Photogrammetry tutorial 5: a little visual aid for you

Here’s a little video I cooked up to show the turntable photography method I described in part 3 of this series. I do not wish to part with the dough to buy the video update for WordPress, so please find the file in a download here. It needs renaming to tutorial.zip, then you can un-zip the file and watch the video. AGAIN: you must rename the file so that the ending is ZIP, not PPT!

Teaser images:

034 markers scale_bar

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Holding hands with Plateosaurus

Although I did not start my professional career in palaeontology as a dinosaur researcher, but (can you believe it?) as a palaeobotanist, the Upper Triassic basal sauropodomorph dinosaur Plateosaurus engelhardti from Central Europe has been accompanying me for a very long time. When I started my studies of geology/palaeontology at the University of Tübingen, two mounted skeletons stood in a second floor hall of the institute, which triples as a lecture hall, office and museum building. These mounts, erected under the direction of Friedrich von Huene, still stand there today, although (thanks to a new curator) the room looks much nicer: the window had been bricked over, but has by now been restored.

Sauriersaal_Tue_rechts_sm

One of the two skeletons, GPIT/RE/7288 on the right, later became the guinea pig for my doctoral thesis. However, although it is beautifully preserved and nearly complete individual, some parts of the skeleton were replaced for my digital range of motion studied with parts of the other skeleton, informally known as ‘GPIT Skelett 2‘ (on the left). This included the hand, because the left hand of ‘Skelett 2’ is in very good condition compared to the left hand of GPIT/RE/7288. Because the two skeletons are of nearly equal size (in fact, the three skeletons are; ‘Skelett 2’ is a composite made from two individuals), the mixing of the bones was not a problem. However, although many elements of the hands of GPIT/RE/7288 are preserved, I decided to use the complete left hand and lower arm of ‘Skelett 2’ in one piece, so that any problems that might arise from the bones stemming from different individuals would be limited to one joint, and not mess up the wrist of metacarpus.

The bones were all CT-scanned at the University Hospital of Tübingen University, by the very helpful Dr. Ludescher, and I extracted the 3D shapes in long nights at the museum, mainly spent waiting for the computer and hoping it wouldn’t crash again. Comparing those extractions to similar work today just serves to show me how old I am: computers have become so incredibly much faster and have so much more memory that, although I have witnessed the process, I can scarcely believe it.

The resulting files were the basis of my two ‘Digital Plateosaurus’ publications in PE and APP, as well as my thesis. During that work, I limited myself to analyses of the skeletal range of motion that dealt with the big questions of posture (bipedal or quadrupedal) and major limb and body motions. I took quick peeks at foot posture and hand function, but didn’t do detailed analyses, as I did not feel competent to do so. That the manus was mainly a grasping or digging organ, and did not play a significant role in locomotion, was obvious to me from the simple fact that both I and, a short time earlier, Bonnan and Senter (2007) had found that Plateosaurus was incapable of sufficient pronation (turning the palm down) to walk on its hands, and thus had to have been a biped. My modelling of the centre of mass (a line of research that I am still pursuing, see my latest paper in Fossil Record) showed that Plateosaurus was well balanced as a biped, and a bit of whimsical whole-skeleton posing showed that a quadrupedal posture looked rather ridiculous.

Plateo_pose

From here: Virtual skeleton of GPIT/RE/7288 in quadrupedal poses in lateral view. 1: Digitigrade, 2: semi-plantigrade, 3: plantigrade hindlimb. 4: as 3, but with vertically positioned femur at midstance. 5: equal limb length posture. Length of left femur is 595 mm.

However, a tiny bit of nagging doubt always remained: I knew that there was a lot of cartilage in dinosaur skeletons, much more than in mammals, and what if I had been wrong about the pronation issue because of that?

Skip ahead a few years. I had been busy with other work, but the Plateosaurus hands and feet were still on my mind. And then an opportunity presented itself to come back to one of these issues and do a detailed study of the hand’s ability to support the animal’s weight, or grasp things. A student in Bonn at the Steinmann-Institute, Stefan Reiss, was looking for a diploma thesis topic, and willing to undertake the gruesome task of modelling the Plateosaurus manus.

