Just a quick photo-post today. A couple of months ago, walking around the fields near our house, I found a broad shallow pit with a lot of a sheep skeletal elements in it. I took my youngest son out on an expedition, and we rescued the good material. I’ve cleaned up the first two (of three) skulls. Here is the smaller of the two — which is also more complete, and the big one has lost its nasals.

IMG_1707-oblique

Click through for glorious high-resolution (4000 x 3000, and not a pixel wasted).

I took a nice set of orthogonal-view photos of this skull. When I have time, I will clean them up and composite them as I did with my pig-skull, which I’m sure you all remember:

pig-skull-white

(Well … I call it my pig skull, but it’s not mine any longer. I donated it as the prize for winning the TetZooCon quiz, and it is now the proud possession of Kelvin Britton. But I have another one, so that’s all right.)

A couple of times now, I’ve pitched in an abstract for a Masters project looking at neck cartilage, hoping someone at Bristol will work on it with me co-supervising, but so far no-one’s bitten. Here’s how I’ve been describing it:

Understanding posture and motion in the necks of sauropods: the crucial role of cartilage in intervertebral joints

The sauropod dinosaurs were an order of magnitude bigger than any other terrestrial animal. Much sauropod research has concentrated on their long necks, which were crucial to their success (e.g. Sander et al. 2010). One approach to understanding neck function tries to determine neutral posture and range of motion by modelling the cervical vertebrae as a mechanical system (e.g. Stevens and Parrish 1999).

The raw material of such studies is fossilised vertebrae, but these are problematic for several reasons. The invariable incompleteness and distortion of sauropod neck fossils causes fundamental difficulties; but even given perfect fossils, the lack of preserved cartilage means that the bones are not shaped or sized as they were in life.

Ignoring cartilage has dramatic consequences for neutral posture, range of motion and even length of necks: pilot studies (Cobley 2011, Taylor 2011) found that intact bird necks are 8–12% longer than articulated sequences of their dry bones, and that figure is as high as 24% for a juvenile giraffe neck. A turkey neck postzygapophysis was 26% longer when cartilage was included than after being stripped down to naked bone.

We do not yet know how much articular cartilage sauropods had in their necks, nor even what kind of intervertebral joints they had: crocodilians have fibrocartilaginous discs like those of mammals, while birds have synovial joints, so the extant phylogenetic bracket is uninformative.

The project will involve dissection and measurement of bird and crocodilian necks, documenting the extent and shape of articular cartilage, identifying osteological correlates of fibrocartilaginous and synovial joints, and applying this data to sauropods to determine the nature of their neck joints and length of their necks, to reconstruct the lost cartilage, and to determine its effect on neutral pose and range of motion.

Following completion, we anticipate publication of the project.

References

Cobley, Matthew J. 2011. The flexibility and musculature of the ostrich neck: implications for the feeding ecology and reconstruction of the Sauropoda (Dinosauria: Saurischia). MSc Thesis, Department of Earth Sciences, University of Bristol. vi+64 pages.

Sander, P. Martin, Andreas Christian, Marcus Clauss, Regina Fechner, Carole T. Gee, Eva-Maria Griebeler, Hanns-Christian Gunga, Jürgen Hummel, Heinrich Mallison, Steven F. Perry, Holger Preuschoft, Oliver W. M. Rauhut, Kristian Remes, Thomas Tütken, Oliver Wings and Ulrich Witzel. 2010. Biology of the sauropod dinosaurs: the evolution of gigantism. Biological Reviews 86:117–155. doi:10.1111/j.1469-185X.2010.00137.x

Stevens, Kent A., and J. Michael Parrish. 1999. Neck Posture and Feeding Habits of Two Jurassic Sauropod Dinosaurs. Science 284:798–800. doi:10.1126/science.284.5415.798

Taylor, Michael P., and Mathew J. Wedel. 2011. Sauropod necks: how much do we really know?. p. 20 in Richard Forrest (ed.), Abstracts of Presentations, 59th Annual Symposium of Vertebrae Palaeontology and Comparative Anatomy, Lyme Regis, Dorset, UK, September 12th–17th 2011. 37 pp. http://www.miketaylor.org.uk/dino/pubs/svpca2011/TaylorWedel2011-what-do-we-really-know.ppt

(Obviously some part of this have since been covered by my and Matt’s first cartilage paper, but plenty has not.)

I now think there are two reasons no-one’s taken up this project: first, because I wrote it as very focussed only on the question of what type of joint was present, whereas there are plenty of related issues to be investigated along the way; and second, because I wrote it as a quest to discover a specific treasure (an osteological correlate), with the implication that if there’s no treasure to be found then the project will have been a failure.

But I do think there is still plenty of important work to be done in this area, and that there’s lots of important information to be got out of comparative dissection of extant critters.

