June 25, 2009
This is corn on the cob:
This is a shish kebab:
Most tetrapods are like shish kebabs: a whole lot of meat stuck on a proportionally tiny skeleton. If you don’t believe me, you can look at the human and cow neck torso cross-sections in Matt’s last post, or check out this ostrich-neck cross-section from his 2003 Paleobiology paper:
Remember that this is a freakin’ ostrich — of all extant animals, one of the ones with a most extreme long, skinny neck. And yet, if sauropods were muscled like ostriches, then their necks would have looked like this in cross section:
And soft-tissue reconstructions would have to look like this:
Which, happily, no-one is suggesting. Instead, published reconstructions of sauropod neck soft-tissue are startlingly emaciated. As exhibit A, I call this pair of Greg Paul cross-sections:
(Yes, the Diplodocus on the left is the one I used in the photoshopped ostrich cross-section above. It’s instructive to compare Paul’s original with the What If It Was Like A Big Ostrich version.)
Paul’s reconstructions seem to be widely considered too lightly muscled. But even the very careful and rigorous more recent reconstructions of Daniela Schwarz and her colleague show a neck much, much thinner than that of the ostrich:
Although Schwarz has put a lot more soft tissue onto the neck vertebrae than Paul did, it is still a tiny proportion of what we see in extant animals — even the ostrich, remember, which has a super-thin neck compared with pretty much anything else alive today. If sauropod necks were muscled as heavily as those of, say, cows, then the soft tissue would pretty much reach down to the ground. But they weren’t: they were more like corn on the cob, with a broad core of skeleton and relatively little in the way of delicious edibles festooned about it.
So why is this? Why does everyone agree that sauropod necks were much less heavily muscled than those of any extant animal?
It’s a simple matter of scaling. A really big ostrich might have a neck 1 m long. (Actually, ostriches don’t get that big, but let’s pretend they do because it makes the maths easier). If the x meter-long neck of a sauropod was just a scaled-up ostrich neck, then it would be x times longer, x times taller and x times wider, for a total of x^3 times as voluminous and therefore x^3 times as heavy. But the cross-sectional area of the tension members that support it is only x times taller and x times wider, for a total of x^2 times the strength. In total, then, the neck’s mass/strength is x^3/x^2 = x times as great as in the ostrich. (The sauropod neck’s mass also acts further out from the fulcrum by an additional factor of x, but that is cancelled by the fact that the tension in the neck also acts x times higher above the fulcrum.)
It seems intuitively obvious (which is is code for “I have no way to prove”) that you can’t reasonably expect the neck muscles of a giant ostrich to work ten times as hard as they do in their lesser cousins, which is what you’d need to do for the 10 m neck of, say, Sauroposeidon. So simple isometric scaling won’t get the job done, and you need to restructure the neck.
But how? Surely just reducing all the muscle around the vertebrae can’t help? No indeed — but that is not really what sauropods were doing. If you look at the typical sauropod-neck life restoration, you’ll see that the proportional thickness of the neck is actually not too dissimilar to that of an ostrich — rather thicker, in fact. If you scaled an ostrich neck up to sauropod size and compared it with a real sauropod neck, you would find not that the soft tissue was too fat, but that the vertebrae were too thin.
And so we come to it at last: rather than thinking of sauropods as having reduced the amount of soft-tissue hanging on the cervical vertebrae, we do better to think of them as having kept a roughly similar soft-tissue profile to that of an an ostrich, but enlarging the vertebrae within the soft-tissue envelope. Of course if you just blindly made the vertebrae taller and wider, they would become heavier in proportion, which would defeat the whole purpose of the exercise — but as everyone who reads this blog surely knows by now, sauropod cervicals were extensively lightened by pneumaticity. By bringing air into the center of the neck, they were effectively able to displace bone, muscle and ligament away from the centre, so that they acted with greater mechanical advantage: higher epaxial tension members, lower hypaxial compression members, and more laterally positioned paraxials.
It’s a rather brilliant system — using the same volume of bone to achieve greater strength by displacing it outwards and filling the center with air (and, in doing so, also displacing soft tissue outwards). And it will be hauntingly familiar to anyone who loves birds, because it is of course exactly what birds (and pterosaurus) have done in their long bones: the hollow humeri of flying vertebrates famously allow them to attain greater strength — specifically, resistance to bending — for the same volume and mass of bone. It’s a neat trick when done with long bones, but it takes a truly awesome taxon to do it with the neck.
So maybe sauropods were not corn on the cob after all. Maybe they were Hostess Twinkies.
Now that I’ve finished my Ph.D at the University of Portsmouth, what am I going to do with the rest of my scientific life? I’ve always said that I have no intention of going into palaeo full time: my knowledge is far too narrow for that, so that even if paid jobs were not in insanely short supply, I wouldn’t stand much chance of getting one. And in any case, I’d hate to get into the all-too-common situation of being up against a friend for a position we both wanted. Throw in the fact that I really enjoy my computer-programming day-job and it seems pretty clear that what I need is an unpaid affiliation that lets me get on with lovely research.
Well: I am absolutely delighted to announce that, as of last month, I am an Honorary Research Associate in the Department of Earth Sciences at UCL. It’s not just that UCL is such a well-respected institution — see that Wikipedia article for some details — more importantly, it’s where Paul Upchurch hangs out, as Senior Lecturer in Palaeobiology. Sauropod fans will be familiar with Paul’s characteristically detailed and careful work, from his pioneering work on sauropod phylogeny (Upchurch 1995, 1998), through his and John Martin’s indispensible Cetiosaurus makeovers (Upchurch and Martin 2002, 2003) to the state-of-the art review that he lead-authored for Dinosauria II (Upchurch et al. 2004) and the Tokyo Apatosaurus monograph (Upchurch et al. 2005). What many of you won’t know is what an excellent collaborator he is — quick, conscientious, insightful and diplomatic. We’ve already collaborated on a few short papers (Upchurch et al. 2009 and a couple of Phylocode companion-volume chapters that are in press), and I hope there will be more in the future.
- Paul, Gregory S. 1997. Dinosaur models: the good, the bad, and using them to estimate the mass of dinosaurs. pp. 129-154 in: D. L. Wolberg, E. Stump, and G. D. Rosenberg (eds.), DinoFest International: Proceedings of a Symposium Sponsored by Arizona State University. Academy of Natural Sciences, Philadelphia.
- Paul, Gregory S. 1998. Terramegathermy and Cope’s Rule in the land of titans. Modern Geology 23: 179-217.
- Schwarz, Daniela, Eberhard Frey and Christian A. Meyer. 2007. Pneumaticity and soft-tissue reconstructions in the neck of diplodocid and dicraeosaurid sauropods. Acta Palaeontologica Polonica 52(1): 167-188.
- Upchurch, Paul. 1995. The evolutionary history of sauropod dinosaurs. Philosophical Transactions of the Royal Society of London Series B, 349: 365-390.
- Upchurch, Paul. 1998. The phylogenetic relationships of sauropod dinosaurs. Zoological Journal of the Linnean Society, 124: 43-103.
- Upchurch, Paul and John Martin. 2002. The Rutland Cetiosaurus: the anatomy and relationships of a Middle Jurassic British sauropod dinosaur. Palaeontology, 45(6): 1049-1074.
- Upchurch, Paul and John Martin. 2003. The anatomy and taxonomy of Cetiosaurus (Saurischia, Suaropoda) from the Middle Jurassic of England. Journal of Vertebrate Paleontology 23(1): 208-231.
- Upchurch, Paul, Paul M. Barrett and Peter Dodson. 2004. Sauropoda. pp. 259-322 in D. B. Weishampel, P. Dodson and H. Osmólska (eds.), The Dinosauria, 2nd edition. University of California Press, Berkeley and Los Angeles. 861 pp.
- Upchurch, Paul, Yukimitsu Tomida, and Paul M. Barrett. 2005. A new specimen of Apatosaurus ajax (Sauropoda: Diplodocidae) from the Morrison Formation (Upper Jurassic) of Wyoming, USA. National Science Museum Monographs No. 26. Tokyo. ISSN 1342-9574.
- Upchurch, Paul, John Martin, and Michael P. Taylor. 2009. Case 3472: Cetiosaurus Owen, 1841 (Dinosauria, Sauropoda): proposed conservation of usage by designation of Cetiosaurus oxoniensis Phillips, 1871 as the type species. Bulletin of Zoological Nomenclature 66(1): 51-55.
- Wedel, Mathew J. 2003. Vertebral pneumaticity, air sacs, and the physiology of sauropod dinosaurs. Paleobiology 29(2): 243-255.
June 22, 2009
This is a taco.
This is a corn dog.
Here’s a cross-section of a human. In the terms of fast food, people are corndogs. Most of us even have an outer ring of yellow adipose ‘breading’.
Here’s a cross-section of a cow. In an example of function following form, cows are, and often become, corndogs.
Note that in both the human and the cow the spaces between the neural spine and transverse processes are completely filled with back muscles, which in fact bulge out beyond the tips of the neural spine, as we also saw here. This despite the common paleoart convention of presenting dinosaurs as thin layers of skin conforming perfectly to the underlying skeleton. Just Say No to shrink-wrapped sauropods!
Here is Figure 17 from Holland (1910), one of the most badass scientific smackdowns ever published, in which Holland wiped the floor with Hay, Tornier, and the idea of sprawling sauropods. On the left are torso skeletons of three lizards and a croc; on the right is an anterior dorsal with articulated ribs from Diplodocus. As you can see, it’s a taco, and its taconic form would be perfected if it could roll supine.