Stefan dug right in, although we faced a number of challenges. First of all, the spatial separation between Berlin and Bonn, second, the fact that he had to try and serve two masters (me for the computer aided engineering modelling work and Martin Sander in Bonn as the official supervisor of his thesis work and for the palaeontological aspects), third a long and arduous variety to computer problems – it all conspired to make the work more difficult. However, in the end Stefan got things done, and received his diploma. I’ll spare you the ugly details how we managed to coax the data out of the PC, using a software for which support was yanked out from under our feet (don’t you hate commercial programs?) during the study.

Next step, obviously, was publishing the results. Again, things proved difficult. I can today laud Stefan for improving his English a lot while writing his thesis and the paper, but at times I wanted to find all his former English teachers to give them a stern talking-to. Also, because the program had run out of license, as it was not sold any more, we couldn’t happily go and create figures any way we wanted, but had to live with what had accumulated for the thesis. Stefan quickly learned how to handle the Computer Aided Design and the Computer Aided Engineering program, and started out on a series of experiments that I will only partly describe here – namely, as far as they are included in the current paper.

We had decided early on that the paper would go to PE – after all, PE is open access and asks no fees, neither from readers nor authors. That’s because of the funds provided by PE’s sponsors and because of the many volunteers who work for the journal, which includes me in the function of style editor. Unlimited colour figures, unlimited length, a lack of false pretence about the “importance” of the journal and whether the paper is “important” enough – what more can you ask? Thus, off to PE the paper went (and no, I have no influence whatsoever on the editorial process).

In the end, as is often the case, the review process proved very helpful, even though it was a tiny bit frustrating. I sometimes complain that reviewers should not ask that authors “write a different paper”, and for good reason: a reviewer’s job it to check on what you did do, and how you present it, not what you might have done differently for the last six months or two years, if you had back when you started known where your research would take you, and what the personal whims of the reviewer are. In this case, however, the reviewer didn’t suggest that we toss our existing paper, but rather that we re-think the entire publication strategy. He suggested that we cut the paper in half, with the first half being what you can now read in PE. The second half, he said, should be expanded with lots of additional work, and then published as a second paper. And this approach makes a lot of sense: Stefan gets a paper published now, a paper that isn’t too long and over-complex, and we also get to publish the rest of his work, albeit later and after some serious time and money investment. However, that second paper will then really rock!

So we decided not to fight, but to accept this review, and adapted our manuscript as suggested. It now is narrowly focussed on the question: Does the hand of Plateosaurus show a range of motion and robustness compatible with regular use during locomotion? And the answer is a resounding NO! The third finger is long and flexible enough to have been used in locomotion, but it alone is far too weak to carry a significant part of the animal’s weight. The second finger could share the load, but both together are still a far cry from sufficient support. The other fingers are too short, and/or weak, and/or too immobile. What’s more, the pattern of mobility doesn’t fit together, so that the forces would not be properly distributed between the fingers. But, quite the reverse: the fingers turned out to be very good as flexing, thus grasping things!

(What must be kept in mind is that “locomotion” doesn’t mean taking tiny shuffling steps while feeding, but actually going places – sustained change of location. Nobody is saying that the hand couldn’t be used as a prop while the animal was drinking or feeding from the ground.)

cross sections

Digitigrade or not? Preuschoft’s method in action on the hind limb of Plateosaurus. The cross sections of the bones above and below the ankle joint that were involved in carrying the animal’s weight (tibia+fibula; metatarsals II-IV) are nearly equal, indicating a digitigrade posture.

