November 6, 2013
Last time, we looked at how including intervertebral cartilage changes the neutral pose of a neck – or, more specifically, of the sequence of cervical vertebrae. The key finding (which is inexplicably missing from the actual paper, Taylor and Wedel 2013c) is that adding cartilage of thickness x between vertebrae whose zygapophyses are height y above the mid-height of the centra elevates the joint’s neutral posture by x/y radians.
But how thick was the intervertebral cartilage in sauropods?
Determining the ONP of a sauropod’s cervical vertebral column given only its bones requires is necessarily speculative since the cartilage, and thus the intervertebral spacing, is unknown.
Part of the our goal in our own PLOS collection paper (Taylor and Wedel 2013c) was to take some very tentative first steps towards estimating the cartilage thickness. To do this, we used two approaches. First, we looked at CT scans of articulated vertebrae; and second, we measured the cartilage thickness in a selection of extant animals and thought about what we could extrapolate.
Since the CT scans were Matt’s domain, I’m going to pass over those for now, in the hope that he’ll blog about that part of the paper. Here, I want to look at the extant-animal survey.
The first thing to say is that our survey is inadequate in many ways. We worked with the specimens we could get hold of, in the state we had them. This means that:
- we have a very arbitrary selection of different animals,
- they are at different ontogenetic stages, and
- their cartilage thickness was measured by a variety of methods.
Our goal was not at all to reach anything like a definitive answer, but just to get the question properly asked, and so hopefully to catalyse much a more detailed survey.
With that proviso out of the way, here are our main results (from Table 4 of the paper, though here I have removed the sauropod CT-scan rows since we’ll be writing about those separately).
|Turkey||4.56%||This study||Difference in measurements of intact neck and articulated sequence of cleaned, degreased and dried vertebrae.|
|Ostrich||6.30%||Cobley et al. (2013)||Difference in measurements of individual vertebrae with and without cartilage.|
|Rhea||2.59%||This study||Measurement of in situ cartilage in bisected neck.|
|Alligator||14.90%||This study||Measurement of in situ cartilage from photograph of cross section.|
|Horse||6.90%||This study||Measurement of in situ cartilage from photograph of cross section.|
|Camel||13.00%||This study||Crude measurement from condyle margin to cotyle lip of lateral-view X-ray. This is an interim measurement, which we hope to improve on when we obtain better images.|
|Dog||17.00%||This study||Measurement of intervertebral gaps in lateral-view X-ray, uncorrected for likely concavity of cotyles.|
|Giraffe||24.00%||This study||Difference in measurement of intact neck and closely articulated sequence of cleaned vertebrae. Young juvenile specimen.|
|Muraenosaurus||14.00%||Evans (1993)||Measurement of in situ cartilage in fossils.|
|Cryptoclidus||20.00%||Evans (1993)||Measurement of in situ cartilage in fossils.|
We’ve expressed the measurements as a ratio between cartilage thickness and the length of the bone itself — that is, cartilage/bone. Another way to think of this is that the percentage is a correction factor which you need to add onto bone length to get whole-segment length. Note that this is not the same ratio as the proportion of total segment length that consists of cartilage: that would be (cartilage thickness + bone length) / bone length.
(We also tossed in some measurements of plesiosaur neck cartilage that Mark Evans made way back when. Get that thing properly published, Mark!)
Even this small survey throws up some interesting points.
First, there is a huge range of proportional cartilage thicknesses: almost an order of magnitude from the 2.59% of the Rhea up to the 24% of the juvenile giraffe — or, even if you discard that because of its ontogenetic stage, up to 17% for the dog. And note that the 17% for the dog is probably an under-estimate, since we were working from an X-ray that doesn’t show the concavity of the vertebral cotyles.
(Two reviewers expressed scepticism that this is the usual condition for dogs, but this X-ray is consistent with those of other dogs illustrated in the veterinary literature.)
The second thing to note is that the cartilage measurements for birds (average 4.5%) are are much lower than those of crocodilians (14.9%) or mammals (15.2%). What does this mean? Among these groups, sauropods are most closely related to birds; but birds and crocs form the extant phylogenetic bracket, so we can’t tell from phylogeny alone whether to expect them to more closely approach the avian or crocodilian condition. Furthermore, in being opisthocoelous (condyle in front, cotyle at the back) sauropod cervicals most closely resemble those of mammals in gross structure — and they have the thickest cartilage of all.