If anyone out there fancies working in this area, I’d be delighted. I’d also be happy to offer whatever advice and help I could.

Update (18 October 2014)

Somehow I’d forgotten, when I wrote this post, that I’d previously written a more detailed post about the discs-in-sauropod-necks problem. If you’re interested in the problem, you should read that.

 

Internal Iliac Arteries - MJW 2011

Here’s a thing I put together to help my students understand the many branches of the internal iliac artery in humans. In the image above, we’re looking in superomedial view into the right half of the sacrum and pelvis. Bones are white, ligaments blue, the piriformis muscle sort of meat-colored, and arteries red (for a tour of the pelvis identifying all of this stuff, see my pelvic foramina slideshow). At the top is a big inverted Y-shape: the common iliac arteries branching from the abdominal aorta, which continues on, much reduced, as the median sacral artery. The right common iliac artery is shown bifurcating into the external iliac artery, which continues on out of the pelvis to become the femoral artery, and the internal iliac artery, source of much fear and doubt.

The first thing to understand is that any particular branching pattern of the internal iliac arteries, whether in an anatomical altas, a lecture, revealed in a dream, or even in your own body, will probably have no bearing whatsoever on the branching pattern in the next person you encounter, alive or dead. Furthermore, the variation between right and left in a single person can be as great as that among different people. The branches to pelvic viscera are particularly fiendish; they sometimes travel far into the pelvis as a common trunk and then “starburst” near their target organs, making identification almost impossible. Do not waste your time trying to memorize any particular branching sequence. Instead, concentrate on matching the arteries to their targets; you will discover the identities of the branches by seeing where they are going, not the order in which they branch.

There are typically 10 named branches of the internal iliac artery. Authorities quibble on the details, as we’ll see in a moment, but if you know these 10, you’ll be fine for almost any conceivable purpose. A simple scheme of my own devising for remembering them is 2-4-4:

TWO to the back body wall:

  1. iliolumbar A—may arise from external or common iliac AA; sometimes double
  2. lateral sacral A—note branches to anterior sacral foramina and anastomoses with median sacral A

FOUR leaving the pelvis entirely:

  1. obturator A—often arises from the external iliac A instead, exits pelvis through obturator canal
  2. superior gluteal A—exits pelvis through suprapiriform foramen
  3. inferior gluteal A—exits pelvis through infrapiriform foramen, with internal pudendal A
  4. internal pudendal A—exits pelvis through infrapiriform foramen, with inferior gluteal A

FOUR to pelvic viscera:

  1. superior vesical A—usually the dominant artery of the anterior trunk, this is the patent part of the obliterated umbilical artery, which survives as the medial umbilical ligament
  2. inferior vesical A (males) / vaginal A (females)—may branch off uterine A (females) or superior vesical A (both)
  3. uterine A (females)—major artery to uterus, approaches laterally within the broad ligament
    A to ductus deferens (males)—extremely small and difficult to trace
  4. middle rectal A—usually the most inferior branch of the entire internal iliac tree (at least inside the pelvis)

My way to explain those last four is to extend my index finger and say, “Everybody has to pee, so up front we have superior vesical.” Then extend my pinky and say, “And everyone has to poop, so in back we have middle rectal.” Then extend digits three and four and explain that the identity of the middle two arteries varies between the sexes (but that the inferior vesical artery of males and the vaginal artery of females are basically the same vessel).

There is a LOT of variation in the descriptions of the internal iliac artery branches among different sources — almost as much variation as there is in the arteries themselves.

  • ​The Thieme Atlas of Anatomy, 2nd Ed (Gilroy et al. 2009), Table 19.1 on p. 254, includes the inferior vesical artery for both sexes. The artery to ductus deferens is listed as a branch of the superior vesical artery, and the uterine and vaginal arteries are listed separately, bringing the total for females to 11.
  • Clinically Oriented Anatomy, 7th Ed (Moore et al. 2013), Table 3.4 and pp. 350-355, lists the 10 branches I went through above. Moore et al. explicitly say that the vaginal artery is the female homolog of the inferior vesical artery (p. 351).
  • Gray’s Anatomy, 40th Ed (Standring et al. 2008), pp. 1085-1089, splits the difference. The artery to ductus deferens is not listed; instead, the ductus deferens is said to be supplied by the inferior vesical A (in contrast to Thieme, which has it is supplied by the superior vesical A). Both the vaginal and inferior vesical arteries are listed, but the vaginal artery is said to frequently replace the inferior vesical artery.

The upshot is that pretty much all of these sources agree on how the blood is getting distributed, there are just some minor differences over what we call certain vessels. I have never personally seen a dissection detailed enough to allow an interior vesical artery to be recognized separately from the vaginal artery — the vagina lies so close behind the bladder that whatever you call the artery that runs lateral to them, it could easily be supplying both structures, and probably does. As far as I’m concerned, the inferior vesical artery in males and the vaginal artery in females are the same artery, in that they both supply the inferior portion of the bladder. I think it’s just a historical hiccup that we call them by different names, possibly perpetrated by smelly, lonely, vagina-obsessed men of centuries past.