Additionally, we used a smart method Prof. Preuschoft once taught me to calculate the relative strength of the metatarsus and lower arm in comparison. If an animal walks in a digitigrade posture, i.e. with only the toes touching the ground, it is reasonable to assume that the sections of the limb are roughly equally robust, because they are under roughly similar loading regimes. Obviously, it plays a role how much weight really is on them: the thigh doesn’t carry the load of rest of the limb it is part of. Also, what angular excursions occur? The bigger the angles the higher the bending loads. But neighbouring elements in the distal limb should see roughly similar regimes. Thus, the cross sections of tibia+fibula (close to the distal end, but not at the articular ends, where shapes are also defined by the necessities of the joint) and the metatarsals should be roughly equal. If, on the other hand, the animal is plantigrade, a big part of the weight is carried on the heel, and the metatarsals can be slimmer. Preuschoft tested his theory on the hands of monkey, some of which walked in digitigrade posture, some in plantigrade, and the results matched the predictions. (sorry, I have lost the reference – oops!) So we did the same thing for Plateosaurus, forelimb and hind limb (data on the latter not in the paper, so see figure above) and guess what: the hind limb indicates a digitigrade posture, but the much shorter forelimbs indicates plantigrady! So, the limb that is too short anyway is further shortened in its functional length by being forced into a platigrade position? That makes no sense whatsoever.

In all, what Stefan showed in our paper is more nails in the already sealed shut coffin of plateosaur quadrupedality. The other part of your combined work, the part that we’re holding back for the next paper, will be more positive, telling us about what the animal could do, not what it couldn’t. That’s always more fun, but also usually more speculative. It will take us a while, though.

My thanks go to Stefan, logically, as well as to Martin Sander and the entire PE team. It is a pleasure to publish in a completely free (no author fee, no reader fee), i.e. true open access journal. I am also very grateful for the two reviews by Matteo Belvedere and Matthew Bonnan! Although one of them gave me quite a head-ache and made us totally re-vamp the paper, both reviews were fair, to the point, and very helpful.

 

Posted in "Prosauropoda", 3D modeling, anatomy, Biomechanics, classic CAD, Digitizing, Dinopics, Dinosauria, locomotion, Navel gazing, Open Access, papers, Plateosaurus, Sauropodomorpha, Tübingen | Leave a comment

Osteoderm distribution does not significantly influence the center of mass of stegosaurs

Today, a new paper came out in Fossil Record, a journal that as of Jan 1, 2014 is open access (so go read the paper! It’s free). The paper tests hypotheses about the position of the centre of mass (COM) of stegosaurs and how variations in the distributions of osteoderms (plates and spikes) influences it, and whether rearing behaviour gave stegosaurs especially sturdy forelimbs.

It is a pretty boring paper, overall, and the method used – well, let’s say it conforms to the German proverb of shooting at sparrows with cannons (i.e., using a far too big gun for the purpose; similar to the English phrase to crack a nut with a sledgehammer). Let me explains what the paper deals with, and why a much simpler approach would have been sufficient – and why it was not adopted.

The paper checks whether two hypotheses previously published by Maidment et al. (2012). In a very interesting and thorough study they found that “the largest stegosaurs have relatively slender humeri in comparison with the smallest members of the clade”, and proceed as follows (Hypothesis 1): “This could be due to changes in the center of mass related to distribution of dermal armor; for example, Kentrosaurus, the smallest stegosaur in the sample, is known to have possessed parascapular spines [Galton (1982)]. Despite the large number of individuals of Stegosaurus known, no parascapular spine belonging to the genus has ever been discovered [Galton and Upchurch (2004)]. The additional mass of these large dermal spines in the shoulder region might have caused the center of mass to be located further anteriorly in Kentrosaurus than in Stegosaurus”.

In short, Hypothesis 1 says that the forelimbs of Stegosaurus were proportionally less strong than those of Kentrosaurus because they did not have to carry as much weight, because Stegosaurus did not have spikes on the shoulders. In fact, the hypothesis is supposed to be a general rule, and Maidment et al. (2012) picked a specific example: S. and K. and shoulder spikes.

Hypothesis 2 deals with the fact that all stegosaurs have proportionally very robust humeri compared to other ornithischian dinosaurs. Maidment et al. (2012) suggest that “[...] the robustness of stegosaur humeri could be related to a specific behaviour. For example, it has been suggested that stegosaurs utilized a tripodal stance [...]; perhaps increased stress on the humerus was generated during rearing as a result of pushing off from the ground.

