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Tetrapod Zoology

Tetrapod Zoology

Amphibians, reptiles, birds and mammals - living and extinct

The Second International Workshop on the Biology of Sauropod Dinosaurs (part II)

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An average day in the Mesozoic. This >definitely< happened! Illustration by Luis Rey.

ResearchBlogging.org

And the ornithodiran biology fest hasn’t stopped yet… I still need to finish up on the events of the sauropod biology workshop, the three-day meeting held in December 2011 at the University of Bonn, Germany. For part I of my thoughts, please go here.

Having finished with feeding and digestion, an entire session was then devoted to sauropod reproduction and life history. This is one of those areas that we long to know more about – there isn’t much direct data, so what we can infer based on the extensive information we have on other animals? Jan Werner used data from extant animals to argue that body mass is correlated with reproductive investment, but predicted sauropod clutch sizes differ if we assume avian rates or ‘reptilian’ rates. Counter-intuitively, perhaps, an avian model predicts a much higher annual egg number.

One of the most characteristic bits of a sauropod. Diagram compiled by Mike Taylor.

Physiology and growth rates formed the subject of a few talks. Thomas Tütken explained clumped isotope thermometry (CIT) and what it might mean for sauropod body temperatures. This work is reasonably well known thanks to Eagle et al.’s (2011) paper in Science. The isotopic data seem to show that sauropods had a body temperature similar to that of endothermic mammals, and 4-7 degrees C lower than would be expected if they were mass homeotherms. Romain Amiot’s talk focused on Cretaceous thermal regimes and how they might correlate with sauropod distribution. He spoke in particular about the recent work showing that Early Cretaceous Liaoning was apparently cool-temperate (mean air temperature something like 10 deg C) (Amiot et al. 2011). And, yes, there was some discussion afterwards about the absence vs presence of crocodilians at Liaoning. Note that, even if they are there, they’re evidently very rare.

Data from osteocyte lacunae, discussed by Koen Stein, seem to provide further support for the concept of elevated metabolisms in Mesozoic dinosaurs. Steven Perry spoke about sauropod lung structure (as inferred from crocodilians and birds). Thanks to recent work on crocodilian lungs, we now know that unidirectional airflow is not unique to birds (Farmer & Sanders 2010), but probably evolved early on in archosaur evolution. The crazy-long tracheae and oesophagi that sauropods must have had raise all kinds of questions about breathing, vocalising, swallowing and exchanging heat, but we just don’t have enough information to answer those questions in meaningful fashion. Yet. Could cooling of inspired air in the upper part of the respiratory tract contribute to temperature control?

Vertebral pneumaticity in the non-sauropod Plateosaurus; photo by Matt Wedel.

Matt Wedel reviewed current thoughts and recent developments on sauropod pneumaticity. The absence of skeletal pneumaticity in sauropodomorphs other than sauropods and Pantydraco turns out to mostly be an artefact of not looking hard enough, since recent work has discovered pneumatic vertebral features in Plateosaurus [adjacent photo from here on SV-POW!], Aardonyx and elsewhere among ‘prosauropods’ (Yates et al. in press). And additional recent work has discovered previously overlooked pneumaticity in the tails of several well known sauropods: the cases concerned are particularly interesting since they involve numerous pneumatic hiatuses (where pneumatic diverticula must have been present, yet ‘skipped’ vertebrae without leaving any bony traces). Within the context of what we know about archosaur pneumaticity, ornithischians remain an enigma – did they really lack skeletal pneumatisation entirely, or have people overlooked it, as they long did with prosauropods? Or is it that ornithischians had diverticula, but failed to pneumatise their bones? Regular readers will know about the claimed pneumaticity of the iguanodontian Delapparentia, but this isn’t at all convincing.

Matt Wedel's opening slide. Photo by Vanessa Graff.

