No 4WD for Plateo!

In the first of my Plateosaurus posts I mentioned that my research project was planned by my thesis supervisor, Hans-Ulrich Pfretzschner. Together, we soon stumbled across a fact that became a turning point for the entire project: we were unable to articulate the lower arm of Plateosaurus so that the palm of the hand faced the ground with the fingers pointing forward (or forward/inward, forward/outward). The sole way Plateosaurus could make the palm face downward was by having the fingers pointing strictly sideways. This came as a considerable surprise to us, as it implied that our dinosaur was an obligate biped. A while later, Matt Bonnan gave a talk at the 2005 SVP in Denver (yes, Denver, CO, for you Americans out there) about research he had jointly performed with Phil Senter (Senter & Bonnan 2005). Lo and behold, they found that both Plateosaurus and the smaller, lither and relatively closely related prosauropod Massospondylus were unable to pronate their hands, both by the classic method of rotating the radius along an axis almost parallel to its length (this means that the end in the elbow rotates, and that end at the wrist “rolls around” the ulna), or any other method.

OK, scooped (unintentionally) on that one, and I must admit that Matt and Phil did a decidedly more thorough analysis, by comparing in detail to extant animals and looking at other methods for walking on all fours than simply pronating the hands, namely knuckle walking with medially directed palms. They found no indications that any of this was possible, and nor did I when I checked Plateosaurus. There remains just one little episode (rather, a series of episodes) to be told that taught me a lot about our professional training and its drawbacks and limitations, and about an easy way to overcome some of the drawbacks. It has paid off for me repeatedly. Remember that this all happened before I received the reassuring support from Phil and Matt.

…ask your doctor for advice…

During the project we had an entire skeleton of Plateosaurus, the nearly complete and well-preserved individual shown in the previous post, CT scanned at the University Hospital in Tübingen. Additionally, we had casts made of the better-preserved left arm of the second mounted skeleton, by the very capable preparator of the Tübingen Institute for Geosciences, Hans Luginsland. Hans made a set of very durable casts from plastic, and I played around with them a lot, trying out how the bones fit together. One bone pair I initially had a lot of trouble with was radius and ulna. My training in bone anatomy was (and is), I hate to admit, rather weak, but I was determined not to simply copy&paste someone’s skeleton articulation. What caused my trouble was the fact that the ulna has two distinct grooves or depressions down its length, one evidently on the inner (medial) side, one on the outer (lateral). Which was which? Both radius and ulna lack the clear articular facets seen in mammals, but still one of the two grooves seemed a very nice fit for the radius, while the other looks a bit small and weakly developed. But if I stuck the radius into the made-for-the-radius groove, then either it took a very unusual position, with its proximal end (at the elbow) on the inside of the ulna, or what looked like and was mounted as a left ulna had to be a right ulna.

I just wrote that the radius being in a medial position would be very weird – why? Birds and sauropods, and quite a bunch of other animals have their radius not in a lateral position. However, in each case the radius is in an anterior position, and there is a developmental line showing a shift from a lateral to an anterior position. Prosauropods, as either the ancestors or very close relatives to the ancestors of sauropods, should be showing the start of this shift – not a position that is “above and beyond” the requirements. However, I was pretty much alone with that assessment: museum mounts in the Staatliches Museum für Naturkunde Stuttgart (State Museum for Natural Sciences Stuttgart), the place where all the other Trossingen material went, had the radius in medial position, and Markus Moser in Munich also argued for a quadrupedal Plateosaurus. Even Huene (1926) explained how the radius would slide around the ulna during pronation. Then, there was the torrent of papers on or including Plateosaurus by Peter Galton, some of which clearly showed a fully pronated manus (e.g., Galton 1971). Gregory Paul gave my beloved Triassic monster a thorough treatment, publishing not only the by-now standard side view skeletal drawing, but anterior and posterior views at the hip, and a beautiful “life” drawing in a gallop, along with a musculature reconstruction in the same view. Paul (e.g., 1987) showed the radius laterally placed, but crossing the ulna the way it does in elephants (permanently), and humans (when pronating the hand). So who was I to question these authorities, especially given my poor knowledge of anatomy?

So I turned to a person who had no knowledge of palaeontology or dinosaurs whatsoever, but quite a lot of knowledge and expertise regarding human anatomy: my wife. Rita started her medical career in orthopaedics, but quickly changed to surgery. Although she now works for a large pharmaceutical company she has a lot of knowledge on bones and muscles. So, I handed her the casts of radius and ulna, asking her to “go ahead and articulate these”. She took one good look, and said, “radius and ulna, correct? Bunch of stuff missing – or at least that’s what it looks like to me”, indicating the articular ends. I assured her that the bones looked what dinosaur bones always look like, and did not ossify the way they do in mammals. Rita fiddled with the bones a bit, trying to figure out which end of the radius was the elbow and which the wrist, then pronounced, with a level of certainty that made the sound of her words stick in my ear to this day: “The radius should go here, in this groove!” – “OK, now please pronate the hand” I replied. To which she gave a snort and said “no way! If this radius rotates it rips the joint capsule apart!”