Both ideas make sense at first glance: more weight means higher forces, and thus more sturdy bones. And higher forces from larger exertion while attaining an unusual pose would also mean more robust bones. So how to test this?

If Hypothesis 1 is correct, we can predict that the additional amount of weight born by the forelimbs is large in relation to the weight that would be born if there was no shoulder spike in Kentrosaurus (i.e., we can check K. with and without shoulder spike), and we can do the same for Stegosaurus. If the spike only adds a few percent to the load, the hypothesis is not supported. So let’s do that:

Figure_01

Figure 1 from the paper shows (top) a 3D model of Kentrosaurus, with the osteoderms distributed the way Janensch and Hennig reconstructed them (Hennig 1925; Janensch 1925) (scale bar 1 m). Also, there are four versions with alternate distributions. Each distribution has its own colour, and the big model has the centre of mass position shown in the corresponding colour for each version. Between red and green the sole difference is that the spike that Janensch put on the hip is moved to the shoulder. Thus, we can see how much of a difference the presence or absence of a should spike really makes – in fact, in this case the effect is exaggerated, because the spike is not “there” or “not there”, but “there” or “elsewhere”, i.e. it moves the COM backwards in the test case where it is not on the shoulder instead of having no influence. And as the enlarged inset shows (scale bar 10 cm) the influence is minimal! Moving the spike moves the COM by a paltry 10 mm, says Table 1 of the paper! That adds a whopping 1% of body weight to the load the forelimbs have to carry, up from 16% to 17%. That is a 6.25% increase.

In the lower half of the figure you can see a Stegosaurus 3D model, in this case with the hypothetical shoulder spike in blue. Adding it moves the COM from the red dot to the blue dot – again only 1% of body weight and a COM motion of this time only 6 mm.

Ergo, Hypothesis 1 is not supported. However, Maidment et al. (2012) gave the shoulder spike as an example only. So what if we move a larger number of osteoderms around? Will that have a big influence on the COM position?

Yes, we can make the COM move quite a bit. However, that requires putting all osteoderms that we know Kentrosaurus had to the neck (light blue), whereas the influence of moving the trunk osteoderms only to the neck, or of moving all tail osteoderms to the tail tip, doesn’t really have a big influence. We can thus conclude that we need to do absurd things to put a lot more (or less) weight on the limbs. Moving a single pair of spikes is not the cause of the more robust forelimbs in Kentrosaurus compared to Stegosaurus.

So what about hypothesis 2? What do the models tell us about it? Both models show a highly similar overall body shape, and accordingly highly similar COM positions. We can now measure the moment arm of the COM versus the hind feet, as well as that of the forefeet. The ratio between the two is nearly 5:1, i.e. a five-fold advantage for a push-up motion. And much of the torque needed to rotate the body up into a tripodal pose as in the picture below would be produced by the hindlimb and tail muscles anyway. The COM position is, in fact, similar to many other big ornithischians, some of which supposedly also fed in a more upright stance. Thus, the claim that rearing forces such sturdy forelimbs onto stegosaurs is also not supported. In sum, this is a seven page paper that simply says “nope, that’s not correct”, but can’t really offer anything new.

rearing

Rearing Kentrosaurus digital skeletal mount, from Mallison (2010).

So, why did I say all this work was cracking a nut with a sledgehammer? Because the easy way would have been to simply calculate the volume and from it the mass of the shoulder spike. All the osteoderms together make up only ~ 3.5 % of the total body weight of Kentrosaurus! The spike alone, and even a large number of spikes and plates combined, can’t have much effect. With regards to hypothesis 2 it is sufficient to check the published literature, e.g. Henderson (1999), to see what the COM position of stegosaurs is, and that it is not unusual compared to other, slender-forelimbed ornithischians. Therefore, all the fancy 3D modelling is not needed.