We now have so much data on skeletal pneumatisation in sauropods (and other fossil dinosaurs) that it’s difficult to see where research progress might occur – we aren’t going to disprove the hypothesis of sauropod pneumaticity. So – what next? Inspired by the digital modelling work of Heinrich Mallison, Don Henderson and others, Matt suggests that sauropod palaeobiologists work together to construct a digital sauropod that might be used to examine many of our questions about physiology, airflow, temperature gradients across the extremities and so on.

Neck Wars! (continued)

And so, by inevitable progress, we were on to necks. Some of you will know of the Neck Wars, the very much tongue-in-cheek term we use for the academic disagreement that continues between those who think that sauropods could and did raise their necks up high, and those who think that sauropods were more or less constrained to perpetual sub-horizontal neck poses.

Mike Taylor discussed his work on articular cartilage in necks and what it might mean for sauropods (a subject I covered in my discussion of the Lyme Regis SVPCA meeting). Kent Stevens gave a talk essentially similar to the one he presented at SVPCA in Cambridge in 2010 (see discussion here at Tet Zoo ver 2). Kent claimed that there are a number of ‘myths’ circulating about neck postures and the nature of zygapophyseal articulations and that various of the statements made by Taylor et al. (2009) can be challenged. It would be futile for me or my co-authors to respond to Kent’s many points in front of an audience, so our strategy has been (and still is) to hold back and wait until there’s something published to respond to. I want to make one point here though. When you see the neck of a mounted skeleton in a museum, you are not seeing that neck in ONP (osteological neutral pose), nor are you seeing the normal, alert neck pose of the species in question. Rather, people have deliberately posed the skeletal neck you’re looking at to match the angle and posture of the flesh-and-blood neck of the animal when it was alive. But we know from x-rays and dissections that (with exceptions, like flamingos) the angle of the neck skeleton is not the same as the angle of the neck with all of its soft tissues in place. If you’re interested, there a whole article on this specific issue over at SV-POW!

X-rays of diverse living animals show that extension is the norm at the cervico-dorsal junction, and flexion the norm at the cranio-cervical joint. Furthermore, note that the angle and pose of the neck SKELETON is often more vertical than what you'd expect based on the neck's soft tissue outline.

Nicole Klein presented histological data that essentially confirmed what some of us have suspected for a while: that the (often ultra-long) ‘cervical ribs’ of sauropods are actually ossified tendons. Vanessa Graff followed up with an excellent discussion of the ‘ventral bracing’ hypothesis: the idea – published by Martin et al. (1998) and supported by various members of the German Konstruktion Morphologie school – that the cervical ribs somehow prop up against one another and form continuous, permanently loaded, uncompressible struts that run along the bottom of the neck. This model was inspired by the ventral bracing system supposedly present in crocs. But... it isn’t actually present in crocs at all, and there are loads of reasons why it just can’t work. For the record, we know that sauropods also had a dorsal interspinous ligament, and we reasonably infer that they had bird-like neck muscles as well, so it’s not as if they were devoid of other structures that contributed to neck support.

Finally on necks, Don Henderson used mathematical modelling to examine the dynamics of heat loss on the sauropod neck.

Naish, speaking about the 'necks for sex' hypothesis. Many points if you know what's on the screen.

Armitt Schmitt spoke about his work on sauropod inner ear morphology and what it might mean for palaeobiology. I gave the very last talk – a summary of the paper that I and colleagues published in response to Senter’s idea that the sauropod neck might have evolved as a sexual display structure (Senter 2007, Taylor et al. 2011). It was the very last talk of the meeting, so I kept it light and included as many jokes and hilarious images as possible. For time reasons I had to cut out a brief section on mutual sexual selection – kind of frustrating since I wanted to present this phenomenon to the audience. Indeed, the Taylor et al. (2011) paper evaluating Senter’s ‘necks for sex’ hypothesis and the Hone et al. (2011) paper on mutual sexual selection in dinosaurs and pterosaurs can be regarded as linked projects.