The point of the post is not that sauropods had deep, slab-sided bodies. We’ve covered that before. The point is that sauropod torsos are seriously weird. In mammals, the dorsal ribs arch up and out, away from the vertebra, before sweeping around to define the anterior body wall. In lizards, the proximal part of each rib sticks out sideways. In sauropods, the ribs point down. This is mainly because the vertebrae are FREAKIN’ HUGE compared to the size of the body. Whereas in the mammals and lizards the dorsal vertebrae are titchy little things that span a small fraction of the width of the torso, in Diplodocus and other sauropods the dorsal vertebrae account for about half. (The cow cross-section missed the transverse processes, so that vert looks narrower than it actually is.)
This is relevant when we think about the function of pneumaticity. When I write that pneumaticity lightened vertebrae, I usually mean relative to that same vertebra if it wasn’t pneumatized. But we could also ask if the pneumatic vertebra is lighter than a vertebra from a similar-sized animal that lacks pneumaticity–except that, for big sauropods, there are no similar-sized terrestrial animals without pneumaticity to compare.
Imagine that in a big sauropod the dorsal vertebrae are three times as wide and three times as tall as they would be in a similar-sized mammal. They should weigh nine times more. But let’s also assume that the vertebrae of the sauropod are 85% air by volume, which is in fact pretty typical for Early Cretaceous brachiosaurids. The mass of the dorsal column relative to that of the mammal is then 9 x 0.15 = 1.35, a little heavier, but not much (I’m assuming the length of the torso is the same in the two animals). Bigger bones mean better lever arms for the muscles and lower bending stresses on the ribs, which can function more like curtains and less like cantilevered beams.
I can’t think of much published discussion of this stuff as it relates to sauropods, but it seems like it might be important.
Holland, W.J. 1910. A review of some recent criticisms of the restorations of sauropod dinosaurs existing in the museums of the United States, with special reference to that of Diplodocus carnegiei [sic] in the Carnegie Museum. American Naturalist 44:259-283.
June 16, 2009
Sorry to keep dumping all these off-topic thoughts on you all, but I got an email from Matt today in which he suggested that there should be some system of giving people credit for particularly insightful blog comments. (This came up for the obvious reason that SV-POW! readers tend to leave unusually brilliant comments, as well as having excellent reading taste and being remarkably good looking.) That led me into the following sequence of thoughts, which I thought were worth blogging — not least in the hope that we can learn something from the comments.
But first, here is that photo of another fused atlas-axis complex that you ordered (seriously, what’s up with these things?):
And now, on with the uninformed noodling:
As things stand at this point, we have a hierarchy of sciency documents. At the top (which we’ll call level 1) come papers. The reputation of papers is largely determined by formal pre-publication reviews (which we will therefore classify as level 2) — and, increasingly, also by blog posts about the paper, which are also level 2. Classic peer-reviews are only ever seen by the editor and the author of the original paper; once they have been absorbed into the paper they’re critiquing, they disappear forever, which is a crying shame. But the other kind of level-2 literature, the blog post, has a life of its own: and so it gets commented on by blog-comments (level 3). Each level gives validity to the level above.
More important, documents at each level also give validity to each other. The most important case is that when one paper favourably discusses another, or refers to its authority, it gives the latter a credibility boost (which is why it’s such a sod that no-one cites any of my papers); similarly, our SV-POW! posts also get a credibility boost when they’re discussed on Tetrapod Zoology or Blog Around the Clock (and I just repaid the compliment by linking back to them).
(At present, all of this is done in a messy qualitative way, with no numbers attached, except occasionally in the case of pre-publication reviews. That’s a shame: if, for example, blog commenters allocated the posts a score out of ten, then we could use some kind of average score as a quality filter: to ameliorate rigging, I’d suggest discarding the highest and lowest 10% of awarded scores, and averaging the remainder.)
Now the problem: blog comments are right at the bottom of the pile: who is going to rate them? I’m certainly not going to spend any time on that.
OK, so suppose we ignore the arbitrary allocation of levels: papers, reviews, blog posts and comments are all just considered as documents, and all can discuss each other. (Clearly reviews will necessarily discuss papers more often the papers discuss blog comments, but that is a convention added to the system I am about to describe, not a precondition for it.) Each document has a reputation, which we will quantify as a single real number. Documents start with some arbitrary small reputation — probably 0.0 or 1.0, and it probably doesn’t much matter what it is. When any document discusses, cites or links to another — whether it’s paper, a review, a blog post or a comment — that linkee’s reputation is boosted by some proportion: 10%, say, of the linker’s reputation. Now of course this change in linkee reputation causes a trickle-down change of 1% in the reputation of the documents that it links to; and 0.1% in the reputation of the documents they link to, and so on. Reputations will change frequently and irregularly, and will be near impossible to calculate accurately, but that’s fine — they should be easy to approximate, and that’s good enough.
In this way, we get a nice solid score that we can use to decide what’s worth reading and what isn’t — the cream will naturally rise to the top. Hiring committees can throw away impact factors, and instead just add up the reputation scores of their candidates’ publications (either in the strict sense of the word, or including blog posts, reviews and/or comments). By the way, one of the positive effects of this would be that people like Darren and Jerry Harris would get some reward from their sterling reviewing efforts.
Sounds awesome? Here’s something even more awesome: we already have that system, more or less. Yes indeed: the reputation propagation algorithm I described is, in general outline, the same thing that Google does in the algorithm that it calls PageRank(tm)(r)(lol)(ymmv). We can — and already do — use Google’s notion of reputation as a guide to finding what’s worth reading, and we can tell that in works well in practice because SV-POW! posts rank so highly :-)
So that’s it! We can all stop worrying, just Google for stuff we’re interested in, and read whatever pops up at the top of the list!
Are you convinced? I hope not, because this idea has at least three huge problems.
1. What counts? (Yes, that again.) Google-ranking works well for blog posts, because they are web pages, and Google can spider web pages. But that leaves out reviews, because they are typically not published at all, let alone as web pages. And it leaves out comments, because they are appended to the end of blog posts rather than being pages in own right, with their own PageRank. And, worst of all, it pretty much leaves out the papers themselves — because there is, in general, no one single web-page which is The Place a particular paper lives. For non-open papers that aren’t hosted on the author’s page or elsewhere, there is no page. In short, reviews are not published, comments are not whole pages and papers are not single pages, so none of them is properly page-rankable.
2. All links count as positive reputation — there are no negative citations. So a document that says “Taylor, Wedel and Naish 2009 was talking a lot of nonsense about sauropod neck posture” would still be a score in our favour, even though it meant the exact opposite. Of course, this is not a new problem: both PageRank and Impact Factors suffer from the same problem, but it doesn’t seem to be a killer for either of them. The only fix for this would be to invite authors (of papers, reviews, blogs and comments) to explicitly score some or all of the other documents they mention — and I doubt people are going to be keen to do that unless the mechanism can be made very non-intrusive.
3. And here’s the killer: we wouldn’t, or shouldn’t, want Google to do this, even if they could overcome problems #1 and #2. Google is a private corporation, and we don’t want to hand over reputation management to any private commercial venture with an obligation to shareholders rather than scientists, and with a proprietary secret algorithm. If you doubt me, consider Thompson’s ownership of the Impact Factor and see where that’s got us. No doubt when Eugene Garfield came up with the idea of the Impact Factor, he was pretty excited about how — at last! — we would have an objective, reliable way to evaluate science. But IF is not run by scientists, it’s run by a corporation. With hilarious results.
I have no idea what the conclusion to all this is. I didn’t have a clear idea where it was headed when I started writing it. But, much in the manner of Dirk Gently when employing his usual method of navigation, I may not have ended up where I intended to, but I’ve arrived somewhere interesting.
Your move: what have I failed to take into account?
I have a much less realised view of the digital future than Matt does, so I won’t be making a lot of predictions here. But I do have some questions to ask, and — predictably — some whining to do.
What counts, what doesn’t, and why?
Assuming you have made some science (e.g. a description of fossil, a palaeobiological hypothesis supported by evidence, a taxonomic revision), there are plenty of different ways you can present it to the world. I may have missed some, but here are the ones I’ve thought of, in roughly descending order of respectability/citability/prestige:
- Peer-reviewed paper/book chapter
- Unreviewed paper/book chapter
- Peer-reviewed electronic-only paper
- Published abstract (e.g. for SVP)
- Conference talk
- Conference poster
- Online supplementary information
- Blog post
- Blog comment
- Email to the DML (which is archived on the web)
- Personal email
- Chat over a beer
How many of these are Science? Where is the line? Is the line hard or fuzzy? Why is it OK to cite SVP abstracts but not so much SVPCA abstracts? And other such questions. I think a very good case can be made that dissertations — provided they are made available — are better sources than conference talks, posters and abstracts; and a pretty good case can be made that blog posts are (especially when webcitation’ed — see below). Both dissertations and (good) blog posts have the advantage over talks and posters that they have a permanent existence, and over abstracts the simple fact that they are substantial: a 200-word abtract cannot, by its very nature, say anything much.
Unfortunately, for nomenclatural purposes, the ICZN’s Article 8 currently says that only publications on paper count, period, which counts out dissertations. I say unfortunately because were it not for this rule, then at least part of Aetogate would never have happened: the ramifications of Bill Parker’s case would not have been so awful if the perfectly good description of Heliocanthus in his (2003) dissertation had been allowed priority over Lucas et al.’s (2006) rush-job which attached the name Rioarribasuchus to the same specimen. Happily, the ICZN is as we write this considering an amendment to recognise nomenclatural acts in electronic-only publications. There has already been some published discussion of the pros and cons of this amendment, and the Commission is actively soliciting further comments, so those of you with strong feelings should put them in writing and send them to the Executive Secretary. (I will certainly be doing so.)
