Re: thoughts on Dinocephalosaurus (long)

[Jeff Hecht <jeff@jeffhecht.com>]

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
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