The third thing to note is that there is considerable variation within groups. Although the cartilage is proportionally thin for all three birds, it’s more than twice as thick in the ostrich as in the rhea (although some of this could be due to the different measurement methods used for these two birds). More interestingly, among mammals the cartilage is twice as thick in camels as in horses. In the horse, the condyles are deeply inserted into the cotyles of the preceding vertebrae; but in camels, they don’t reach even the lip of the cotyle. This should worry us, as horse and camel cervicals are grossly similar, and no osteological correlates have been identified that would allow us to determine from the bones alone how very different the cartilage is between these two mammals. So it seems possible that there were similarly dramatic differences in the neck-cartilage thickness of different sauropods.
Note: I said that no osteological correlates have been identified. That doesn’t mean they don’t exist. One thing I would love to see is a serious attempt to analyse cartilage thickness across a broad range of mammals, and to examine the corresponding dry bones to see whether in fact there are correlates that could be informative in this respect. One lesson that Matt and I have learned over and over again is that there’s often plenty of data in places that are out in the open, but where no-one’s thought to look.
Next time: more on searching for osteological correlates of cartilage. Then, measurements of sauropod-neck cartilage from CT scans, and likely implications for cartilage thickness in life.
- Cobley, Matthew J., Emily J. Rayfield, and Paul M. Barrett. 2013. Inter-vertebral flexibility of the ostrich neck: implications for estimating sauropod neck flexibility. PLOS ONE 8(8):e72187. 10 pages. doi:10.1371/journal.pone.0072187 [PDF]
- Evans, Mark. 1993. An investigation into the neck flexibility of two plesiosauroid plesiosaurs: Cryptoclidus eurymerus and Muraenosaurus leedsii. University College London: MSc thesis. London.
- Stevens, Kent A. 2013. The articulation of sauropod necks: methodology and mythology. PLOS ONE 8(10): e78572. 27 pages. doi:10.1371/journal.pone.0078572 [PDF]
- Taylor, Michael P., and Matthew J. Wedel. 2013c. The effect of intervertebral cartilage on neutral posture and range of motion in the necks of sauropod dinosaurs. PLOS ONE 8(10): e78214. 17 pages. doi:10.1371/journal.pone.0078214 [PDF]
October 4, 2013
For a palaeontology blog, we don’t talk a lot about geology. Time to fix that, courtesy of my middle son Matthew, currently 13 years old, who made this helpful guide to the rock cycle as Geology homework.
September 17, 2013
I liked it, but I thought it could use some color, so I hacked a crude version in GIMP and sent it to Mark with a, “Hey, please put this on a t-shirt so I can throw money at you” plea. Lo and behold, he did just that.
You can get your own from Mark’s Zazzle store. And apparently he will have more sauropod-themed merch coming soon.
September 6, 2013
We’re just back from SVPCA 2013 in Edinburgh. The first part of the meeting was held at the Royal Society of Edinburgh, but on Friday we moved to the National Museums Scotland. Which is awesome. And free to the public. The design process for the museum seems to have been, “Okay, let’s get one of, oh, every interesting thing in the world, and put it right here.” We have tons more photos of amazing things from the museum, and maybe we’ll get around to posting them sooner or later, but today I have other things to do.
Like make fun of Mike. And talk about vomiting dinosaurs.
This groovy stuffed fulmar, Fulmarus glacialis, is shown in the act of puking, which it does to dissuade predators. And probably everyone else. I am reliably informed by Darren that this is unrealistic fulmar vomit, and that the real thing is more of a thin stream, like the world’s nastiest water gun, which can be directed with considerable accuracy. Note to self: don’t piss off the fulmars.
Last year cemented “drawing goofy sauropods down at the pub” as a regular SVPCA Thing. So one night I was out with Mike and Darren and paleoartist Bob Nicholls, who is famous around these parts as the creator of the Greatest. Paleoart. Ever. I did a goofy sketch in my notebook illustrating the “defensive vomit” hypothesis, which Brian Engh and I cooked up during this alligator dissection. More on that another time, maybe. Anyway, after bashing out a fairly pathetic sauropod-puking-on-theropod scene, I passed the notebook to Bob and said, “Make this not suck”. Which he did. (Seriously, if you could see my original scrawl, you’d be the one throwing up.)