We all know that blog entries are Not Sufficiently Published to be citable, at least in most journals; but are they Too Published to let you re-use the same material? When you submit to most journals, they ask you to formally state “this material has not previously been published” — is that true if we’ve blogged it? I am guessing different editors would answer that differently. For what it’s worth, we’ve been reasonably careful up till now not to blog anything that we’re planning to make into a paper — which is why we were so mysteriously silent on the obviously important topic of sauropod neck posture during the first 19 months of SV-POW!. We’ve not been 100% pure on this: for example, I have a paper on Brachiosaurus in press that mentions in passing the spinoparapophyseal laminae, absence of an infradiapophyseal laminae and perforate anterior centroparapophyseal laminae of the 8th dorsal vertebra of the Brachiosaurus brancai specimen HMN SII — the features that I have blogged here in detail, with illustrations that would certainly never have been given journal-space. Since the relevant passage in my paper accounted for half a manuscript page (of a total of 75 pages), I’m assuming no-one’s bothered about that. In a case like this, I guess the SV-POW! posts are best thought of as pre-emptive and unofficial online supplementary information.
Counts for what purpose?
We’ve already mentioned that dissertations, blog entries and suchlike don’t count for nomenclatural purposes. Whether they count in the sense of being citable in published works is up for debate right now (and again, see below on webcitation). It seems pretty clear that these forms of “grey publication” do count in establishing people’s reputations among their peers — dissertations are obviously important in this regard, and Darren’s ridiculously broad knowledge of tetrapods extant and extinct is near-universally recognised largely because of his blogging efforts (although you could argue — and Matt and I often have argued — that he might have been able to enhance his reputation even more if he’d taken some of that blogging time and invested it in formal publications). Conversely, it’s clear that blogs, however rigorous and scientific, count for squat when it comes to committees. The world of dinosaur palaeontology is probably just as aware of Matt’s series of Aerosteon response articles here on SV-POW! as it would be if he’d put those together into a paper that was published in PLoS ONE; but when his tenure committee comes to count up the impact factors of the journals he’s published in, those articles will count for nothing. One day that might change, but not while impact factors still exert their baleful influence.
Deciding what to blog and what to write up as a “proper paper”
Matt posted his response to the Aerosteon paper as a sequence of three blog entries even though he knew that what he had to say was substantial enough to make a paper. Why throw away a potential publication that would look good on the CV? Because he wanted to get it out there ASAP, and didn’t want to wait until all the media dust had settled. So he fought people off when they pestered him to publish it as a paper. He doesn’t really need to do it now, and he doesn’t really have time (especially since I keep badgering him about all the papers we’re supposed to be collaborating on). If we were starving for publications, we could turn a lot of SV-POW! posts into LPUs — but we’re not starving.
Let me explain this by taking a digression though the economics of file-sharing and the way labels persistently — maybe deliberately — misunderstand them. Let’s imagine for the sake of an example that a while back, I sent Matt the MP3s that make up Blue Oyster Cult’s awesome Fire Of Unknown Origin album. Now anyone with their brain switched on can see that the net effect of this on his music-buying pattern would be positive: if he really liked Fire, there is a fair chance that he would then have gone and bought a BOC album or two, or three — just as I’ve been buying Dar Williams albums like crazy since someone slipped me MP3s of Mortal City. The labels’ perception, however, is that instead I would have denied them a sale: that if I’d not sent the Fire of Unknown Origin MP3s, Matt would of course have bought his own legitimate copy, and so I’ve stiffed them out of $6.99 less whatever tiny slice they pass on to the artist. The misunderstanding here is that they think — or would like to think, who knows if they really believe this themselves? — that people’s music consumption is limited by the time we have available to listen to music, and that one way or another we will obtain enough music to fulfil that need: for free if possible, but by paying for it if necessary. But the truth is completely different: there would be zero chance of Matt’s ever buying any BOC album, since he’d never even heard of them (beyond Don’t Fear The Reaper, I guess) whereas in the hypothetical universe where I sent him the Fire MP3s, there is a non-zero chance. And the labels’ failure to understand that is because of a wholly incorrect model of what factor limits music listening.
Digression ends. Its relevance is this: in the same way, we are used to thinking that our ability to get papers published is limited by the number of publication-worthy ideas we have — so that every paper idea we “waste” on a blog entry is a net loss. In truth, ideas are cheap, and our ability to get papers published is actually limited by our throughput — our ability to find time to actually write those ideas up with sufficient rigour, prepare high-resolution figures, format the manuscripts for journals, wait through the review period, deal with the reviews, revise, resubmit, handle editorial requests, and so on and on. (That is especially true when the journal takes six months to come up with a rejection.) This is why Matt and I, like everyone else I know in palaeo who I’ve discussed this with, have huge stacks of POOP that we’ve not yet found time to convert into papers. So when we spend a paper-worthy idea on a blog entry, we’re not wasting it: we’re putting it out there (in an admittedly inferior format) when otherwise it would never have made it out there at all. The remaining issue is whether the time we spend on blogging an idea would have been better spent on moving a paper further towards publication. Maybe, sometimes. But you have to stop and smell the roses every now and again. So the real cost of SV-POW! for us is not the “waste” of paperable ideas, but the time we spend on writing it. I am guessing that in the time I’ve put into SV-POW! so far, I could have got two more papers out — certainly one. Has it been worth it? I think so, but it’s not a no-brainer. On the other hand, SV-POW! probably acts as a reader-funnel, so that when I do get a paper out, more people read it than otherwise would. How big that effect is, I don’t know, and I can’t think of a way to measure it.
How to cite blog entries: WebCite
One of the great things about writing for SV-POW! is that you can learn some really useful stuff from the comments; and the most useful comment I’ve seen so far is the one in which Cameron Neylon pointed us at WebCite (http://webcitation.org/). This is a superbly straightforward site that makes permanent archive copies of web-pages, and mirrors them around the world. In doing so, it deals with the problems of web pages being vulnerable to disappearance and prone to change. (In off-list emails with Matt, I had suggested that I might build something like this myself, as I am software engineer in my day job; I am delighted that these guys have done it properly instead.) So if you ever want to cite Matt’s second Aerosteon post in a journal, use the archive URL http://webcitation.org/5hPYTmWpW — and if you want to cite any other SV-POW! article, just submit its URL to WebCite yourself, and get back an archive URL which you can use. And tell all your friends about WebCite!
Oh, and by the way …
Here’s that photo of a monitor lizard getting its arse kicked by an elephant that you ordered:
- Lucas, S. G., Hunt, A. P. and Spielmann, J. A. 2006. Rioarribasuchus, a new name for an aetosaur from the Upper Triassic of north-central New Mexico. New Mexico Museum of Natural History and Science, Bulletin 37: 581-582.
- Parker, W. G. 2003a. Description of a new specimen of Desmatosuchus haplocerus from the Late Triassic of Northern Arizona. Unpublished MS thesis. Northern Arizona University, Flagstaff. 315 pp.
First off, thanks to everyone for reading, commenting on, and discussing the previous post. Seeing the diversity of opinions expressed has been interesting and gratifying for us, and we’ve learned a lot from you about how the blogosphere is changing science already. My own thoughts follow, Mike chimes in at the end, and Darren will probably have something to add soon, too.
The Intolerable Problem
Sometimes people push back on posts of mine they don’t like by telling me I’m out of bounds. Somehow, they say, I’ve crossed the boundary of what I’m allowed to write about. They are angry that I’m now writing about something outside my defined area.
I’m usually taken aback by this, because I didn’t realize I’d actually agreed to any boundaries.
Seth Godin, 2009, “Out of Bounds”
Several commenters have brought up what I call the Intolerable Problem, which is that people online can critique papers and present new evidence and arguments in a format that is impermanent and not peer-reviewed. It’s intolerable because on one hand such material is not currently (operative word) citable in most outlets, and on the other hand repeating it sans citation in peer-reviewed literature smacks of plagiarism (to some, but not to all). Although this material is potentially valuable it “doesn’t count” professionally (see exceptions below), which some professionals (not necessarily those who have commented here) regard as a fatal argument against posting it in the first place. But–and this is crucial–it’s only a problem for the tiny fraction of the audience who might want to cite the freely exchanged material. If you’re in that fraction, we value your attention and comments, but don’t assume we’re writing only for you, or to further our professional standing. We blog because we love this stuff, and even at a technical niche blog like SV-POW! the majority of readers probably don’t care at all whether the information is peer-reviewed or “counts” for professionals; they mostly care whether it’s right or not.
One obvious solution to the Intolerable Problem is to simply let people cite anything they want, including blog posts and DML posts. This is already starting to be implemented–see examples here and here and more discussion here. This runs into two problems: one is permanence (there is no guarantee that the cited post will be up forever, or that the author won’t revise it later in response to criticism [as I have done with this very post!]), which can already be solved using tools such as WebCite (thanks to Cameron Neylon for bringing this to our attention in a comment on the previous post).
The other problem is that citations serve two functions, which are to establish priority and to lend authority to an argument. Citing a blog post may establish priority, but some researchers will cavil at the idea that a blog post is an authoritative source (for varying combinations of researchers and blog posts). Whether they would be right to cavil I don’t know; in the end the market will decide. The market–that is, the desire to attain professional respect and avoid censure–will also dissuade authors from larding up their papers with citations to trivial or worthless online sources.
Those who are troubled by the free discussion of papers, evidence, and hypotheses online need to realize that:
- it’s been going on for a long time (15 years for the Dinosaur Mailing List);
- it’s only going to accelerate in the future;
- it’s not a problem for the vast majority of people participating in the discussions;
- any solution must involve accommodation to the reality of how people exchange information online (immediately, freely, globally, without prior filtering).