A final note, added in revision: some sources refer to two trunks or divisions of the internal iliac artery: a posterior trunk that gives rise to the iliolumbar, lateral sacral, and superior gluteal arteries, and an anterior trunk that gives rise to everything else. If that’s what your professor tells you, smile and nod and keep your heretical thoughts to yourself. Personally, I regard the notion of trunks of the internal iliac artery alongside phlogiston, luminiferous aether, and snorkeling sauropods, as romantic nonsense at best. I have seen an obturator artery arise from a superior gluteal artery and a pudendal artery arise from a superior vesical artery. In a world where variants like those can and do turn up frequently, the stability and reason implied by regular trunks is illusory.

References

  • Gilroy, A., MacPherson, B., and Ross, L. (eds.) 2009. Atlas of Anatomy, 2nd ed. Thieme, Stuttgart.
  • Moore, K.L., Dalley, A.F., and Agur, A.M. 2013. Clincially Oriented Anatomy, 7th ed. Lippincott Williams & Wilkins, Philadelphia.
  • Standring, S. 2008. Gray’s Anatomy, 40 ed. Churchill Livingstone, London.
Cervical rib cross-sections from Mamenchisaurus Giraffatitan and Diplodocus Klein et al 2012 fig 1

Klein et al. (2012: fig. 1)

We have good descriptions of the proximal parts of the cervical ribs for lots of sauropods. We also have histological cross-sections of a few, mostly thanks to the work of Nicole Klein and colleagues (Klein et al. 2012, Preuschoft and Klein 2013), although histological cross-sections of ribs were also figured as long ago as 1999, by Dalla Vecchia (1999: figs. 29 and 30), and as recently as this month, by Lacovara et al. (2014: supplementary figure 4).

What we have very, very few of is series of cross-sections that show how the cr0ss-section of a cervical rib changes along its length. There may be more out there (and if I have forgotten any, please remind me!), but at the moment I can only think of three such figures: two in Janensch (1950: figs. 83 and 85), both on Giraffatitan, and one in Klein et al. (2012: fig. 1), with cross-sections from Mamenchisaurus, Giraffatitan, and Diplodocus (shown at the top of the post).

Sauroposeidon cervical rib cross-sections v3

 

Rarer still are images that show cross-sections of overlapped cervical ribs, stacked in situ. You could use the information in Janensch (1950: figs. 83 and 85) to generate the stacked cross-sections, but you wouldn’t know the spacing between the ribs as they were in the ground. I think the image just above, of the cervical rib bundles in the Sauroposeidon holotype, OMNH 53062, may be the first of its kind–again, if you know of any others, please let me know. I took the notes for this figure back in 2004, sitting down with the holotype and some digital calipers to make sure I could scale everything correctly, I just hadn’t ever put it into a presentable form until now. The first C6 section (blue V-shape) is from right at the root where the capitulum and tuberculum meet and the posterior shaft of the rib begins.

It is by now well-understood that the long cervical ribs of sauropods and other dinosaurs are ossified tendons of the long hypaxial neck muscles, specifically the longus colli ventralis and flexor colli lateralis. We argued this back in 200o on comparative anatomical grounds (Wedel et al. 2000b: pp. 378-379), and it has now been demonstrated histologically (Klein et al. 2012, Lacovara et al. 2014). The system of stacked tendons is also found in most birds. Here’s the bundle of stacked tendons in a rhea neck, only slightly fanned out:

Rhea ventral tendons stacked - full

And the same neck, with both the epaxial and hypaxial muscles more fully separated:

Rhea neck muscles fanned - full

What I’d really like is an MRI of a rhea or ostrich neck, showing the stacked tendons and their associated belts of muscle, to compare with the stacked cervical ribs of Sauroposeidon and other sauropods. Anyone know of any?

Incidentally, I think the cervical ribs and cervical rib bundles of sauropods are one line of evidence for sauropod necks having been rather slenderly-muscled. The long, multi-segment muscles like the longus colli ventralis are the outermost components of the muscular envelope that surrounds the vertebrae, as you can see in the rhea dissection photos. In sauropod specimens with articulated cervical ribs, the ribs do not deviate from one another or fan out. Rather, they lie in vertically stacked bundles that run from one capitulum-tuberculum intersection to the next. So the depth of that intersection–the “root” of the cervical rib of any given vertebra–plus the thickness of the ribs stacked underneath it, is pretty much the thickness of the muscular envelope around the neck, or at least around the ventral half. And the cervical ribs are typically pretty close to the vertebral centra–only weirdos like Apatosaurus and Erketu displace them very far ventrally (see Taylor and Wedel 2013a: fig. 7 and this post). So, thin jackets of muscle around proportionally large vertebrae–or, if you like, corn-on-the-cob rather than shish-kebabs.

