Did decay or disease give dinos their poses?

8 06 2007

Heilmann's Archaeopteryx

A fantastic drawing of the Berlin specimen of Archaeopteryx, from Gerhard Heilmann’s The Origin of Birds.

Most dinosaurs come out of the ground fragmentary and disjointed; it is always a good day when an articulated skeleton comes out of the ground. Even more spectacular are fossils so incredibly preserved that the impressions of soft parts are clearly visible, perhaps giving us some clues as to what the animal may have looked like in life. Indeed, although such fossils are rare they are well-known, and one of the most peculiar features of theropod dinosaurs is the tendency for the neck to bend backwards and the tail to bend forwards as if the two were trying to touch each other. While, to the best of my understanding, such poses are the result of post-mortem factors like ligaments and other tissues pulling the bones into such a position, a new paper in the journal Paleobiology from Kevin Padian and Cynthia Marshall Faux have a different take on the subject.

Rather than accept taphonomic factors, Padian and Faux argue that the death poses seem to reflect death by disease or asphyxiation, the contorted postures a result of an agonizing death. Even beyond the cause for these postures, Padian and Faux argue that the pose is indicative of animals with high metabolisms (mammals, as well as dinosaurs and pterosaurs, can take the same poses in death), and so they see the idea as being supportive of dynamic and active dinosaurs. In order to show that post-death taphonomic factors didn’t cause the poses, Faux studied some red-tailed hawks that had to be euthanized, and she did not witness the same “death pose” that is so familiar in dinosaurs (nor did she witness it in a horse). Here’s a quote from the Berkley Press Release;

“In horses and smaller animals, rigor mortis sets in within a couple of hours, so I just looked to see if they were moving or not,” Faux said. “And they weren’t moving. They were staying in whatever position I’d left them in. I thought, ‘If birds aren’t doing it, and I’d never observed a horse doing it, then why would dinosaurs be doing it?'”

This is all very interesting, but I’m pretty skeptical. While the most famous fossils articulated in such a manner are found in ash beds or lagoon sedimentary deposits, bigger dinosaurs also seem to reflect this phenomenon (I remember a series of diagrams in John Horner’s The Complete T. rex showing such a skeleton), so arguments about fine-preservation deposits don’t necessarily work. Further, Faux studied two modern birds or prey, related to dinosaurs but with body plans that are quite a bit different than Archaeopteryx or Tyrannosaurus. What the authors should have done (at least in my opinion), is do a taphonomic study of an ostrich as a long-necked, flightless bird would probably be a better analog. Even if they did that, they would have to replicate rapid burial under certain conditions, and such a study would be an entire paper in and of itself.

I don’t want to dismiss their hypothesis out of hand, but I’m not very convinced by what I’ve heard so far (I don’t yet have access to the actual paper). It is important to consider disease in the role of dinosaur life, death, and evolution (something that is often overlooked because the critters are just so interesting themselves), but I’m still inclined to think that the death poses of these dinosaurs took shape after their deaths, even if they did die from disease or asphyxiation. We can study modern animals for clues, but dinosaurs were very different from anything currently alive on the planet, and I think it’s important to take into account both similarities and key differences if we’re going to compare them to modern mammals and birds.

Update: I changed some of the language because I didn’t like my use of the term “drying out.” Likewise, a commenter has asked for some more explanation about the taphonomy of specimen that are in question, so I’m doing some research to post about that (hopefully) later today.

(Hat-tip to Grrlscientist)

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14 responses

8 06 2007
mark

I agree that taphonomic studies of long-necked critters are what’s needed. Particularly, how might the long necks have flopped about after death? If the animal was water-borne for a while, variations in buoyancy would affect final posture, depending on how the body came to rest. After all, how many dinosaurs likely died in their sleep?

8 06 2007
laelaps

Thanks for the input Mark; I would gladly do the research, but alas, I have not the means to do it. In fact I have a whole list of hypotheses/things I want to know, but most of them have to wait until I’m a grad student or get my doctorate. I might have some interesting volunteer work involving some research coming up this summer, but since I don’t know exactly what I’ll be doing or what it’ll end up as, I’m keeping mum on it until I know what I can and can’t say.

8 06 2007
neil

Thanks for blogging on this Brian. I wish I’d known about this paper when Padian came here a few weeks back, I’m eager to read it. I’m holding judgement till I can read the paper, press releases so often misrepresent and overstate conclusions.

Still, I’m inclined to echo your skepticism. It seems that agony would result in an essentially random series of contorted poses, while the same arched neck and tail pose seems to show up again and again (I’m thinking Gorgosaurus etc.).

Maybe our ideas of theropod body posture are just wrong, maybe they walked around staring at the tips of their tails….

11 06 2007
Lars

Thanks for blogging on this. I ran across a news article on this, searched for others in Google news, but it wasn’t until your blog post that I was able to find any sort of reference to the paper where this new hypothesis was published.

While, to the best of my understanding, such poses are the result of the dinosaur’s body drying out, drying tissues stretching the bones,

Assuming you mean the drying tissues pulled on the bones, causing them to be realigned with respect to each other, not actually stretched…
What is the source of your understanding (that such poses are the result of the dinosaur’s body drying out)? Is there positive evidence for drying tissues having that effect? It’s fine to be skeptical of the analogy from modern birds and horses, but why should we be less skeptical of the conventional drying-out hypothesis?

Honest questions from a total non-paleontologist…

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