These discussions are not going to stop, and ignoring the output of such discussions (because they “don’t count”) will eventually become prohibitively expensive as those workers who insist on playing only by the old rules are outmaneuvered by others who find ways to use all available information regardless of its provenience or “respectability”.
Paper journals will die when online journals stop sucking
Most online publications are hampered by having to be identical to the dead-tree versions (no links, no embedded video, no rotating 3D PDF images, etc.). Eventually people will realize that it is counterproductive to keep hobbling the new medium to make it as slow, flat, and inefficient as the old medium. Once one journal takes the hobbles off, others will do the same rather than lose contributors to cutting-edge outlets. A few boutique journals may still produce flattened, gutted versions of the online publications on paper. People still fly biplanes, too. Paper-based journals will never be popular again and their existence will not stop people from doing whatever technology allows them to in the online venues.
Note that this does not even refer to the economic argument against dead-tree publishing, which has already relocated encyclopedias and newspapers from ubiquity to marginality or extinction.
I’m surprised that the revolution isn’t farther along already. The cage is open.
Whither peer review and editing?
This is all part of the Big Flip in publishing generally, where the old notion of “filter, then publish” is giving way to “publish, then filter.” There is no need for Slashdot’s or Kuro5hin’s owners to sort the good posts from the bad in advance, no need for Blogdex or Daypop to pressure people not to post drivel, because lightweight filters applied after the fact work better at large scale than paying editors to enforce minimum quality in advance.
Clay Shirky, 2003, “The Music Business and the Big Flip”
PLoS ONE is already going gangbusters, without peer-review prior to publication in many cases. The only holdup there is that the post-hoc review by commenters is not working out quite like they’d hoped, because few people are commenting. Not everyone agrees that there is a dearth of commenting at PLoS ONE; the larger point is that people publish there a lot and the community treats those pubs like they count, even though in many cases they are essentially un-reviewed.
[Update: I misunderstood peer review at PLoS ONE. Papers may be reviewed externally by people unconnected to PLoS, or by one or more unpaid Academic Editors, or by a combination. I had thought of the review by Academic Editors only, which accounts for 13% of papers, as a form of internal review, but according to Bora (down in the comments) it should count as external review. If you're happy with that--and the system is not without its critics--then all papers at PLoS ONE are externally reviewed prior to publication; even if you're not, pre-publication review by someone is still in place across the board at PLoS ONE, and 87% of papers are externally reviewed by people unaffiliated with PLoS. Post-publication commenting supplements rather than replaces pre-publication review.]
People do comment on blogs, all the time. Post-hoc review will work, in fact already does work, just fine on blogs. I predict that PLoS ONE clones of the future (PLoS TWO?) will emulate whatever features of blogs make people willing to comment on them but not on PLoS ONE v1.0.
Alternatively, the paucity of post-hoc commenting at PLoS ONE could be taken as further evidence that journal-mediated peer review, whether before or after publication, is dying just off to a slow start. I think that editorial control is not far behind. Both are locally extinct in some parts of the science publishing ecosystem, since people are already citing blogs.
Q: But–but–but? What about protecting the sanctity of the process? What about about guaranteeing respectability? What about prestige?
A: Hey, those questions would make a terrific opinion piece for your local newspaper–oops, too late.
I don’t deny that editors and peer reviewers often make significant contributions to the quality of published work. I just think that people will learn to get along without them if doing so allows faster and easier exchange of information. That was never possible on paper; it’s long been possible here.
A priori peer review and editorial control were invented because publications were scarce (in the Econ 101 sense of being limited) and there needed to be a barrier to entry. Now publication is instant, free, and global. Error correction and the assignment of value will still happen, but they’ll happen after publication rather than before, and they’ll be distributed rather than centralized.
Clay Shirky described the problem for newspapers and the recording industry as the existence of “cheap perfect copies”. An expanded but by no means exhaustive list for science publication includes:
- cheap perfect copies
- editable (but also archivable)
- linkable (both incoming and outgoing)
- globally distributed
- for free
- without pre-publication filtering
- with multimedia embeds (as opposed to including video etc. separately in the suppl. info.)
Online open-access journals currently take advantage of all of those capabilities except the last two. Newsgroup posts cover all the bases except the last one (so do tweets, despite the severe length limitations).
What covers everything? Blog posts. Which have the added advantage that people will comment on them without being asked.
But that’s not the whole simple story.
The center cannot hold–or can it?
So we’re looking at total chaos, right–a world where anyone posts anything they want, no one has any control, and no one knows how to find the good stuff? Well, two out of three, at least. I’m not worried about that last point, for two reasons.
First, thanks to search engines, aggregators, tags, tweets, links, etc., we already have pretty good tools for finding the good stuff. Those direction finders will get better even as the map gets more complicated.
Second, prestige will always be a motivator, so people will always compete to get into exclusive venues. Nature is not going away, although I think that in the near future they will decouple their online and print publications so that the former can take advantage of all the possibilities the web offers.
If I have a really good idea backed up with lots of data, I’ll keep trying to get it into the most prestigious outlet I can. I won’t put my best stuff on a blog just because it’s faster and less encumbered. Blogs probably won’t replace journals, at least not anytime soon. Rather, the spectrum of publishing possibilities will expand; below the category of Least Publishable Unit we’ll add Most Bloggable Unit and so on down to Least Tweetable Unit, and the new categories will interpenetrate with the old over time.
How nice for me
Well, what a striking coincidence that Mr. Paleo Blogger looks into the ole digital crystal ball and sees “bloggy with a 90% chance of exactly-what-he’s-already-doing”.
I can’t claim to be either uninterested or unbiased in all of this. But I am new to actually thinking about the implications. I hadn’t been to most of the above links or had any of these thoughts as of a week ago. When Casey first e-mailed me six days ago, I replied:
If you’re curious, here’s the short short version of my thoughts: science bloggers critique published papers and blog about unpublished observations all the time. Our post-paper run of posts might be an extreme or even vulgar example, and it might fire more discussion about “what counts?”, but I don’t see it as being different in kind from what many science bloggers do. Papers are papers and blogs are blogs, and I never intended to blur the lines. If people feel that all the blog posts only count as “crap some guys wrote on the internet” and that they can be safely ignored, that’s fine with me. If they think the blog posts deserve some higher level of recognition a la “what counts?”, then I’m honored, but that’s extra value that others are investing in our blog, and not anything that we’ve knowingly sought. I suppose you could turn around and say that I’m trying to have my cake and eat it, too, first with all the pro-paper blogging and now with this “I’m innocent” schtick. I don’t know what the answer is, but I know that I’m too tired to figure it out tonight. All the more reason to have an open conversation about this stuff.
Now I realize that the lines between papers and blog posts are blurring, and whether we mean to or not, we SV-POW!sketeers are contributing (Darren’s doing double duty thanks to Tet Zoo). I still think that the investment of blog posts with respectability, value, citability, or whatever rests entirely with readers, and always will. Options range from treating posts like papers to treating them like bar conversations to treating them like spam. You decide.
Also, I tried to keep the writing above value-neutral but probably failed. It’s hard not to get a bit evangelistic about the potential advantages of online publication and online everything else, a tendency I call DISSUADE: Da Internet Shall Save Us All Dead-trees Excepted. Getting published in science hasn’t always been easy up until now, but the process has been relatively clear and familiar. And stable, on decadal and even centennial timescales. Everything about scientific publication is about to get much more fluid and much less clear, and it will probably stay that way for a long time, and it may stay that way forever. Not all of the changes will be for the better, and it may be hard to decide what’s better and what’s worse until we look back with some perspective. Mechanical looms were bad for weavers but good for everyone else. I think many of the changes discussed in this post and the previous comment thread are likely, and some are inevitable.
Set against the shiny digital future is the inertia of the academy and those of us who roost there. I’m not going to stop publishing papers in dead-tree journals (although I will never publish in a journal that doesn’t provide PDFs to authors). Heck, I’m not even going to stop publishing in closed-access journals, some of which are run by societies I admire and want to participate in (after all, everything is open anyway). At the same time I will keep blogging, and while I will frequently bring up technical stuff I don’t want to publish more formally (at least not yet), I will try not to deliberately blur the lines any more than I already have. I don’t need to; the web is already blurring them faster than most of us can keep up.
Oh, about that mystery vert…
…at the end of the post Necks Lie. Nima called it–good spot on the split neural spine. It’s a mid-cervical of Barosaurus, AMNH 6341, in the big bone room (well, one of many big bone rooms) at the American Museum of Natural History in New York. A cast of this vertebra makes up part of the neck in the awesome mounted skeleton in the museum rotunda. Here’s that skeleton, with Mike for scale.
Matt is much more ready than I am to throw away peer-review, editorial control, and journals in general. Sometimes, the reasons that things are the way they are, are good ones; it’s not in the interests of professional iconoclasts like Clay Shirky and Cory Doctorow to point that out or to discuss the strengths of how things are today, but that doesn’t mean we have to accept their arguments as uncritically as (say, to pick a name out of the air completely at random) Matt.