So now I have an original Bob Nicholls sketch–heck, the world’s first Wedel-Nicholls artist collaboration!–in my notebook, of one of evolution’s most majestic successes responding appropriately to a vulgar, overstudied theropod. Bob drew it right in front of me and I got to drink good beer while I watched him work.
And that, more or less, is why I attend SVPCA.
I couldn’t sign off without giving you another version of Giant Irish Mike, with the background cropped out so he can be dropped right into posters, slide shows, and other works of science and art. I really, really hope that he turns up in conference talks and other presentations in the months and years to come. If so, send us a photo documenting his miraculous apparition and we’ll show it to the world.
Another nice display from the Museum of Osteology in Oklahoma City (previous MoO posts here and here). Check out the really gnarly ones that are indeed growing right through the bones of the face. That must have sucked.
We’ve covered rodent teeth here a few times before (one, two)–more than is probably right, for a blog ostensibly about sauropod vertebrae. Sherlock Holmes said, “Life is a great chain, the nature of which can be determined by the discovery of a single link.” I’d amend that to, “Life is a great tree, the inherent fascination of which flows through every tiny twig.”
Back when we started SV-POW!, Mike predicted that the technical niche blog was the wave of the future. That prediction does seem to be coming true, albeit more slowly than I thought it would. Nevertheless, if you are susceptible to the inherent fascination of rodent teeth, get yourself over to Ian Corfe’s Tetrapod Teeth & Tales for more geeky goodness.
Now, in a move that will possibly enrage one segment of the audience but hopefully delight another, I am going to forge even further away from the ostensible raison d’être of the blog and talk about monsters. Specifically Cthulhu–in my experience, in the Venn diagram of life, the “interested in paleo” and “interested in Lovecraft” circles overlap almost entirely. Over at my everything-except-paleontology-and-astronomy blog, I’ve been thinking about Lovecraftiana and wrestling with what a Cthulhu idol, such as those described in Lovecraft’s stories, ought to look like. If you’d like to contribute, get on over there and leave a comment. If you send* me a picture (drawing, painting, 3D render, photo of sculpture, whatever) or leave a link, I’ll include it in an upcoming post. Cthulhu fhtagn!
* Send to firstname.lastname@example.org, please include Cthulhu in the subject line.
June 30, 2013
Well, I’m back. Been on the road a lot–to Flagstaff for a few days around Memorial Day, and in Oklahoma to visit family in the first half of June. Now I’m busy with the summer anatomy course, but I finally found time to post some pictures.
One of my favorite museums in the world is the Museum of Osteology in Oklahoma City. It hits all the right notes for me: just shedloads of stuff on display, mounts you can walk all around and even touch (all they ask is that you don’t climb on them), and nary an interactive gizmo in sight. Plus a gift shop at the end where I could easily spend an hour (and several thousand dollars, if I had that much disposable dough and someplace to put all the loot). This was my second visit, but I never got around to posting the photos from my last visit, so maybe I can make up for that this summer. This post just has some highlights–I’ll try to get more photos up before another month goes by.
One of my favorite things in the museum is this awesome and appropriate triple display of the three-banded armadillo.
And old friend, from a new perspective.
In my experience, in the Great Plains states it is a rare museum indeed that does not have a two-headed calf. Not just natural history museums, either–historical museums and roadside attractions usually have at least one. The first I ever encountered was at the Dalton Gang Hideout in Meade, Kansas–maybe someone knows if it is still there? Even as a kid, I understood that the link between bovine developmental anomalies and Old West outlaws was pretty tenuous–basically, both crop up in Kansas–but I didn’t mind then and I don’t mind now. IMHO, finding two-headed calves on display in unexpected places only reinforces the concept of museums as cabinets of wonder.
Of course, it is entirely appropriate to find two-headed calves in an osteology museum, and the Museum of Osteology has more specimens than I’ve ever seen in one place.
The herp case is rad: the anaconda in the middle is a 14-footer, and the king cobra at lower right is 13’7″. And check out the super-fat Gaboon viper below the anaconda. If you’re wondering about turtles and crocs, they’re in the next case over.