Game, set and match for me – but why was she so certain? Rita told me that the lateral groove had the shape of one that holds bone, while the other one looked like there should be strong muscles bunched proximally right next to it. No surprise: the finger flexors typically are located there, and they typically are bunched close to the elbow, with long tendons transferring the power to the fingers. You can see them on your own lower arm’s inner side, when you flex your fingers one by one.

I now proceeded to hand those two casts to everybody I encountered: professors, post-docs, students of medicine, palaeontology, zoology – anyone in any way connected to the field got the task of articulating them. And the quota of correct identifications was surprisingly low. I’d even say it was appalling! The vast majority of the 30 or so “experts” needed prompting on what the bones were, and only a handful was able to articulate them properly. Even those constantly looked at me for affirmative or disapproving signs, and as hard as I tried to keep a poker face, they all got what they wanted. So I can’t even say with surety that a handful quickly and with confidence was able to fit those two bones together (there are honourable exceptions, though!). This episode taught me that I should distrust anyone’s research, unless there was a solid, detailed description detailing the reasons for why results were interpreted in what way, that I should trust my own hands-on approach, and that I should always think outside my field when I was looking for expertise.

Palaeontology is an interdisciplinary science – we just tend to forget

The last point has been driven home by my wife whenever palaeopathologies or anything remotely connected to musculoskeletal anatomy and function came up, but also by other researchers’ publications. A prime example is Faux & Padian (2005), who discussed the extremely extended (backwards bent) position of many dinosaur finds. Combining a vets education and expertise with a palaeontologists’ questions they find that many show opisthotonic posture, a perimortem (during dying) or premortem (before death) effect of brain damage. This means that the extended dinosaur backs are not “broken”, telling us a lot about possible mobility in life – a result totally different from what many believed, and what I was taught when studying palaeontology. Most striking, though, is another medical publication, because of the massive influence on anything we do with dinosaurs, from the simple(?) act of measuring leg length in a complete sauropod skeleton to figuring out the range of motion of a dinosaur knee, shoulder or (most contentious) neck (for the last, see e.g., Stevens & Parrish 1999, 2005a, 2005b; Christian & Dzemski 2007; Taylor et al. 2009). I found by chance a long time ago a paper, lost my PDF copy, and only recently was able to find it again, because I suddenly remembered that it dealt with chicken cartilage, and has the word “chicken” in the title. Without the search term “chicken” I received so many hits when searching PubMed that I gave up looking, but with it the paper was among the top five hits. It is one of those papers that give us palaeontologists hard data about the Extant Phylogenetic Bracket (EPB; simply stated the two most closely related groups bracketing an extinct group) of dinosaurs, but are never noticed by the palaeo community, because they appear in a (to us) obscure medical journal.

Have you ever read the Journal of International Orthopaedics?

Well, have you? Read an article, or at least browsed the content summary on the back cover or online? I guess the honest answer will be “No, never, the journal of WHAT?” There are so many medical journals that the list of titles probably runs as long as the list of articles in palaeontology in one year; who can keep track of that even with modern search engines and email notification systems? I can’t, that’s for sure. But International Orthopaedics contains this gem:

Graf, J., Stofft, E., Freese, U. and Niethard, F.U. 1993. The ultrastructure of articular cartilage of the chicken’s knee joint. International Orthopaedics 17: 113–119.

The content is stuff I’d expect to find in any textbook on reptile anatomy, or bird anatomy – so far, however, I have not found any detailed data on bird articular cartilage in any textbook. Most make the implicit assumption that describing bone growth in detail, with a short description of the general morphology of the cartilage caps, is sufficient. However, the fundamental point for those of us not interested in tiny birds (yes, an ostrich is tiny compared to the animals I deal with), but with multi-ton archosaurs, is that the ultrastructure of the cartilage in the joint of adult birds is different from that in mammals: it has blood vessels in it! And that means that the articular cartilage can be much thicker than it is in mammals, resulting potentially in shapes and sizes of articular ends that were quite different than the preserved, fossil bone shape. Thicker cartilage results in longer limbs, too, which influences various ration often used to calculate if an animal was a biped or quadruped.

So why do we find such fundamentally important information in a journal of human medicine? Because chicken knees used to be employed as experimental models for the introduction of arthrosis in humans, and Graf et al. wanted to make sure that this approach was valid. It wasn’t, because of the significant differences between mammalian (human) and archosaur (chicken) cartilage, and the focus of the research was an application in medical research, not palaeontology, and thus the results were published in a journal we never read.

So we see that we should talk to MDs a lot more than we do, especially to surgeons and other specialists with knowledge of anatomy and motion. What other professions are out there deserving attention and able to help us? No surprise: engineers! Among the few people who articulated the forearm of Plateosaurus with ease were two engineers, although I must admit that both had ample experience with biomechanics of humans and other mammals. But that’s a topic for a post of its own, so I’ll stop talking about people and expertise, and turn back to my dinosaur.

“How do these go together? Where’s the manual? HELP!”