Why on earth then did I bother you with it in this post? And why is it in the freakin’ paper? Three reasons, really:

  • The 3D models visualize the osteoderm placement variations and their effect on COM position very nicely, making it very easy to grasp what’s going on.
  • The method that’s used to calculate the COM positions is very easy and fast, and it is always worth publishing the little tricks. In this case the time saves versus other methods was lost building the models, but you can do more complicated stuff with the method, and save quite a lot of time – if you know it.
  • I wrote the paper, and I like my 3D models.

Yeah, the last bit I guess does not come as a big surprise now ;)

I’ll have more to say on this paper, especially on its review history (lessons to be learned by all, and in this case [as normally] I must really laud the reviewers and editors!), but that will have to wait a few days.

References

Galton, P.M. 1982. The postcranial anatomy of stegosaurian dinosaur Kentrosaurus from the Upper Jurassic of Tanzania, East Africa. Geologica et Palaeontologica, 15:139–165.
Galton, P.M. and Upchurch, P. 2004. Stegosauria, p. 343–362. In Weishampel, D.B., Dodson, P., and Osmolska, H. (eds.), The Dinosauria, 2nd Edition. University of California Press, Berkeley.
Hennig, E. 1925. Kentrurosaurus aethiopicus Die Stegosaurier-Funde vom Tendaguru, Deutsch-Ostafrika. Palaeontographica, : 2 Supplement 7:101–254.
Janensch, W. 1925. Ein aufgestelltes Skelett des Stegosauriers Kentrurosaurus aethiopicus HENNIG 1915 aus den Tendaguru-Schichten Deutsch-Ostafrikas. Palaeontographica VII 2 Supplement 7:255–276.
Maidment, S.C.R., Linton, D.H., Upchurch, P., and Barrett, P.M. 2012. Limb-bone scaling indicates diverse stance and gait in quadrupedal ornithischian dinosaurs. PLOS ONE, 7(5):e36904. doi:10.1371/journal.pone.0036904.
Mallison, H. 2010. CAD assessment of the posture and range of motion of Kentrosaurus aethiopicus Hennig 1915. Swiss Journal of Geosciences, 103:211–233. doi:10.1007/s00015-010-0024-2.

Posted in 3D modeling, Biomechanics, classic CAD, Dinosaur models, Dinosauria, Kentrosaurus, Ornithischa, papers, Stegosauria, Stegosaurus | 4 Comments

A wonderful Plateosaurus watercolor

Last fall, on my big US round trip that ended with the SVP meeting, I spent a few days in New York, working on photogrammetrizing oviraptors (two links) at the AMNH. One evening I spent with the incomparable Gary Vecchiarelli and equally incomparable Christopher DiPiazza, drinking beer, talking dinosaurs, shooting the shit – a fun evening I hope to repeat as soon as possible. Chris and Gary are Jersey boy, and they love dinosaurs – what surprise that there is a matching blog: Jersey Boys hunt Dinosaurs.

Chris surprised me with a present. I’d previously given him some advice on a Plateosaurus drawing, and well – see for yourself:

ChrisD_Plateo

 

Very many thanks again, Chris, for a wonderful watercolor of my favorite dinosaur :) (I’ll email you the full-res scan). Love the pose, and the proportions are perfect!

Posted in "Prosauropoda", Dinopics, Dinosauria, FUN!!!, Palaeoart, Plateosaurus, Sauropodomorpha | 2 Comments

busy times…..

This place has grown terribly quiet recently, and I apologize to those who’re keenly awaiting the next post on dinosaur mounts……

Just kidding! I know all you wait for is the latest rant :) However, although there is plenty to rant about (and preciously little to rave about, although a few very kind people have been very good to me recently) – anyway, although there is much I could rant about right now, but I don’t have time.

There are a ton of things I really need to do very urgently, and whenever I attack one, another more important one crops up. Right now I need to finish, by last Tuesday:

  • submit a grant request
  • write another grant request
  • ready 3 papers for submission (two cases: re-first-submission), each requiring about a month of work.
  • resubmit two papers (edit: 12 hours laters both are now on their way! Yay!), minor changes required
  • finish two very important and urgent SIMM models
  • finish a bunch of 3D models of bones
  • pack for China
  • go shopping so the family stays afloat while I’m in China
  • do a LOT of style editor work, much of which is way overdue
  • find a job, ASAP!