Anyway, happily, G. K. Chesterton foresaw the abolition of journals in favour of blogs, and commented thus:
Suppose that a great commotion arises in the street about something, let us say a lamp-post, which many influential persons desire to pull down. A grey-clad monk, who is the spirit of the Middle Ages, is approached upon the matter, and begins to say, in the arid manner of the Schoolmen, “Let us first of all consider, my brethren, the value of Light. If Light be in itself good–” At this point he is somewhat excusably knocked down. All the people make a rush for the lamp-post, the lamp-post is down in ten minutes, and they go about congratulating each other on their unmediaeval practicality. But as things go on they do not work out so easily. Some people have pulled the lamp-post down because they wanted the electric light; some because they wanted old iron; some because they wanted darkness, because their deeds were evil. Some thought it not enough of a lamp-post, some too much; some acted because they wanted to smash municipal machinery; some because they wanted to smash something. And there is war in the night, no man knowing whom he strikes. So, gradually and inevitably, to-day, to-morrow, or the next day, there comes back the conviction that the monk was right after all, and that all depends on what is the philosophy of Light. Only what we might have discussed under the gas-lamp, we now must discuss in the dark.
- Heretics (1905).
I don’t know guys. I like your blogs, and your papers are fine. And I liked this paper. And I’m a fan. But it looks to me that you blogged about far more data, in- or not in support of your paper than you actually presented in your paper. So,…wtf? The posts on Dinomorph far exceeded your (or any) published rebuke. Your explanation (and honorable erred parts) of the semicircular canal data also exceeded that actual published part too, with extra photos, description etc. (is that error going to be OA published too?) Also additional pix of necks (e.g., Nigersaurus), and not only from sauropods that would have
potentially bettered the original pub. So what’s fair? Why weren’t
these data also included in the publication? Maybe it’s not my business and was taken up in review…I don’t know. Frankly, none of this blog stuff really counts in the peer-reviewed world of “real” publications. Its not like this blogging and comments all count as Supplementary Data either. But also, I’m obviously here commenting on it, so also crossing into the fray…But who really cares about all this discussion? Its no different than the DML or any other noise in the internet world (or is it). Similar to what Paul Barrett was posting on Tet Zoo…what counts? Why take up arguments here, when they should (maybe?likely?) be taken up more formally and privately.
If you’re going to air all this additional data and unreviewed
opinion, then I think this discussion is important.
I think this phenomenon of the sauropod neck paper is really
interesting. We have 3 scientists that published a paper, and then, thanks to their current blogosphere cred, basically unleashed a hype not seen in this way previously that I can remember. Maybe that’s the interesting part? and kudos. But interestingly…we’re seeing this intersection of traditional publication (OA or not), blogosphere description, and perhaps, almost certainly, excellent self-promotion.
I’m still a fan. I think this paper is generally solid. But I’m
particularly interested in this phenomenon and hope this is a fair
place to raise it.
The comment field is open, and we SV-POW!sketeers are going to refrain from commenting for a couple of days to let the conversation develop unfettered.
We are genuinely curious to know what you think.
June 5, 2009
Man, I hate making mistakes. The only thing worse than making mistakes is making them in public, and the only thing worse than that is finding them in published papers when it’s too late to do anything about them. About the only consolation left–if you’re lucky–is getting to be the one to rat yourself out (we have to do this a lot). So here goes.
In our figure 4 (from Taylor et al. 2009) we showed the skulls of three sauropodomorphs, Massospondylus, Camarasaurus, and Diplodocus, posed with horizontal semicircular canals (HSCCs) level, angled 30 degrees above horizontal, and angled 20 degrees below horizontal, as it is written (by Duijm 1951). We also showed the angle of the occipital condyle when the HSCCs are level; if the craniocervical joint was in osteologically neutral pose (ONP), that line would indicate the angle of the anterior cervicals.
Trouble is, we put the neck lines for Diplodocus and Camarasaurus in the wrong places.
As any idiot can see from Sereno et al. (2008: fig 1), the brain, brainstem, and occipital condyle form a line that runs from roughly the upper part of the orbit (in lateral see-through view) out the back of the head. Now if you look at our fig. 4 you’ll see that the ONP lines for Camarasaurus and Diplodocus are much too inclined, so that if the brain was in line with the anterior neck–which it should be, in ONP–it would be sticking out the back of the head.
If that doesn’t make sense, just look at the above illustration, imagine the brain and spinal cord in a straight line parallel to the black neck line but also dorsal to it, and you’ll see that the brain would be outside the skull. Those incorrect neck lines don’t represent impossible postures, but they don’t represent ONP, either.
Here’s a corrected up version of the figure to show what I mean. The black lines are still the ONP neck lines, and now I’ve put in shadowy necks at +30 and -20 to go with the shadowy heads. The 50 degree spans marked out by the shadowy necks are the ranges within which the neck could articulate in ONP with skulls stuck in the 50-degree “Duijm window”.
Caution: it is very easy to misread the shadowy necks as showing a range of movement within an individual; in fact, the neck lines are ‘anchored’ to the skulls in ONP as the skulls rotate through the 50 degrees allowed by the HSCCs. They are not individual movement but the possible range of taxonomic variation in HSCC orientation according to Duijm (1951).
Worth noting here is the likelihood that Massospondylus had a more elevated neck than any of the neosauropods studied so far–certainly a finding at odds with the traditional depictions of basal sauropodomorphs. (It is just a likelihood, though, since the top, neck-wise, of Massospondylus‘s Duijm window overlaps with the windows of the other taxa a bit.)
In this version I’ve gone one step farther and included Nigersaurus (modified from Sereno et al. (2008: fig 1). Nigersaurus differs from Diplodocus in the angle of the face from the HSCCs and occipital condyle, not in the angle between the HSCCs and the occipital condyle, which is remarkably similar in Camarasaurus, Diplodocus, and Nigersaurus. This suggests that Nigersaurus held its head differently than other sauropods, but not necessarily its neck.
Keep in mind, though, that the difference in facial angle between Diplodocus and Nigersaurus is less than 50 degrees, and that some of the head postures in the respective Duijm windows of the two taxa are identical. So we can’t say for certain that Nigersaurus held its head differently than Diplodocus; it is possible that they held their heads at the same angle and that Nigersaurus just carried its HSCCs at a different angle. If that were the case, the neck of Nigersaurus would have been more inclined than that of Diplodocus. I’m not arguing that that’s likely–it seems perfectly plausible that the two taxa might have held their necks similarly and their heads differently, as suggested above–I’m just pointing out the very wide range of possibilities allowed by the data. To reiterate one of the points of the paper, HSCCs aren’t useless for determining habitual head posture, they just can’t narrow things down very far on their own.
Also note that some of the neck postures allowed by the Duijm window have the anterior cervicals running down, below horizontal, not up. And many of the allowed neck postures for the neosauropods are close to horizontal. So, we were wrong and HSCCs + occipital condyles show that most sauropods held their necks close to level and not strongly elevated after all, right?
Onward and Upward, or Down in Flames?
Not so fast. Remember that all of the neck lines in the above figures show the angle of the anterior neck if the neck was in ONP with the skull. But Vidal et al. (1986) found that the skull is habitually flexed on the neck, even in lizards, and we have since verified this for salamanders, turtles, and more. And sometimes the flexion is dramatic.
Our figure 1 (from Taylor et al. 2009) shows the cranium, cervicals, and first few dorsals from a hare in ONP and in the posture shown by Vidal et al. (1986: fig. 4b). The difference between the anteriorly-directed ONP pose and the backward-leaning Vidal-compliant pose is striking. I measured the angle between the cervical column and the maxillary toothrow to be ~110 degrees in the ONP pose and ~70 degrees in the Vidal-compliant pose (try it yourself with Paint or Photoshop, or download some free image manipulation software). That means the head is flexed on the neck by 40 degrees! That is a big angle. If sauropods did the same, you could take the neck lines shown above and crank them down by 40 degrees (remember that the heads are “fixed” into the 50-degree Duijm windows allowed by the HSCCs), which would make Mike’s elevated Diplodocus look not just achievable, but perhaps even conservative.
Where does all that leave us? In sauropods for which HSCC orientation is known, putting the HSCCs level the anterior neck is still inclined, and even with the HSCCs angled 20 degrees down the ONP neck would only be slightly below horizontal, and if the head was Vidal-compliant (strongly flexed on the neck), the neck would have to be above horizontal. So heads still tell us about necks, and in particular they tell us that the necks angled up. Our neck lines for Camarasaurus and Diplodocus are not correct for ONP, but probably represent attainable postures. My first head ‘n necks post has the angles too exaggeraged for ONP, too, but again all of those poses are not just possible but likely if the head was flexed on the neck.
We owe mad props to Brian Engh, a.k.a. The Historian, who burst on the paleo-rap scene with a rap video about crocodilian predation and almost certainly the first ever kung-fu rap video to name-check titanosaurs. Brian stumbled across Mike’s extra goodies page for the new paper about week before the paper was due out, and kindly suppressed the information until after D-Day. You can and should download his entire album, Earth Beasts Awaken (open access, yo), and kick it old school.
Congratulations to Francisco “Paco” Gasco, who just got funding for a PhD to do a complete morphological and paleobiological workup on the giant Spanish sauropod Turiasaurus. You’ll be hearing more about Paco in the not-too-distant future, we promise.
Finally, here’s that video of an elephant grabbing an ostrich by the neck that you ordered.
The End of the Beginning?
This brings us to the end of ten solid days of new posts, which is a new record for us and one not likely to be broken for a long time, if ever. We never planned to do all this; in the beginning we each were going to contribute one post and that would have been that. But we kept finding things that we felt needed to be discussed.
As all of us have been saying in every available medium, this is not the end of anything. The sauropod neck posture debate is not over; in a few years we may look back and see that in 2009 we were still stumbling to the real starting line. We don’t think this stuff is unimportant or unknowable, and we’re going to keep working on it, and we hope lots of others do as well.
We’ll see you out there.
- Duijm, M. 1951. On the head posture in birds and its relation to some anatomical features. II. Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen, Series C 54: 260–271.
