RE: Rauhut's Thesis

["Rob Gay" <rob_redwing@hotmail.com>]

> Don't you think it is odd that three ceratosaurs outside of the
> Neoceratosaurs have a double crest formed by the same bones and has the
> same form?<
It's interesting, but not necessarily indicitive. And the form isn't exactly
the same, at least in "D." _sinensis_, when the crest is much lower and
placed much closer to the front of the snout (not to mention more robust).

> I can't see this as just convergent.  Usually, convergent characters are
> analogous, not homologous.<
I don't think homology has been demonstrated here.

> That is, they have the same function and may look alike, but they have
> different morphology.<
See above comment for my thoughts on morphology.

> In S. kayentakatae, D. wetherilli, and D. sinensis, the crest is exactly
> the same in how it develops from the cranial bones. So, I think it is not
> convergent.<
Without juvenile cranial material from both of these taxa, we can't say for
sure how it developed. But, the end result was different. "D." _sinensis_
has lower, more forward-placed, robust crests, _D. wetherilli_ has high,
narrow crests that start further back along the skull, and "S."
_kayentakatae_ shows similar crests to _D. wetherilli_, but they are much
more round, and are almost paper thin (this may be a function of size).
Another note on "S." _kayentakatae_:
HP Williams wrote:
> The double-crest of _Syntarsus kayentakatae_ was restored with
_Dilophosaurus_ very much in mind.  AFAIK, no _S. kayentakatae_ specimen
exhibits this type of crest in its entirety; the presence of a dual
nasolacrimal crest in _S. kayentakatae_ was inferred from the structure of
the (incompletely preserved) skull roof in the type specimen<
In Rowe (1989), Tykoski (1998) and a slide shown by Ralph Molnar, the skull
is complete, crushed with the left side raised in relation to the right
side, and with a complete left crest. Rowe states that the right crest was
also present, but was lost during preparation.

> I'm saying I think it is a ceratosaur.  I wouldn't go as far as calling it
> a coelophysoid as in recent cladistic analysis D. wetherilli has fallen
> outside of the Coelophysoidea, and D. sinensis is just plain weird.<
Okay, I get it now ;).
Peace,
Rob

Student of Geology
Northern Arizona University
Biological Science Tech
Manti-La Sal National Forest
AIM: TarryAGoat
http://www.geocities.com/elvisimposter/dinopics.html
http://www.cafepress.com/RobsDinos
"A _Coelophysis_ with feathers?"

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