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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?
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
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