So all I have for you today are a bunch of photos, as teasers for upcoming posts (in a year or two or so).

squirrel_01

Woodpecker_01

Yes, a “behaviour” post, with illustrations from my garden, that’s to come soon!

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Photogrammetry tutorial 4: bulky stuff

Previously, I had much to say about photographing specimens that you can move around and nicely place on a turntable. However, the world of vertebrate palaeo holds many specimens that do not fit into that category. Specimens that just generally do not fit at all, anywhere. Specimens like sauropod sacra, huge chunks of fossilized and therefore rock-heavy bone that you need a forklift to move. Beaten only by sacra with still-attached ilia. Oh, and obviously beaten by stuff too heavy to move at all placed in storage so that it is barely accessible. Like hips with a shelf right above them. Like this one:

Vernal_hip01

As you can see, the next shelf isn’t far above. Luckily, there is some room, and there are aisles on both sides. This is in the Utah Field House of Natural History State Park Museum. The layout in the photo below (AMNH Big Bone room) is much worse, because the specimen is facing the wall:

AMNH_bigbone

How did I deal with the rather suboptimal conditions in Vernal?

First of all, I took photos with long exposures. The light wasn’t too bad, as there were long banks of fluorescent lights down both aisles, and behind me (on the photo above) there was a row of those gloss white painted collection cabinets that do such a neat job of reflecting light. So there was light coming in from many directions, and the shadow thrown by the shelf above wasn’t as hard as it could have been. But the level was, overall, rather low. Long exposures meant that I needed to use a tripod, which had the added benefit of “allowing” me to fiddle with the tripod until I got the perfect composition for each photo. It takes forever, compared to speedy hand-held shots, but in the end that time is easily compensated for by the lower number of photos needed, because each photo is better composed.

A specimen in confined quarters – and being very close to the ground is a confinement in that sense, too – requires a lot of variability in the tripod. Check out what I did to get good shots from a low angle, in order to capture as much of the lower edges and ventrally directed surfaces of the sacrum:

Vernal_hip02

Yup, that looks pretty contorted! But it allowed me to take photos like this:

Vernal_hip03

Look how nicely the surfaces on the underside show up!

So, how do you photograph such huge immobile specimens?

Ensure good lighting

In the case shown above, there was no need to bring additional lights. However, be prepared to set up a few lamps and use white cardboard as reflectors to light up the lower surfaces of the specimen.

Use long exposure times and a tripod

well, duh!

Take hand-held HDR shots

a contradiction to the last statement? No! To properly document the top of the specimen you may need to combine both methods. Or, in fact, take sets of photos of the complete specimen with both methods. Also, do not be afraid of taking the camera off the tripod and pressing it against the bottom surface of the next higher shelf to hold it steady; this gives you excellent top-down shots. or even use the flash!

Vernal_hip04

This is a HDR shot, for which I held the camera under the next-higher shelf and aimed blindly.

Select views to maximize the coverage of the specimen’s surface

This may mean hanging a sandbag from your tripod as a counterweight and sticking the camera between the shelves! Most tripods have a small hook for this purpose.

If you follow these rules you will likely get pretty good results!

Vernal_hip06

Vernal_hip05

Vernal_hip07

Posted in 3D modeling, photogrammetry, photography | 5 Comments

Dinosaur mounts at the NHM L.A.: Camptosaurus

As I am writing this, more and more remarks on the general layout of the hall creep in. I promised to discuss the Camptosaurus next, and I am too lazy to remove those remarks and turn them into a post of their own, so you’ll have to live with the added yadda-yadda ;)

One of the most-ignored dinosaurs of the American West, specifically the Morrison Formation, is certainly Camptosaurus. Aside from the immediate association “camp-o-saur” that gives it a somewhat homey, boring sound, it has no big teeth, no big claws, no exceptional size going for it. Not even baby camptosaurs in spectacular nests or so, just a really scrappy partial embryo (laudably described in loving detail by Chure et al. 1994). BLEH! If you do not believe me, check out the wikipedia page! For such a well known dinosaurs it is surprisingly sparse. The scarcity of information may, however, also have to do with a lack of spectacular research – after all, C. is boring, so why study it any further?

