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Re: thoughts on Dinocephalosaurus (long)



At 3:04 PM +0200 9/24/04, silvio.renesto wrote:
3) In the article quoted by Dan Varner, it is written that protorosaurs lie in the the ancestry of dinosaurs. Surely they are closer than synapsids, but, it seems to me that there is some agreement that they could be the sister group of archosaurs as a whole, thus this claim of ancestry is a bit excessive, perhaps without the word dinosaur no one will pay attention to anything? mah...

All too many news reports simply called Dinocephalosaurus a dinosaur in the headline.


The Science paper is a one-page "Brevia" which goes into little detail. As best I could find out, protorosaurs are usually considered a sister group of the basal archosaurs, but there is considerable uncertainty about the phylogeny. At this stage I'd say the relationships remain to be determined. Protorosaurs deserve considerably more work to sort out their possible relationships to plesiosaurs, pterosaurs, and other archosaurs. The authors noted a strong similarity to plesiosaurs in Dinocephalosaurus, but attribute it to convergent evolution.

4) In the article quoted by Jeff Hecht there is a comparison with Tanystropheus neck and, if I read correctly, it is written that the neck of Tanystropheus is about half the length of that of Dinocephalosaurus. Nope. Big specimens of Tanystropheus have a neck as long as or even longer than that of Dinocephalosaurus both as absolute size and also proportionally. It is true that the number of cervical vertebrae in Tanystropheus is roughly one half that of Dinocephalosaurus, but each vertebra is much longer, as correctly pointed out in the original paper in Science.

I spoke to a couple of the authors, but I could have misinterpreted what they said.



5) The limbs of Dinocephalosaurus are more paddle like than those of Tanystropheus, and carpal and especially tarsal bones look like those of most nothosaurs: simple rounded bones; In comparison, the tarsus of Tanystropheus, with its tightly packed bones is much more terrestrial-like. As authors noticed in the paper in Science, despite the similarity Dinocephalosaurus is not strictly related to Tanystropheus, but it seems an offshot from a more basal stock of protorosaurs and the elongate neck was acquired independently. Perhaps the long neck served different purposes in the two taxa which may have lived in (slightly?) different environments.

From what I was told, Tanystropheus was probably semi-aquatic. The long neck would have been VERY cumbersome on land. I hope to hear more about these guys.



-- Jeff Hecht, science & technology writer jeff@jeffhecht.com; http://www.jeffhecht.com Boston Correspondent: New Scientist magazine Contributing Editor: Laser Focus World 525 Auburn St., Auburndale, MA 02466 USA v. 617-965-3834; fax 617-332-4760