- Sereno, Paul C., Jeffrey A. Wilson, Lawrence M. Witmer, John A. Whitlock, Abdoulaye Maga, Oumarou Ide and Timothy A. Rowe. 2007. Structural Extremes in a Cretaceous Dinosaur. PLoS ONE 2 (11): e1230 (9 pages). doi:10.1371/journal.pone.0001230
- Taylor, M.P., Wedel, M.J., and Naish, D. 2009. Head and neck posture in sauropod dinosaurs inferred from extant animals. Acta Palaeontologica Polonica 54 (2): 213–220.
In case you haven’t heard, Taylor et al. (2009) recently argued that sauropods naturally held their cervico-dorsal junctions in extension, and their cranio-cervical joints in flexion… at least, when they weren’t foraging, feeding or engaged in other such activities [if you need help with those terms please see the Tet Zoo article here].
Given that we here at SV-POW! are predominantly interested in sauropods, and given that the amazing necks of these animals have long been such a source of debate, it stands to reason that sauropods might get used as the ‘poster children’ or exemplars for any particular argument about neck pose in fossil tetrapods. However, as we’ve said here and there – I certainly mentioned it in my Tet Zoo article on the subject – the contention (that cervico-dorsal junctions are maintained in extension, and that cranio-cervical joints are maintained in flexion) holds true for all terrestrial amniotes and, to a degree, all crown-group tetrapods. In this article we’re going to do something a little odd for SV-POW! – we’re going to look at other fossil amniotes to see if and how this affects them. Have any of them also been reconstructed in poses that are not compliant with the data from living animals?
The short answer is yes, yes they have.
First off, fossil mammals mostly get by ok, which is what you’d expect given that they are generally very similar to their extant relatives. Likewise, there aren’t any fossil birds that have been reconstructed incorrectly, and again you’d hope not given that they’re generally highly similar to extant forms. The extinct moa from New Zealand (that’s moa in the plural sense) are sometimes shown standing at rest with non-extended cervico-dorsal junctions, but with extremely strong extension in the anterior part of the neck that makes up for this (Worthy & Holdaway 2002). While extension at the cervico-dorsal junction may be subtle or absent in living ratites when they are feeding or foraging, in relaxed individuals extension at the neck base is indeed present.
Stegosaurs really need a makeover
What about other dinosaurs? Here’s where we do find quite a few reconstructions that contradict our contention. For a start, basal sauropodomorphs – the animals conventionally lumped together as prosauropods – have often been shown with non-extended cervico-dorsal junctions and fully extended cranio-cervical junctions: that is, with necks that emerge in a straight line from the body, and heads that have their long axis parallel to that of the neck. Classic examples include Kermack’s reconstruction of the animal formerly known as Thecodontosaurus and Weishampel & Westphal’s Plateosaurus. There are many others.
Historically, non-avian theropods have been depicted with elevated necks, flexed cranio-cervical junctions and all that. So far so good. One specific exception does come to mind however: Tarsitano (1983) produced a truly awful theropod reconstruction in which the neck was shown as straight and with a non-extended cervico-dorsal junction. The latter is a no-no, and so is straightening the neck this much, as the shapes of the centra and neural arches show that the cervical vertebrae of theropods were held elevated and in a gentle S-curve (see Molnar & Farlow 1990). A few artistic reconstructions of non-avian theropods have given them non-elevated necks (Neave Parker’s megalosaur picture from the 1970s comes to mind), and if you look at the allosaurs that featured in Walking With Dinosaurs you’ll note that their cranio-cervical junctions are extended, not flexed as they should be.
On to ornithischians. It was difficult to keep a tight lip back in February 2009 when the long-necked stegosaur Miragaia longicollum was published. Like the WWD diplodocoids, Miragaia was given a non-extended cervico-dorsal junction and extended cranio-cervical junction: in other words, its neck and head were illustrated projecting forwards in a straight line, as a continuation of the animal’s dorsal column (Mateus et al. 2009). Based on what we know about living animals, it’s more likely that the cervico-dorsal junction was extended, and that the cranio-cervical junction was flexed: in other words, that the neck was strongly elevated relative to the dorsal vertebrae, and that the head was held at an angle to the neck. Given the remarkable length of its neck, this at least makes it possible that Miragaia was a high-browser. I look forward to seeing artistic reconstructions that show this animal with its head held up above its back, rather than extending forwards and parallel to it (actually, I’ve already seen two, but you know what I mean).
In fact, like sauropods, stegosaurs have been flat out abused by palaeontologists, with non-extended cervico-dorsal junctions and fully extended cranio-cervical junctions being the norm across more than 100 years of description and reconstruction. And don’t use the excuse that these reconstructions are all meant to show the animals engaged in feeding or foraging: they’re not. Many of them clearly depict the animals standing, in relaxed poses, and doing nothing. Marsh started it in 1891: he showed the skull of Stegosaurus armatus (then S. stenops) fully extended, rather than flexed, on the neck, and showed the neck continuing in (approximately) a straight line from the dorsals. This reconstruction was hugely influential, of course, and even today the popular conception of the stegosaur – with its horrible over-arched back and down-sloping tail – is based on Marsh’s drawing. Later stegosaur reconstructions by Lull and Gilmore perpetuated the idea of non-extended cervico-dorsal junctions and fully extended cranio-cervical junctions in Stegosaurus (see Czerkas 1987 for a review of stegosaur life reconstructions), and the same posture was later reconstructed for Huayangosaurus, Kentrosaurus, Tuojiangosaurus and others (see Galton & Upchurch 2004).
Those stegosaur reconstructions you can see in some museums – some of which show the cranio-cervical junction in slight hyper-extension (look at the Tuojiangosaurus shown here) – are flat-out horrible and totally contradict the data we have from neck and head posture in extant amniotes (Taylor et al. 2009). In recent decades, reconstructions by artists like Stephan Czerkas and Greg Paul have given stegosaurs raised necks where the cervico-dorsal junction is extended in proper fashion (as per the data from living amniotes). I get the impression, however, that such reconstructions have not been taken seriously by ‘mainstream’ palaeontologists, at least some of whom still seem to think that stegosaurs walked around with their heads two inches off the ground.
Similar mistakes have been made with ankylosaurs: most classic reconstructions show non-extended cervico-dorsal junctions where the neck emerges in a straight line or even slopes downwards, and cranio-cervical junctions that are in full extension. This goes for Ken Carpenter’s Euoplocephalus [shown in composite above] and Sauropelta, Richard Lull’s Nodosaurus, and others (Lull 1921, Carpenter 1982, 1984). Again, the reconstructions that show these neck and head postures do not definitely show the animals in feeding, foraging or searching postures: they are meant to depict the ‘normal’ (viz, relaxed) pose for the animal. A gently elevated neck with an extended cervico-dorsal junction and a flexed cranio-cervical junction is, again, what we should expect given what living animals do, and this has been correctly portrayed by some.
Other ornithischians have generally been reconstructed accurately (at least as goes neck and head posture), but there are, however, a few ceratopsian reconstructions showing non-extended cervico-dorsal junctions and fully extended cranio-cervical junctions. Granger & Gregory (1923) reconstructed Protoceratops in this manner, for example, and ceratopsids have sometimes been shown this way too (Lull 1933). Again, the reconstructions I’m referring to are meant to show normal, relaxed poses, rather than feeding or foraging poses, so criticism is justified. Putting extension into the ceratopsian cervico-dorsal junction raises the head somewhat, such that the top of the frill is now higher than the top of the back rather than lower than it. Notably, some articulated skeletons are displayed this way: the Centrosaurus panel-mount AMNH 5351, shown here, is one of the best examples. Lull thought that the neck had been elevated too much and that the neck posture ‘is that of death rather than that of life’! Peter Galton’s Hypsilophodon (which has mostly been superseded by Greg Paul’s reconstruction these days anyway) should also be considered suspect in view of the strongly extended cranio-cervical junction (Galton 1971, 1974), but the animal was clearly meant to be running at speed, so you could argue that it was shown holding its head and neck in a decidedly un-relaxed pose.
I should point out again at this point that our contention (that cervico-dorsal junctions should be shown in extension in a relaxed animal, and cranio-cervical junctions should be shown in flexion in a relaxed animal) is a hypothesis. It’s possible (unlikely perhaps, but possible) that some stegosaurs, or ankylosaurs, or therapsids, or whatever, did some funky stuff with their occipital condyles or vertebrae and evolved a relaxed head and neck posture different from that of living amniotes, and indeed (as we’ll see in a moment) there surely are at least some exceptions within Amniota. However, if you think a given animal represents a special case, you’re gonna have to demonstrate it.
Shock horror, marine reptiles on SV-POW!
Elsewhere among Reptilia, the data from living lizards and crocodilians indicates that, generally speaking, we should expect fossil forms to hold their necks elevated at moderate angles of between 20-40° relative to the dorsal column when in normal, relaxed pose. Many fossil, non-dinosaurian archosaurs (like rauisuchians and aetosaurs) have been reconstructed this way (mostly because people have looked at living crocodilians when reconstructing these animals), as have fossil squamates and many others.
We do, however, have a contradiction of sorts when we come to sauropterygians (the plesiosaurs and their relatives). Reconstructions of plesiosaurs have evolved in similar fashion to those depicting sauropods: some old reconstructions (some, not all) depict them with extended cervico-dorsal junctions and flexed cranio-cervical junctions (such reconstructions typically show the animals sticking their necks well up out of the water and peering around) (e.g., Williston 1914), but many others show them with non-extended cervico-dorsal junctions and fully extended cranio-cervical junctions. In other words, with the neck and head continuing in a straight line from the dorsal column.
