June 1, 2009
The Sauropod Posture Debate, Part Eleventy
A herd of Diplodocus with their necks in a raised posture, by Mark Witton.
Did the long-necked sauropod dinosaurs hold their necks high in the air or low to the ground? If you think this is a question easily answered, you are sorely mistaken. In many ways sauropods were unlike any living creatures, and scientists have been debating their posture for years. Indeed, last month a short communication in Science suggested that the ancient giants held their heads low to the ground, but a new paper published in Acta Palaeontologica Polonica by Mike Taylor, Matt Wedel, and Darren Naish (who are also behind the SV-POW! blog) suggests that these dinosaurs regularly held their heads high.
A large part of the current debate has to do with the different ways of approaching the problem. You can study the bones of dinosaurs to get an idea of their posture, but they also would have required physiological mechanisms to do things like maintain blood pressure. A scientist who bases his or her hypothesis on skeletal anatomy may reach a very different conclusion than one who tries to reconstruct sauropod physiology. The authors of the new paper decided to look at the skeletal evidence and compared the necks of sauropods to many kinds of living vertebrates to see if the way living animals hold their necks could answer some questions about sauropods.
When they looked at the neck posture of birds, rabbits, cats, rodents, and primates, the team found that these animals typically held their necks vertically and that the middle part of the neck was relatively rigid. They also found that the living animals often had more flexibility in their necks than you would think just looking at bones alone. More striking, though, was that the animals studied, including the closest living relatives to dinosaurs (birds and crocodylians), held their necks up, not down. If almost all other land-dwelling vertebrates were doing it, there is a good chance sauropods were doing it, too. From what they found, the scientists strongly suggest that not only did sauropods hold their necks above a horizontal position, but they had a much wider range of motion than other scientists have suggested.
I have no doubt that the posture of sauropods will continue to be debated, especially in terms of physiology and feeding, but this paper is a very important contribution to the discussion. As the authors state, unless they were unlike almost all groups of terrestrial vertebrates, sauropods were “holding their heads high.” For more be sure to check out the summaries of the paper at Tetrapod Zoology and SV-POW!, written by some of the authors of the study.
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3 Comments »
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Brian,
I just came across your contribution to the sauropod neck debate.
There should not be a dichotomy between anatomy and physiology to understand whether or not sauropods could raise their heads. Of course one needs both. If either anatomy or physiology would prevent raising of the head, then the animals couldn’t do it.
The paper by Taylor et al. is based on neck positions in living animals, all of which are small. Because the problem of blood pressure and the energy required to maintain it depends on the absolute vertical distance above the heart, looking at small animals is pointless. But one immediately sees that the giraffe has blood pressure problems with a 2 meter neck. For a vertical 9 m neck, the problem becomes prohibitive in my view.
It is telling that Taylor et al. not only did not solve the blood pressure problem, they didn’t even mention that it exists, although they corresponded with me before publication.
Anyone is free to invent solutions to the sauropod problem that do not exist in living animals, but so far, in 35 years since I first mentioned this problem, no one has satisfactorily solved it. Usually, it is simply ignored or stated to be a curious unsolvable paradox, so strong is the need to keep the sauropod heads in the trees.
VERY belatedly, as I’ve just noticed Roger’s comment …
It’s true that we didn’t mention the blood pressure issue at all in the 2009 paper. But that’s not because we don’t have any answers; it’s because we’re keeping our powder dry for a separate publication, currently in prep.
(To clarify: in saying that, I am not claiming to have a bulletproof rebuttal of Roger’s position, only that we have some ideas which, when we’ve worked them through, should provide a credible counterpoint. Until we’ve done the work, we won’t know ourselves how strong our counter-argument is.)