As anyone who followed Darren’s multi-part series on matamatas (1, 2, 3, 4, 5) knows, they are fabulously weird. As I conceive it, there are two kinds of turtles: matamatas, and “regular-ass turtles”, the latter being the paraphyletic group that includes all non-matamata turtles.
My favorite mounts in the Museum of Osteology are the smallest: a pair of impossibly tiny ruby-throated hummingbirds.
I spend a lot of time with vertebrate bodies and skeletons, both taking them apart and putting them back together, and I am not exaggerating when I say that these are the most astonishing skeletal mounts I have ever seen. Unfortunately there aren’t any external indicators of scale with these skeletons, and perspective effects would defeat any attempt to put a scale bar up against the glass. These ruby-throated hummingbirds are slightly longer-billed than the Anna’s hummingbird mentioned in this post, but even so the skulls are probably no more than 30mm long. I recently helped London clean up a rat skull (yet another thing I need to blog about), and that skull was about as big as one of these skeletons minus the bill.
That’s all for now. If you’re ever in Oklahoma City, go check out the Museum of Osteology. I recommend it to anyone who is interested in bones, anatomy, animals, nature, or even, like, things.
May 1, 2013
September 26, 2012
Today sees the publication, on arXiv (more on that choice in a separate post), of Mike and Matt’s new paper on sauropod neck anatomy. In this paper, we try to figure out why it is that sauropods evolved necks six times longer than that of the world-record giraffe — as shown in Figure 3 from the paper (with a small version of Figure 1 included as a cameo to the same scale):
This paper started life as a late-night discussion over a couple of beers, while Matt was over in England for SVPCA back in (I think) 2008. It was originally going to be a short note in PaleoBios, just noting some of the oddities of sauropod cervical architecture — such as the way that cervical ribs, ventral to the centra, elongate posteriorly but their dorsal counterparts the epipophyses do not.
As so often, the tale grew in the telling, so that a paper we’d initially imagined as a two-or-three-page note became Chapter 5 of my dissertation under the sober title of “Vertebral morphology and the evolution of long necks in sauropod dinosaurs”, weighing in at 41 1.5-spaced pages. By now the manuscript had metastatised into a comparison between the necks of sauropods and other animals and an analysis of the factors that enabled sauropods to achieve so much more than mammals, birds, other theropods and pterosaurs.
(At this point we had one of our less satisfactory reviewing experiences. We sent the manuscript to a respected journal, where it wasn’t even sent out to reviewers until more than a month had passed. We then had to repeatedly prod the editor before anything else happened. Eventually, two reviews came back: one of them careful and detailed; but the other, which we’d waited five months for, dismissed our 53-page manuscript in 108 words. So two words per page, or about 2/3 of a word per day of review time. But let’s not dwell on that.)
This work made its next appearance as my talk at SVPCA 2010 in Cambridge, under the title Why giraffes have such short necks. For the talk, I radically restructured the material into a form that had a stronger narrative – a process that involved a lot of back and forth with Matt, dry-running the talk, and workshopping the order in which ideas were presented. The talk seemed to go down well, and we liked the new structure so much more than the old that we reworked the manuscript into a form that more closely resembled the talk.
That’s the version of the manuscript that we perfected in New York when we should have been at all-you-can-eat sushi places. It’s the version that we submitted on the train from New York to New Haven as we went to visit the collections of the Yale Peabody Museum. And it’s the version that was cursorily rejected from mid-to-low ranked palaeo journal because a reviewer said “The manuscript reads as a long “story” instead of a scientific manuscript” — which was of course precisely what we’d intended.
Needless to say, it was deeply disheartening to have had what we were convinced was a good paper rejected twice from journals, at a cost of three years’ delay, on the basis of these reviews. One option would have been to put the manuscript back into the conventional “scientific paper” straitjacket for the second journal’s benefit. But no. We were not going to invest more work to make the paper less good. We decided to keep it in its current, more readable, form and to find a journal that likes it on that basis.
At the moment, the plan is to send it to PeerJ when that opens to submissions. (Both Matt and I are already members.) But that three-years-and-rolling delay really rankles, and we both felt that it wasn’t serving science to keep the paper locked up until it finally makes it into a journal — hence the deposition in arXiv which we plan to talk about more next time.