Contradicting the idea that plesiosaurs looked down on their prey from above is the fact that their orbits often face slightly or strongly upwards, and there are also indications from their narial and ear anatomy that they were specialised for detecting sensory cues in water, not in air (Cruickshank et al. 1991, Storrs & Taylor 1996). Furthermore, their high-density, often pachyostotic skeletons indicate that they were negatively buoyant animals that were trying their hardest to stay submerged and beneath the surface. All of this indicates that plesiosaurs were subaqueous predators that mostly kept their necks and heads beneath the surface of the water (except when breathing). This makes it very unlikely that their necks were elevated, and indeed – in strong contrast to sauropods and other dinosaurs – there are indications from their vertebral anatomy that neck elevation was not possible in the group (in elasmosaurs, for example, the neural spines on both the cervicals and dorsals are tall and sub-rectangular and it’s difficult to imagine how this would have allowed anything more than extremely subtle extension at the cervico-dorsal junction). So I am going to go out on a limb here (or, more accurately, I’m going to agree with everyone who works on plesiosaurs) and say that plesiosaurs did not hold their necks in the same manner as the extant amniotes that we looked at (Taylor et al. 2009). Is this because they were aquatic, and hence not under the same gravitational constraints as terrestrial amniotes? That looks likely, but we really need to thrash this out once and for all: further work on this is obviously needed, and perhaps it will appear soon. I know from many discussions that plesiosaur researchers talk as much about long necks as sauropod researchers do.
Finally – dicynodonts and other synapsids
Moving now well away from dinosaurs and archosaurs and even reptiles, I’ve had non-mammalian synapsids on my mind an awful lot during all of this. While many of them have relatively short necks, members of some groups have still been shown in downright unlikely postures. Dinocephalians have consistently been shown (correctly) with extended cervico-dorsal junctions and flexed cranio-cervical junctions, so those reconstructions of such things as Titanophoneus and Moschops with their necks held high and their heads at an angle are correct based on the data from living amniotes. However, some reconstructions of some caseids (Stovall’s Cotylorhynchus), dicynodonts (I’m looking at you, Watson’s rendition of Lystrosaurus [shown at top of composite image used above] and Cluver’s Cistecephalus) and gorgonopsids (Colbert’s Lycaenops, for example; shown below) have the cranio-cervical junction in extended or even hyper-extended pose, which again is a total no-no unless there is evidence to the contrary. While some of these animals have been reconstructed in walking or running poses (and hence might be holding their necks and heads in special searching or foraging poses), plenty of others are shown standing on all fours, in relaxed, ‘normal’ poses, so their unusual neck and head poses are, we can assume, meant to be the relaxed, ‘normal’ poses (further examples include King’s Dicynodon and Dinodontosaurus).
The relatively short necks of these animals mean that, even with the cervico-dorsal junction in full extension, the neck is only elevated by a slight and thoroughly believable 20-40° relative to the dorsal column. Similarly, showing the cranio-cervical junction in flexion is no big deal, as all it does is rotate the skull such that its long axis is at an angle to the neck, rather than acting as a straight-line continuation of it. It seems that more extreme cervico-dorsal extension and cranio-cervical flexion evolved within Mammalia, and hence that non-mammalian synapsids were more like other ‘average’ amniotes in head and neck posture. Nevertheless – again – reconstructions that show the neck and head as straight-line extensions of the back should be considered inconsistent with what we know of neck and neck posture in living amniotes.
We really hope that our paper will inspire some much-needed debate, and instigate some new work. As you’ll know if you’ve been following the comments on blogs and such, and the media coverage we’ve been getting, there’s every indication that this is exactly what will happen. But what makes this work of particular interest to people in general – and not just to specialists who spend their time worrying about cervical rib morphology and its correlation with functional morphology, or whether the bifurcate neural spines of some sauropods are homologous with the single neural spines of others, and so on – is that it has a real and obvious effect on the life appearance of a fossil animal. And, as I’ve tried to show here, our hypothesis extends beyond the limits of Sauropoda. Stegosaurs and dicynodonts need never look the same way again.
- Carpenter, K. 1982. Skeletal and dermal armor reconstruction of Euoplocephalus tutus (Ornithischia: Ankylosauridae) from the Late Cretaceous Oldman Formation of Alberta. Canadian Journal of Earth Sciences 19, 689-697.
- Carpenter, K. 1984. Skeletal reconstruction and life restoration of Sauropelta (Ankylosauria: Nodosauridae) from the Cretaceous of North America. Canadian Journal of Earth Sciences 21, 1491-1498.
- Cruickshank, A. R. I., Small, P. G. & Taylor, M. A. 1991. Dorsal nostrils and hydrodynamically driven underwater olfaction in plesiosaurs. Nature 352, 62-64.
- Czerkas, S. A. 1987. A reevaluation of the plate arrangement on Stegosaurus stenops. In Czerkas, S. J. & Olson, E. C. (eds) Dinosaurs Past and Present, Volume II. Natural History Museum of Los Angeles County/University of Washington Press (Seattle and Washington), pp. 82-99.
- Galton, P. M. 1971. Hypsilophodon, the cursorial non-arboreal dinosaur. Nature 231, 159-161.
- Galton, P. M. 1974. The ornithischian dinosaur Hypsilophodon from the Wealden of the Isle of Wight. Bulletin of the British Museum (Natural History) 25, 1-152.
- Galton, P. M. & Upchurch, P. 2004. Stegosauria. In Weishampel, D. B., Dodson, P. & Osmólska, H. (eds) The Dinosauria, Second Edition. University of California Press (Berkeley), pp. 343-362.
- Granger, W. & Gregory, W. K. 1923. Protoceratops andrewsi, a pre-ceratopsian dinosaur from Mongolia. American Museum Novitates 72, 1-9.
- Lull, R. S. 1921. The Cretaceous armored dinosaur, Nodosaurus textilis Marsh. American Journal of Science 1, 97-126.
- Lull, R. S. 1933. A revision of the Ceratopsia or horned dinosaurs. Memoirs of the Peabody Museum of Natural History 3, 1-175.
- Mateus, O., Maidment, S. C. R. & Christiansen, N. A. 2009. A new long-necked ‘sauropod mimic’ stegosaur and the evolution of the plated dinosaurs. Proceedings of the Royal Society of London, Series B (doi:10.1098/rspb.2008.1909)
- Molnar, R. E & Farlow, J. O. 1992. Carnosaur paleobiology. In Weishampel, D. B., Dodson, P. & Osmólska, H. (eds) The Dinosauria. University of California Press (Berkeley), pp. 210-224.
- Storrs, G. W. & Taylor, M. A. 1996. Cranial anatomy of a new plesiosaur genus from the lowermost Lias (Rhaetian/Hettangian) of Street, Somerset, England. Journal of Vertebrate Paleontology 16, 403-420.
- Tarsitano, S. F. 1983. Stance and gait in theropod dinosaurs. Acta Palaeontologica Polonica 28, 251-264.
- Taylor, M. P., Wedel, M. J. & Naish, D. 2009. Head and neck posture in sauropod dinosaurs inferred from extant animals. Acta Palaeontologica Polonica 54, 213-220.
- Williston, S. W. 1914. Water Reptiles of the Past and Present. University of Chicago Press, Chicago.
- Worthy, T. H., Holdaway, R. N. 2002. The Lost World of the Moa. Indiana University Press, Bloomington, Indiana.
June 3, 2009
Here at SV-POW! Towers, we often like to play Spot The T. rex — a simple drinking game that can be played whenever you have supply of palaeontology-related news reports. Each player in turn takes a report off the stack, and if T. rex is mentioned anywhere in the report, the player drinks. We lay in a lot of beer when we play this game, because as it turns out, T. rex is nearly always mentioned (and nearly always spelled “T-Rex”, no italics, no full stop, gratuitous hyphen, capitalised trivial name). For example, suppose someone publishes an innocent paper arguing that a particular Eocene clam was an obligate scavenger: then the story in the press will be “… just as has been argued for the terrifying T-Rex, which had teeth like steak knives”. Or if someone names a new Miocene rodent, it will be introduced as “… which lived 50 million years after the terrifying T-Rex, which had teeth like steak knives”. (Drink twice if the steak knives are mentioned. Three times if they are described as “banana-sized”.)
So we didn’t feel our neck-posture paper was real until it had somehow been tied in with T-Rex. Happily, the Great North Museum came to the rescue: by coincidence, they unveiled their T. rex cast the weekend before the paper came out, and the Sunday Sun wanted our opinion on the way the neck had been mounted. Here’s their mount (not quite ready to exhibit):
Of course, everything we said about the necks of sauropods in the paper also applies to every other extinct land vertebrate — we only concentrated on sauropods because (A) they are the group whose neck posture has been claimed to depart from the tetrapod norm, and (B) they are cool. In particular, non-avian theropods such as T. rex are in the same extant phylogenetic bracket as sauropods are (i.e. birds plus crocs), so we’d expect strong extension at the base of the neck and strong flexion at the head joint in habitual pose.
So I replied that “the Newcastle mount has the neck and torso in more of a straight line [than a Vidal-compliant posture], which would probably not have been the habitual pose. It looks to me as though this animal is crouching down to take a drink”, and I’m pleased that the resulting news story included a rather gracious response from the GNM curator.
I don’t know whether the notoriously litigious Disney corporation would be so mellow, though, regarding their truly horrible mount of a cast of “Sue”:
I’m really not sure what the people who mounted this were getting at: unlike the Great North Museum mount, the legs are erect, so it’s not going into or coming out of a crouch; and it’s not going into a drinking posture, because the head is pointing straight forward. But for some reason, it’s below shoulder height.