As for why sauropods have long cervical ribs, Mike and I discussed some possibilities in our 2013 PeerJ paper (Taylor and Wedel 2013a), and Preuschoft and Klein addressed the issue last fall in PLOS ONE (Preuschoft and Klein 2013). My favorite hypothesis is that long tendons allow an animal to shift the bulk of the muscle–and therefore the center of gravity–toward the base of the neck, but that long unossified tendons can be distorted through stretching, which wastes muscular energy. Ossifying those long tendons is like putting bony wheelbarrow handles on each vertebra, allowing the muscles to move the vertebra from a distance without so much wasted energy, and probably with finer positional control.

That’s a nifty hypothesis in need of testing, anyway. In fact, cervical ribs and their associated muscles could stand a lot more attention on both the descriptive and analytical fronts. I know that Liguo Li has some research in the works on different conformations of hypaxial muscles, tendons, and cervical ribs in birds (you know, when she’s not describing bizarre new titanosaurs like Yongjinglong — see Li et al. 2014). If you saw Peter Dodson give their talk at SVP last fall, you probably remember some stunning images of dissected bird necks. As a famous legislator once said, we shall watch her career with great interest.

References

 



art

  




salamander

  








platyhystrix

  




another-temnospondyl

  




feathered-diplodocus


tyrannosaur


ankylosaur

  




braincase




  




diadectes

  




salamander

  




salamander-silhouette

  




gar

  




fish


shark



stamp-trex

  





lampreyhagfish

  




tsintaosaurus

I was skim-reading the Political Studies Association’s evidence submitted to RCUK’s review. I was struck by one part that perpetuates a common but completely unfounded misapprehension:

There is little enthusiasm for CC-BY [...] in the field of political studies. [...] It is clear that there is serious concern about the potential for work published under a CC-BY licence to be distorted and used inappropriately.

There may be concern, but it’s misplaced. Using CC By does not allow your work to be misrepresented. The human-readably summary of the licence clearly states, in its definition of the attribution clause: [Emphasis added]

You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.

What does this mean? It means creationists can’t take our paper on sauropod neck anatomy, change it so that we seem to be advocating Intelligent Design, and post the result as though it’s our work. Instead, the terms of the licence require that they state that changes were made, and that they do not portray us as endorsing their use.

Really, I don’t see how much clearer or simpler the CC By licence could be. It’s 108 words long. For heavens’ sake, folks, go and read it. It’s ridiculous that we have academics, who are supposed to be trained in research and rigour, expressing flagrantly incorrect opinions about a hundred-word-long document that they’ve not even read.

Gender balance at SVPCA

September 17, 2014

I’ve always thought of SVPCA as a pretty well gender-balanced conference: if not 50-50 men and women, then no more than 60-40 slanted towards men. So imagine my surprise when I ran the actual numbers.

1. Delegates. I went through the delegate list at the back of the abstracts book, counting the men and women. Those I knew, or whose name made it obvious, I noted down; the half-dozen that I couldn’t easily categorise, I have successfully stalked on the Internet. So I now know that there were 39 women and 79 men — so that women made up 33% of the delegates, almost exactly one third.

Official conference photo, SVPCA 2014, York, UK.

Official conference photo, SVPCA 2014, York, UK.

2. Presentations. There were a total of 50 presentations in the three days of SVPCA: 18 on days 1 and 3, and 14 on day 2, which had a poster session in place of the final session of four talks. I counted the presenters (which were usually, but not always, the lead authors). Here’s how the number of talks by women broke down:

Day one: 2 of 18
Day two: 8 of 14
Day three: 3 of 18

In total, this gives us 13 of 50 talks by women, or 26%.

3. Presenter:delegate ratios. Since 37 of the 79 attending men gave talks, that’s 47% of them; but only 13 of the 39 attending women gave talks, which is 33%. On other words, a man attending SVPCA was 40% more likely to give a talk than a woman.

I’m not sure what to make of all this. I was shocked when I found that only one ninth of the first day’s talks were by women. It’s a statistical oddity that women actually dominated day two, but day three was nearly as unbalanced as day one.

Since SVPCA accepts pretty much every submitted talk, the conference itself can’t be blamed for the imbalance. (At least, not unless you think the organisers should turn down talks by men just because they’re men, leaving blank spots in the program.) It seems that the imbalance more likely reflects that of the field in general. Maybe more disturbing is that the proportion of women giving talks was rather less than the proportion attending (26% vs. 33%) which suggests that perhaps women feel more confident about attending than about presenting.

It would be interesting to know how these numbers compare with SVP’s.

Follow

Get every new post delivered to your Inbox.

Join 397 other followers