In the paper, we review seven characteristics of sauropod anatomy that facilitated the evolution of long necks: absolutely large body size; quadrupedal stance; proportionally small, light head; large number of cervical vertebrae; elongation of cervical vertebrae; air-sac system; and vertebral pneumaticity. And we show that giraffes have only two of these seven features. (Ostriches do the next best, with five, but they are defeated by their feeble absolute size.)
The paper incorporates some material from SV-POW! posts, including Sauropods were corn-on-the-cob, not shish kebabs. In fact, come to think of it, we should have cited that post as a source. Oh well. We do cite one SV-POW! post: Darren’s Invading the postzyg, which at the time of writing is the only published-in-any-sense source for pneumaticity invading cervical postzygapogyses from the medial surface.
As for the non-extended epipophyses that kicked the whole project off: we did illustrate how they could look, and discussed why they would seem to make mechanical sense:
But we found and explained some good reasons why this apparently appealing arrangement would not work. You’ll need to read the paper for details.
Sadly, we were not able to include this slide from the talk illustrating the consequences:
Anyway, go and read the paper! It’s freely available, of course, like all arXiv depositions, and in particular uses the permissive Creative Commons Attribution (CC BY) licence. We have assembled related information over on this page, including full-resolution versions of all the figures.
In the fields of maths, physics and computer science, where deposition in arXiv is ubiquitous, standard practice is to go right ahead and cite works in arXiv as soon as they’re available, rather than waiting for them to appear in journals. We will be happy for the same to happen with our paper: if it contains information that’s of value to you, then feel free to cite the arXiv version.
September 25, 2012
Another extraordinary specimen from the wonderful Oxford University Museum of Natural History: the skeleton of a goliath frog Conraua goliath, the largest extant anuran, which comfortably exceeds 30 cm and 3 kg in life:
As noted by sometime SV-POW!sketeer Darren Naish over on Tetrapod Zoology, frogs have stupidly weird skeletons — surely the most derived of any tetrapod, despite their lowly, early diverging “amphibian” status. Rather than describe all the oddities myself, I’ll just quote Darren’s article:
Anurans have (at most) nine presacral vertebrae, and some have as few as five; ribs are either highly reduced or absent; the radius and ulna are fused (forming the radioulna); the bones of the pectoral girdle are highly reduced and complimented by an assortment of new weird bits; the pelvis consists of a rod-like central unit (the urostyle) surrounded by two super-long, shaft-like ilia; and in their (generally) elongate hindlimbs, the tibia and fibula are fused (forming the tibiofibula) while the ankle bones are elongated to form a long ‘extra’ limb segment.
That’s a pretty astonishing list; and, sure enough, frog skeletons weird me out every time I see them. (Of all the dead animals I’d like to get hold of in decent condition, to extract the bones from, frogs miss the top of the list only to bats, crocs and turtles. And maybe raptors.)
This particular species of frog has another skeletal oddity that caught my eye:
As you can see, the humerus is perforated: there is a distinct foramen running down it just behind the anterior edge. Is the anterior bar a partially detached deltopectoral crest? Or is it a completely novel ossification that has become partially fused to the humerus?
For what it’s worth, this feature doesn’t seem to be consistently present in goliath frogs. A bit of googling shows that it’s present in this skeleton, but not in this one from Bone Clones. The humerus of the latter does have a distinctly protruding deltopectoral crest, but it lacks the perforation. So I guess that is evidence against the Novel Ossification hypothesis.
Does anyone know more about this odd feature? Does it develop through ontogeny? Is it found in other frogs? What is its mechanical significance?
June 23, 2012
Here’s a cool skeleton of the South American pleurodire Podocnemis in the Yale Peabody Museum.
What’s that you’re hiding in your neck, Podocnemis?
Laminae! Here’s a closeup:
The laminae run from the transverse processes to the prezygapophyses and the centrum, which I reckon makes them analogues of the PRDLs and ACDLs of sauropods.
As long as I’m posting on Peabody turtles, here’s Archelon. It’s not bad, if you’re into that sort of thing. Which Mike clearly ain’t, but for a good reason, which will be revealed soon.