Here’s how it should be done:
It’s good to see that the biggest natural history musuem in the world is ahead of the curve, and has its T. rex mount in a pose consistent with how other land vertebrates habitually hold their necks.
I leave you with the news the T. rex‘s neck is pathetic. Here is the skull and neck of that same AMNH mount, composited with a single cervical vertebra (C8) of Sauroposeidon. Please note that the Sauroposeidon cervical is way longer than the whole T. rex neck.
No references today!
[You don't need to be told the reference for Taylor et al. (2009) again, do you?]
June 2, 2009
Because the appearance of accuracy has an irresistible allure, non-specialists frequently treat these estimates as factual.
–Graur and Martin (2004: p.80)
Prologue: Why We Hatin’?
Between the first DinoMorph post and this one, it may seem like we have it in for DinoMorph, like we’re trying to discredit the method or bury it. We’re not anti-DinoMorph at all. We really want it to work, because 3D modeling is probably going to be the only way to explore some problems we care about (like the breathing mechanics of an articulated sauropod torso), and so far DinoMorph seems to be farther along than any of the alternatives. It is also worth remembering that building 3D digital dinos for scientific purposes is still in its infancy, and that the VP community has barely gotten started exploring the possibilities. The field has great promise. But we also have to be realistic about limitations in the source data (see Mike’s post) and about the accuracy and precision of the results (this post). We hope that these posts will start constructive conversations and inspire more work to improve the science.
Intro: Accuracy and Precision
Accuracy is how close to the real value a measurement is, and precision is how close repeated measurements are to each other. Say it’s 100 degrees F outside, which it may be for some of you. If you have four thermometers and they read 90, 95, 105, and 110, then the mean is 100. The accuracy of the aggregate setup is high, but the precision is low (big error bars). If, on the other hand, your thermometers read 94.2, 93.8, 94.6, and 93.4, then they are precise (tight grouping) but inaccurate (not centered on the real value)
Oh Error Bars, Where Art Thou?
Here’s what 2 degrees (angular, not temperature) looks like:
It’s not a big measurement. If I was measuring the range of movement (ROM) of a single joint in one individual, like an elbow or shoulder, and I got a precision of plus or minus 2 degrees over repeated movements, I’d be pretty happy. If I got that level of precision on, say, the left knee, in ten different people, I’d start worrying that I was in the Matrix.
All eusauropods have at least 12 cervical vertebrae, and diplodocids have at least 15 (Barosaurus probably has 16, but there are no complete necks so it’s hard to be sure). What happens if we propagate an error of plus or minus 2 degrees down the neck of Diplodocus?
None of these are supposed to correspond to any particular pose in life. I just lined up all the cervicals as straight as I could get them, and then rotated each joint between C3 and C15 by 2 degrees. I left the occipital condyle and C1-C3 in a straight line because I felt the point was made, but the head could be rotated up or down by another 6 degrees if one so chose. Again, this is not an ROM, this is just an error of plus or minus 2 degrees across each of 12 intervertebral joints.
Now let’s look back at the neutral pose and estimated ROM of the neck in the CM 84/94 composite skeleton of Diplodocus (Stevens 2002: fig. 6a):
Notice that the model poses are shown with perfect precision, and no allowance for error. Now, look back up at the first picture to get an idea of what 2 degrees of error looks like, and then try to mentally apply it to each of those three poses. It’s not easy to picture, but in my mind’s eye the three neck poses dissolve into a fuzz of probabilities, like the electron cloud around the nucleus of an atom.
How precise is DinoMorph? Or rather, given that the guts of the program probably allow for Jupiter flyby levels of precision, how precise is any given result, based on the interaction of raw data, necessary but unverified controlling assumptions (see below), and the algorithm itself? Can we really rule out an error of plus or minus 2 degrees per joint? What about 1 degree per joint? What about 5? This is a problem of precision, and it would still exist even with an absolutely perfect neck that was 100% complete and entirely undistorted (which we ain’t got).
It’s possible that the current version of the program doesn’t allow these kinds of error calculations. That’s fine–I realize that DinoMorph, like all of science, is a work in progress. But I’d like to know up front that there is no provision for determining the precision, so I could delay asking the question. And at some point, it will have to be answered.
Maybe it would be better to shift gears and ask: when DinoMorph is applied to extant animals, does it accurately predict the neutral pose and ROM?
It might be better to ask that question, but there are no published answers. From the first DinoMorph paper, where the method is justified (Stevens and Parrish 1999: p. 798):
Our manipulation of muscle and ligament preparations of extant bird necks indicated that synovial capsules constrain movement such that paired pre- and postzygapophyses could only be displaced to the point where the margin of one facet reaches roughly the midpoint of the other facet, at which point the capsule is stretched taut (20). In other words, one facet could slip upon the other until their overlap was reduced to about 50%. In vivo, muscles, ligaments, and fascia may have further limited movement (20); thus, the digital manipulations reported here represent a “best case” scenario for neck mobility.
The reference supporting all this is number 20 (remember how much I like numbered references?), and here’s the full text (Stevens and Parrish 1999: p. 800):
20. J. M. Parrish and K. Stevens, unpublished data.
Those data are still unpublished. But at least one of the basic assumptions–the 50% zyg overlap bit–is contradicted by Stevens and Parrish (2005b: p. 191 [not to mention by Taylor et al. 2009]).
It’s been a decade. There have been three subsequent papers on this stuff (Stevens 2002, Stevens and Parrish 2005a, b). The DinoMorph results have been the foundation for sauropod depictions in the biggest dinosaur documentary ever made and for an exhibit at the biggest natural history museum in the world. And we have no idea if the method is accurate, because the supporting data have never been published.
Sadly, this is not that uncommon in paleontology, particularly when it comes to sauropods, and especially when it comes to necks. Someone comes up with a totally new method, and right out of the gate it gets applied to a thorny paleontological problem, before it’s been demonstrated to work on extant animals. It’s exciting, it’s seductive, and it’s hard to screw up, because when you apply an unproven method to an unsolved problem, it’s impossible to get the wrong answer. In fact, the results are “not even wrong“; it’s impossible to get an answer of any value whatsoever, because there is no way of judging its correctness.
In contrast, the work of Christian and Dzemski (2007) on neck posture in Brachiosaurus warrants serious consideration, not because of the particular answer they got for Brachiosaurus, but because they got the right answers when they applied their method to extant long-necked animals (ostriches and camels; Dzemski and Christian 2007). Don Henderson and Ryosuke Motani, among others, have also been religious about ground-truthing their methods on extant animals before applying them to fossil taxa. That shouldn’t be exceptional. It should be expected. It should be the minimum requirement for being included in the discussion.
Conclusion: Let’s move forward
I can’t accuse the makers of Walking With Dinosaurs or the designers of Dinosaurs: Ancient Fossils, New Discoveries of drinking the DinoMorph Kool-Aid. I don’t know that it is Kool-Aid. It might be fine wine. There’s red stuff in the cup, but no one has tasted it.
If you get nothing else from this post, please understand that I’m not saying the results of DinoMorph are either good or bad. I’m saying that there is currently no objective way of knowing. I want DinoMorph to work, but I want a DinoMorph made rigorous by the publication of supporting data from extant animals demonstrating its accuracy, and ranges of error demonstrating its precision.
If someone has a novel method they want to apply to dinosaurs or any other extinct animal, the burden of proof is on them to show that the method works. And if that evidence is not forthcoming, you–reviewers, editors, readers, science journalists, museum exhibit designers, documentary producers, netizens, laypeople–have the right to ask for it. And until you get that supporting evidence, you don’t have to take the results of the method seriously. Asking “how do you know that?” is the basis of science; it ought to be reflexive.
In the immortal words of Tom Holtz, “Sorry if that makes some people feel bad, but I’m not in the ‘make people feel good business'; I’m a scientist.”
- Christian, A. and Dzemski, G. 2007. Reconstruction of the cervical skeleton posture of Brachiosaurus brancai Janensch, 1914 by an analysis of the intervertebral stress along the neck and a comparison with the results of different approaches. Fossil Record 10: 38–49. (subscription required)
- Dzemski, G., and Christian, A. (2007) Flexibility along the neck of the ostrich (Struthio camelus) and consequences for the reconstruction of dinosaurs with extreme neck length. Journal of Morphology 268(8):701-714. (subscription required)
- Graur, D., and Martin, W. 2004. Reading the entrails of chickens: molecular timescales of evolution and the illusion of precision. Trends in Genetics 20:80-86.
- Stevens, K.A. 2002. DinoMorph: Parametric modeling of skeletal structures. Senckenbergiana Lethaea 82(1): 23-34.
- Stevens, K.A. and Parrish, J.M. 1999. Neck posture and feeding habits of two Jurassic sauropod dinosaurs. Science 284: 798–800. (subscription required)
- Stevens, K.A. and Parrish, J.M. 2005a. Neck posture, dentition, and feeding strategies in Jurassic sauropod dinosaurs. In: V. Tidwell and K. Carpenter (eds.), Thunder−Lizards: The Sauropodomorph Dinosaurs, 212–232. Indiana University Press, Bloomington, Indiana.
- Stevens, K.A. and Parrish, J.M. 2005b. Digital reconstructions of sauropod dinosaurs and implications for feeding. In: K.A. Curry Rogers and J.A. Wilson (eds.), The Sauropods: Evolution and Paleobiology, 178–200. University of California Press, Berkeley, California.
- Taylor, M.P., Wedel, M.J. and Naish, D. 2009. Head and neck posture in sauropod dinosaurs inferred from extant animals. Acta Palaeontologica Polonica 54(2): 213-220.