And that was it. Three whole days of discussion and debate on just about all aspects of sauropod biology. I believe that most of the talks were filmed, and at some stage they’ll be viewable online. I’ll include a link when I can. How did the gigantism hypothesis hold up relative to the new data, and new ideas, presented and discussed at the meeting? In general it stood up well, and most new research fits into the idea that (as discussed in the part I article) the long sauropod neck, avian-style respiration system and absence of mastication combined with a high metabolic rate and rapid production of babies to allow the evolution of superlative size.

I’ve never been to Bonn before. I got to see some nice fossils, including the holotype of the pterosaur Scaphognathus crassirostris, mounted Oxford Clay Ophthalmosaurus and Cryptoclidus specimens and numerous Triassic marine reptiles (soooo many nothosaurs, drool). As usual, it was a great social event. There was a lot of beer.

Participants of the 2nd International Workshop on Sauropod Biology and Gigantism. Photo by Philipp Sander, and with thanks to Carole Gee and Martin Sander.

On that note, I think I should stop. Hopefully I’ve given you a good idea of where we’re at with respect to the biology of these most remarkable animals. Substantial areas of confusion and disagreement remain, and I’m sure the next meeting will be equally interesting. If you haven’t been keeping an eye on the many comments (now over 60) that were appended to the part I article, do go and have a look. We ended up talking quite a lot about the whole dinosaur endothermy thing. Again.

For previous Tet Zoo articles on the biology of sauropods and other Mesozoic dinosaurs, please see...

UPDATE: while we’re here... some of you will be aware of the Research Works Act, a vile, nefarious attempt by some academic publishers to RESTRICT ACCESS TO ACADEMIC PUBLICATIONS AS MUCH AS POSSIBLE. We need to act (and act before January 12th) - please read the article here.

Refs - -

Amiot, R., Wang, X., Zhou, Z., Xiaolin Wang, X., Buffetaut, E., Lécuyer, C., Ding, Z., Fluteau, F., Hibino, T., Kusuhashi, N., Mo, J., Suteethorn, V., Yuanqing Wang, Y., Xu, X. & Zhang, F. 2011. Oxygen isotopes of East Asian dinosaurs reveal exceptionally cold Early Cretaceous climates. Proceedings of the National Academy of Sciences 108, 5179-5183.

Eagle, R. A., Tütken, T., Martin, T. S., Tripati, A. K., Fricke, H. C., Connely, M., Cifelli, R. L. & Eiler, J. M. 2011. Dinosaur body temperatures determined from isotopic (C₁₃-O₁₈) ordering in fossil biominerals. Science 333, 443-445.

Farmer, C. G. & Sanders, K. 2010. Unidirectional airflow in the lungs of alligators. Science 327, 338-340.

Hone, D., Naish, D. & Cuthill, I. 2011. Does mutual sexual selection explain the evolution of head crests in pterosaurs and dinosaurs? Lethaia doi:10.1111/j.1502-3931.2011.00300.x

Martin, J., Martin-Rolland, V. & Frey, E. 1998. Not cranes or masts, but beams: the biomechanics of sauropod necks. Oryctos 1, 113-120.

Senter, P. 2007. Necks for sex: sexual selection as an explanation for sauropod dinosaur neck elongation. Journal of Zoology 271, 45-53.

Taylor, M., Hone, D., Wedel, M., & Naish, D. (2011). The long necks of sauropods did not evolve primarily through sexual selection Journal of Zoology, 285 (2), 150-161 DOI: 10.1111/j.1469-7998.2011.00824.x [free pdf]

- ., Wedel, M. J. & Naish, D. 2009. Head and neck posture in sauropod dinosaurs inferred from extant animals. Acta Palaeontologica Polonica 54, 213-220.

Yates, A. M., Wedel, M. J. & Bonnan, M. F. In press. The early evolution of postcranial skeletal pneumaticity in sauropodomorph dinosaurs. Acta Palaeontologica Polonica.

The views expressed are those of the author and are not necessarily those of Scientific American.

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