keen on getting it across that the raptor is DOWN and it’s NOT getting up again, I once again vandalised Paco’s work, this time with buckets of blood:
What I wanted to convey was: if this raptor wasn’t already secondarily flightless, it is now. Still, I admit that the amount of blood, and the vividness of its colour, are a little over the top. So in the final version, Paco took some of the blood back out, and toned it down to a more realistic colour. The other important difference is that the raptor was moved a bit closer to the sauropod — not because that’s necessarily a better composition, but because we expected newspapers and other media outlets to crop the image mercilessly, and we wanted to give them best chance of keeping all the key element in frame when they did.
And so we arrive at the final version, as it appeared in the paper:
The very last thing we did was ask Paco for a second render of the same scene, so that media outlets would have a choice of artwork and wouldn’t all need to use the exact same image. That was doable because all three dinosaurs, with their skin-textures, were built as a 3D model, which can be viewed from any angle. But producing a finished artwork from this is not trivial: once an angle is chosen and the animals rendered, there is still a lot of post-production work to be done in putting in the background, the blood, the dust and so on. So we didn’t ask for a complete array of 128 of these — just the one addition. After reviewing a few candidate exported renders, we settled on one from a more anterolateral perspective, and Paco worked his magic to yield this alternative take:
I hardly have words to tell you how much I love this. Several times, looking at it, I’ve found myself laughing out loud at how comprehensively the theropod is getting owned. It’s OVER for that would-be predator. It’s DONE. The only question is whether Mama is going to put it out of its misery by stomping it flat, or whether it’ll be left to bleed out. Either way, it picked on the wrong victim for dinner.
Part of what I love so much about this is that Brontomerus looks like an animal, not like a monster. It works anatomically, feels like something that lives and breathes … and, indeed, kicks.
Let me close by clearly stating that 99% of all the Awesome here is the work of Paco — a talented and hardworking guy, who made Matt’s vision come to life. My own input was basically restricted to whining. I hope we’ll be seeing this image for many years to come, and that plenty more of Paco’s pieces make it out into the wide world where they belong.
For more of Paco’s stuff, please see his blog, El Pakozoico (TARDIS alert!), and his deviantART page.
References
- Taylor, Michael P., Mathew J. Wedel and Richard L. Cifelli. 2011. A new sauropod dinosaur from the Lower Cretaceous Cedar Mountain Formation, Utah, USA. Acta Palaeontologica Polonica 56(1):75-98. doi: 10.4202/app.2010.0073
- Wedel, M.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.
- Wedel, M.J. 2007b. Aligerando a los gigantes (Lightening the giants). ¡Fundamental! 12:1-84. [in Spanish, with English translation]
Reconstructing the ilium of Brontomerus
March 1, 2011
Let’s look a bit more closely at the holotype element of Brontomerus mcintoshi, which as we all remember is the juvenile left ilium OMNH 66430. Much of what we’ve said about Brontomerus is based on the shape of that ilium, so it’s important to get right. Several commentators have expressed skepticism about how we reconstructed, so I thought it would be worth taking the time to explain why we put it together we way we did.
First, let’s orient ourselves. Here is the torso from the skeletal inventory that was Figure 1 of the paper (Taylor et al. 2011, natch). In this version, I’ve highlighted the ilium in red. We’re looking at the left side of the animal, so the main part of the bone is further forward than the hip socket, towards the animal’s head.
As you’ll see from the area that we left shaded grey, a chunk is missing from the middle of the ilium, where it was damaged in the field. As the figure of the ilium in the paper shows clearly, what we actually saw in the OMNH collection was three chunks of bone: a big one consisting of the acetacular margin, pubic and ischiadic peduncles and most of the preacetabular blade; and two smaller fragments, each contributing part of the dorsal or posterior margin.
We spent a while in the OMNH collection playing with the three chunks to see how they best fit together. In doing this with the actual bones, we were able to take account of their curvature in the third dimension, which our figure don’t show — although a dorsal-view photo gives some idea.
Anyway, we this is what we came up with:
(Sorry if that image is getting a bit overfamiliar, but it’s worth seeing again in the context of this post.)
You’ll remember from the Clearing the Air post that Jim Kirkland, who excavated the ilium, felt that we’d got the two smaller fragments in the wrong places relative to the main chunk, and also that a fourth fragment which we’d missed also belongs to the ilium. He kindly sent a photo of how he’d reconstructed the ilium, and I used the arrangement of pieces in the photo as the basis for a “what if” alternative reconstruction.
So far, this is old news. But what was maybe not quite clear in the post is how very similar the two reconstructions really are. Let’s fix that: here they are side by side, with ours on the left and Jim’s on the right:
It seems pretty clear that even if Jim’s arrangement is correct (which Rich Cifelli disputes), that doesn’t affect the reconstruction in any significant way.