If you are a parent and have ever tried to assemble a toy for your kids you probably know the above line only too well. And that’s how I felt about GPIT 1, once I had bones extracted from the CT slices. OK, the skull goes in front, the vertebrae were numbered, that much was clear, the girdle elements and limb bones are handed and thus easy to place roughly, only the fine details will be a bother – or so I thought. Problems surfaces immediately: the dorsal vertebrae had been misplaced on the armature of GPIT 1, so that I had them in the wrong order initially, too. The pelvic girdle elements of GPIT 1 are deformed, and do not fit half as well as they should. And the biggest problem was that I received the animal’s digital skeleton piecemeal, because of the time and effort required to de-mount, prepare for transport, transport and scan the bones (another thing worth a short discussion, by the way). Then, the 3D shapes had to be extracted and cleaned, the latter step being quite cumbersome and time consuming because of the 1-million-parts-3D-puzzle nature of many bones, and because of my inexistent to minimal expertise with the programs we had available for the task.

The first time I tried to articulate two vertebrae I could make neither head nor tail of them. Having a real, 3D object in your hands is a totally different thing than looking at a 2D image of it on a screen, even if you can rotate the view freely. I quickly overcame the problems of translating one or several 2D views into a proper 3D understanding, using unfamiliar CAD software to move several objects around and into proper relation with each other, and handling lots of files way too big to be handled comfortably by the PCs I used. (Shut up, Mike! I can hear you laughing, but you have no idea what the standard level of equipment is at a German university!) In the end I managed, and the PE paper contains the proud results.

Enough prosauropods; I hope we will soon have a post by an author of another paper from the last issue.

References:

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.

Faux, C.M. and Padian, K. 2007. The opisthotonic posture of vertebrate skeletons: postmortem contraction or death throes? Paleobiology 33:201-226. doi:10.1666/06015.1.

Galton, P.M. 1971. Manus movements of the coelurosaurian dinosaur Syntarsus rhodesiensis and the opposability of the theropod hallux [sic]. Arnoldia (Rhodesia) 5:1-8.

Huene, F.V. 1926. Vollständige Osteologie eines Plateosauriden aus dem schwäbischen Keuper. Geologische und Palaeontologische Abhandlungen, Neue Folge 15:139-179.

Paul, G.S. 1987. The science and art of restoring the life appearance of dinosaurs and their relatives. A rigiorous how-to guide, p. 5-49. In Czerkas, S.J. and Olson, E.C. (eds.), Dinosaurs Past and Present Volume II. Natural History Museum of Los Angeles County Press, Los Angeles.

Stevens, K.A. and Parrish, J.M. 1999. Neck posture and feeding habits of two Jurassic sauropod dinosaurs. Science 284:798-800.

Stevens, K.A. and Parrish, J.M. 2005a. Digital reconstructions of sauropod dinosaurs and implications for feeding, p. 178-200. In Curry-Rogers, K.A. and Wilson, J.A. (eds.), The sauropods: Evolution and Paleobiology. University of California Press, Berkeley.

Stevens, K.A. and Parrish, J.M. 2005b. Neck posture, dentition, and feeding strategies in Jurassic sauropod dinosaurs, p. 212-232. In Carpenter, K. and Tidwell, V. (eds.), Thunder Lizards: The Sauropodomorph Dinosaurs. Indiana University Press, Bloomington.

Taylor, M.P., Wedel, M.J. and Naish, D. 2009. Head and neck posture in sauropod dinosaurs inferred from extant animals. Acta Palaeontologica Polonica 54:213-220. doi:10.4202/app.2009.0007.

Senter, P. and Bonnan,  M. 2005. Evidence for obligate bipedality in the basal sauropodomorphs Plateosaurus and Massospondylus. SVP Meeting Abstracts 2005, Journal of Vertebrate Paleontology 25(Supplement to 3):114A.

(yes, the zotero style works just fine!)

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7 Responses to No 4WD for Plateo!

  1. I think this is one of the most important blog posts I’ve seen on palaeontology, and I hope it gets the readership it deserves. I’ll certainly be linking to it from SV-POW! the next time I post there.

    The more I look at the neck skeletons of sauropods and the necks (skeleton and whole) of extant critters, the more I find myself thinking the exact same things you highlighted as the headings in this post: Ask your doctor for advice. Palaeontology is an interdisciplinary science — we just tend to forget. Have you ever read the Journal of International Orthopaedics? How do these go together? Where’s the manual? HELP!.

    In fact, I think that (the whole thing) should be the new official slogan of palaeobiologists.

    • Heinrich says:

      Mike, I wrote this a while ago when on holiday, forgot to post it (blush), read your camel neck post and immediately remembered to post…. guess why? ;)

      You’re exactly right: we are flying blind, as I already noticed when working on Plateosaurus. Sadly, much of what I wrote about motion range must be regarded as at best a best estimate based on bones, but certainly far from reality :(

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  6. Mark Robinson says:

    Just popped in from SV-POW! Excellent post and I echo Mike’s sentiments.

    Seems like that there have been quite a few posts recently (on the palaeoblogs I visit) about the benefits of interdisciplinary involvement or simply observing and studying what happens with extant animals and ecosystems. This can only bode well for science as a whole, and hopefully we’ll have no more hearts in necks or sauropod lawnmowers (I know there was no “lawn” as such back then!).