Camptosaurus is a roughly Plateosaurus-sized animal (seems it can be a tad bigger), and has surprisingly similar proportions: a small skull, a long neck, short forelimbs, a body that is easy to approximate with an ellipsoid that has a long axis roughly 1.5 times as long as the two other axes, rather sturdy-looking hind limbs, and quite a long and deep tail. The similarities do not end there, but I won’t waste the material for a good paper right now. Suffice to say that the basic dinosaurian herbivore bauplan, as exemplified in “prosauropods”, seems to have been quite a successful construction – after all, here’s an ornithischian taking it up again to the same size in the Late Jurassic!

LA_Campto001

Here’s the NHM L.A. Camptosaurus mount in all its splendour. From this perspective the animal seems to be all hindlimbs and tail…..

LA_Campto002

…whereas a look down from the mezzanine level shows quite some bulk in the anterior body. Also, the enormously flaring preacetabular processes of the ilia show up nicely, indicating quite some soft tissue mass around the hip that the other bones alone (e.g., the posterior dorsal ribs) would not immediately suggest. As in Plateosaurus! But enough of similarities, what are the differences?

Aside from the obvious differences in the shape of the hip bones – no flaring preacetabular processes in Plateosaurus, not even any long preacetabular processes at all, non-retroverted pubis (and a very broad one at that) – there are other differences as well, although I am sure they are not obvious immediately to laypeople. For example, instead of the long and slender cervical ribs of Plateosaurus, Camptosaurus has fairly sturdy ones that stick rather far out to the sides. Add to that the fact that as far as we know there are no osteological correlates for air sacs in ornithischians, whereas they exist in the form of pneumatic foramina in the neck of Plateosaurus,and it seems that the neck and anterior trunk of C. was quite a bit heavier for the same size than that of P. Also, the front limbs are quite a bit longer proportionally. If we add that up it quickly becomes apparent why I do not have any issues with the quadrupedal posture of the NHM L.A. mount: Camptosaurus possibly was capable of quadrupedal locomotion! It’ll take me some detailed study to form a firm opinion, but on the basis of what I see and know I can’t exclude the option of a quadrupedal pose right now.

Obviously, I’d like to take a very close look at the elbows and hands, so let’s have a zoomed view of a suitable photo:

LA_Campto003

There you go, an anterior view of the lower forelimbs of the mount, from a slightly lateral point of view. For those not that deep into forelimb anatomy and mobility, here’s a few pointers: the two long bones of the lower arm, radius and ulna, are here correctly articulated to the humerus, with the slender radius on the lateral condyle, and the sturdier ulna on the medial condyle. Yes, sounds like a dumb thing to mix up, but it’s been done, as I found when I took a close look at Plateosaurus. In museums. Big ones. Also correctly, the radius leads to the thumb, not the little finger. Which explains why the shaft of the radius crosses over the ulna to place the palm flat on the ground. And this is where I do take issue with the mount, although it is not a major point!

Take a close look at the left hand, the one that is on the ground. It is placed so that the entire hand is flat on the ground, i.e. plantigrade. The feet, barely visible in the close-up but well visible in the first photo above, are in contrast digitigrade. I have a hard time believing that an animal with such an unfortunate ratio of limb lengths as Camptosaurus (or even worse, Plateosaurus) would give away the additional forelimb length that a digitgrade or even unguligrade (only the distal-most phalanges touch the ground) posture would give! Especially when we’re talking animals that come from bipedal ancestors, where the by far easiest and simplest way of gaining a support point in front is to put the finger tips down with the palm pointing medially, which is the ancestral direction.

OK, enough of my biomech whining now, and more describing the mount’s effect in the context of the exhibit. Let’s have a look at the whole hall again:

LA_08

Can you see the Camptosaurus? It is right there, behind the skull of the Tyrannosaurus on the right.