But the real question is why we put in that dotted line — and why we put it where we did. How do we know there wasn’t a normal-sized postacetabular lobe sticking out behind? This is what Jamie Headden wanted to know in an email to me shortly after the paper come out. With his kind permission, I reproduce the illustration that he prepared, showing (A) the reconstruction from the paper, and (B) how it might have been different:
The reason we rejected a reconstruction like the one in Jaime’s part B is explained (too) briefly in the paper (pp. 80-81):
The postacetabular lobe is reduced almost to the point of absence […] The ischiadic peduncle is reduced to a very low ventral projection from almost the most posterior point of the ilium. The near absence of the ischiadic peduncle cannot be attributed to damage as the iliac articular surface is preserved. Immediately posterodorsal to this surface is a subtle notch between the peduncle and the very reduced postacetabular lobe. This notch and the areas either side of it are composed of finished bone, demonstrating that the great reduction of the postacetabular lobe, too, is a genuine osteological feature and not due to damage.
To my lasting annoyance, I didn’t take any posterior-view photos of the ilium back in 2007, so I can’t show you this finished bone as well as I’d like — this was back before I’d learned all my lessons on how to photograph bones. But here is a close-up of the posterovental extremity of the ilium, again from Fig. 2, showing the notch: I have left the postacetacular lobe in colour, and desaturated the ischiadic peduncle — the notch is between them.
This next photograph of the ilium, again in lateral view, is lit rather differently from the one we used in the figure, so that you can see a distinct shadow lying along the valley between the ischiadic peduncle and what there is of the postacetabular blade.
Here’s one that shows the main chunk of the ilium in anteromedial view: from here, you can more easily see the the distinction between the ischial peduncle (which projects towards the camera) and the preserved, ventralmost, part of postacetacular blade, which is further back.
And one in posteroventral view: this is similar to our Fig. 2b, but from a slightly more posterior (and medial) perspective, so that you can more easily see the mediolaterally compressed posterior lobe sticking out behind the broader ischial peduncle at top right:
What all these photos unfortunately do not show is the finished nature of the bone on the posterior margin of the postacetacular blade — on that, you just have to take our word.
But the point is this: we have the whole of the ischiadic peduncle and the ventralmost part of the postacetacular blade — we know that the posteriormost preserved part of the main chunk of ilium is not part of the peduncle (so that the postacetabular blade is missing), but that this really is the blade itself. And because the bone is not broken, we know that the trajectory of the posterior margin of the postacetabular blade was directed dorsally from the posterior point of the peduncle.
I hope that’s clear. What I really should have done, of course, was take my own good advice and get photos from every angle — and, ideally, pairs that would have allowed me to show the relevant features as anaglyphs.
Anyway, all this shows that the shape of the ilium really was pretty much as we reconstructed it — and, most, importantly, that the bizarre proportions we reported in Table 4 are correct: preacetabular blade, measured parallel to the longest axis of the ilium equal to 55% of total length; postacetabular blade equal to 0%.
Exactly how strange is this almost non-existent postacetabular blade? In the paper we described it as “remarkable”, but it’s not completely unprecedented. Lehman and Coulson (2002:fig. 8) showed the left ilia of six somphospondylians:
As you can see, the Euhelopus zdanskyi and Saltasaurus loricatus ilia both lack postacetabular blades (although Powell 1992:fig. 18 suggests that the posterior portion of the Saltasaurus ilium may be broken). Where Brontomerus is unique is in the combination of this postacetabular reduction with the enormous preacetabular blade.
All clear? Good.
…
“But wait!”, I hear you cry. “That ilium is juvenile! How do you know that its strange shape is not a juvenile feature?”
Stay tuned! All will be revealed.
References
- Lehman, Thomas M. and Alan B. Coulson. 2002. A juvenile specimen of the sauropod dinosaur Alamosaurus sanjuanensis from the Upper Cretaceous of Big Bend National Park, Texas. Journal of Paleontology 76(1):156-172.
- Powell, Jaime E. 1992. Osteología de Saltasaurus loricatus (Sauropoda-Titanosauridae) del Cretácico Superior del Noroeste Argentino. pp. 165-230 in: J. L. Sanz and A. D. Buscalioni (eds), Los Dinosaurios y su Entorno Biotico. Actas del Segundo Curso de Paleontologia en Cuenca. Instituto Juan de Valdés, Ayuntamiento de Cuenca. 397 pages.
- Taylor, Michael P., Mathew J. Wedel and Richard L. Cifelli. 2011. A new sauropod dinosaur from the Lower Cretaceous Cedar Mountain Formation, Utah, USA. Acta Palaeontologica Polonica 56(1):75-98. doi: 10.4202/app.2010.0073