A Dimetrodon with a funky sail

Last week I spent some time writing about Dimetrodon and the various functions paleontologists ascribed to its sail (from a literal sail to a sign of coming extinction). It can be easy to forget that no two sails were exactly alike, though, and paleo-artist Michael Skrepnick (see my interview with him here) was kind enough to remind me of a rather spectacular example of this point.

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Two views of a Dimetrodon gigashomogenes with a pathological sail. Courtesy of Michael Skrepnick.

Just like any other bones the osteological supports for the sail of Dimetrodon would have been subject to injury and disease. This was the case with a particular specimen of Dimetrodon gigashomogenes described by Stuart Sumida and Elizabeth Rega and restored by Skrepnick. (You can see Rega's .ppt presentation on the specimen here.) Apparently this individual had suffered some injury earlier in life that caused some of the spines supporting the sail to break. When the bones healed they did not retain their "normal" position. Instead they twisted and bent forward.

Lots of books on paleontology feature somewhat idealized versions of extinct animals, but I love learning about cases like this. It drives home the fact that fossils are the extant remains of once-living creatures which exhibited variation and are not just funny-shaped rocks. It is one thing to look at a fossil skeleton and appreciate it in its present state. It is quite another to study it in detail to understand the life of that particular animal.

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Aside from the odd pathology, that's a wonderful picture by Michael, as usual. I don't think I've ever seen a pelycosaur out of him...

Just to elaborate, the pathologies occur along several anterior dorsals, proximally on the spines (close to the centrum )and rehealing / exostosis on the bone surface is evident ( musta hurt ! )... HOWEVER conversely and IN ADDITION to the injuries, the distal ends of many of the spines throughout the entire sail series are bent and twisted ALOT, and because of their arrangement relative to each other, as the specimen was originally discovered in situ, this peculiar deformation in spine morphology is not an artefact of postdepositional / geological forces at work, but rather seems to have been "natural" to the animal in life.

Whereas many specimens of Dimetrodon have relatively conservative, orderly sail spine arrangements (although some seem to show some a bit of warp that might be ordinarily discounted to crushing / bending postmortem) this individual shows that there may have been an interesting variation of "displays" in these sails, not previously considered. . .

By Mike Skrepnick (not verified) on 25 Mar 2009 #permalink

I'm glad modern science can now pick out pathologies (as well as sexual, individual, and age-related differences) in fossils. At one time, a pathology like the above-mentioned would have had paleontologists rushing to name a new species!

By Raymond Minton (not verified) on 26 Mar 2009 #permalink

There are SO many examples of paleontologists finding one bone and reconstructing an entire bizarre animal from it. I'm glad to see that we know a little bit more about Dimetrodons, since they are so neat.

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Thanks! You have an awesome blog.

Brian Switek

dimetrodon can not stand up biped. what is your opinion? what is your reasons for your answer?

Amin Khaleghparast (from IRAN)

please answer to my question.
please send to my email your valuable answers and reasons.