As you can see, the focus of the hall is on something entirely different. Smack in the middle there is a group of an adult, a subadult and a baby Tyrannosaurus, and that’s quite clearly the center of attention. On the inner long side of the hall there are ceratopisan skulls and so on, and the window side was some small stuff on the pedestals that hold the big mounts. The two short sides hold a combined assemblage each, in the photo above the stegosaur-allosaur combo and various others are behind, and the Camptosaurus is paired with a (disinterested in it) Carnotaurus and various other fossils, too.

For visitors, this works very nicely. You can enter either in the middle of the wall behind the position I stood in when I took the shot above, or at the corner to the far right from it. That entrance leads directly up to the Camptosaurus, with the Carnotaurus behind it, and a large glass cabinet to the right. The base below the mounts invites you to circle the two dinosaurs either counter-clockwise (i.c., check out the stuff in the glass cabinet first), or clockwise, which means focussing on the mounts. or you can just walk by and drift over to the rexes, if you’re less into dinosaurs.  I noticed that most people took the last option, but were later circling the rexes in a way that brought them back to the Campto/Carno bit, which they then circled. All in all, the layout keeps people in the room and looking at the exhibits, which means that they spend more time engaging with the exhibit than a classic layout with specimens on the left and right and a big aisle or a one-big-chunk-in-the-middle exhibit would. Berlin, for good reasons, has such a big chunk, and I do see a lot of people passing by half of the hall (the MfN tricks them into coming back later, though).

If you come into the hall at the stegosaur end, you end up walking around the rexes, and on either side your gaze will automatically fall onto the Campto/Carno mounts. Repeatedly, I watched people who’d obviously had enough of dinosaurs already (judging by their obvious impatience and the slight acceleration of their walk) slow down again and take a closer look, simply because the mounts are along their path, but not blocking it.

LA_Campto004

Here’s a view from the entrance. Camptosaurus looks like the doofus it is.  No, you’re not drunk. I tilted the camera a bit to get the Carnotaurus to fill the entire width of the pic to maximize resolution.

The glass cabinet on the right holds various dinosaur feet, in the back you can see another with a skull of Edmontosaurus and Tyrannosaurus each, to highlight the tooth batteries of duckbills and contrast them with the basal dinosaur teeth and their replacement. Next to them there’s an Argentiosaurus vertebra (cast). I like how the museum combines the various educational bits and the big mounts.

But, OK, back to the mount. One thing I am not happy with on it that I have not mentioned so far. It is pretty obvious in the frontal shot above. Let me show you a closer view from a slightly different angle, one that makes the problem even more obvious:

LA_Campto005

What in the name of all extant and extinct archosaurs is that gap between the coracoids? Did the poor critter swallow a hand grenade and is in the act of blowing up? That gap is wide enough to float a whale through (OK, exaggeration). But seriously: there should not be such a huge gap! There is some debate about how steeply the scapula should be angled, and how high it should be placed on the ribcage, and how much cartilage there was between the coracoids (mostly between&below), and how exactly the sternals were shaped and placed, and whatnot. And yes, sternals weren’t know in C. for a long time, but Dodson and Madsen (1981) described them very nicely. Now, check out a mount of Camptosaurus in the ROM, photo on wikimedia. Much better! (Yes, some people think they were obligate bipeds, thus the warning label on the photo’s page. And as mentioned: more research needed.)

OK, enough on the “boring” ornithischian! Next time we take a closer look at a carnivore, Carnotaurus.

References

Chure, D., Turner, Ch. and Peterson, F. 1994. An embryo of Camptosaurus from the Morrison Formation (Jurassic, Middle Tithonian) in Dinosaur National Monument, p. 298-311. In Carpenter, K., Hirsch, K. F. and Horner, J. R. (eds.), Dinosaur Eggs and Babies. Cambridge University Press.

Dodson, P. and Madsen, J. A. Jr. 1981. On the sternum of Camptosaurus. Journal ofPaleontology, 55(1): 109-112.

Posted in Dinopics, Dinosauria, Iguanodontia, NHM L.A., Ornithischa, Ornithopoda, Travels | 5 Comments