RE: Rauhut's Thesis

[rbi <rbi@dana.ucc.nau.edu>]

<<such cranial specializations are horribly subject to environmental
pressures, and not gene flow. Holtz has recently expounded on this.>>

In a paper, or on list?

<<Several theropods have cranial crests forms from the lateral edges of the
maxillae and nasals, including *Syntarsus kayentakatae*, *Dilophosaurus
wetherilli*, *"D." sinensis*>>

And they are all ceratosaurs, either coelophysoids or sister taxa to the
Coelophysoidea.  Plus, the formation and morphology of the crest is almost
identical. I have a hard time believing that this is convergence.

<<comparatively, *Cryolophosaurus ellioti* bears ridges from the nasals and
maxillae that join into the mildly transverse crests>>

And again, this taxon is not a ceratosaur, and has a different crest form.
Cranial ornamentation is not useful in phylogeny when comparing distantly
related taxa with ornamentation that is morphologically different.  However,
when you have three taxa that are closely related with identical
ornamentation, that is completely different.

<<*Coelophysis bauri* and *Syntarsus rhodesiensis* have raised lateral edges
of the nasals/maxillae that are probably plastically deformed into the
crest.>>

And I follow Downs (2000) synonymization of S. rhodesiensis with the genus
Coelophysis.  Therefore, these "ridges" are probably homologous.

<<Nothing lead this into genetics.>>

It was just a possible explanation, I was offering it foreward as a
*possibility*.

<<To say that having paired cranial crests makes this dilophosaurine-looking
skull in the light of several tetanurine features, such as position of the
maxillary tooth row, form of the suspensorium, and several postcranial
features, a ceratosaur, is to ignore the data but to pick and choose whichever
one character that you feels has more weight.>>

<<I am interested in you supporting features for it being a ceratosaur.>>

I repeat that I "think" it is a ceratosaur, although I am not sure that is the
same genus as D. wetherilli.  If a detailed study and phylogenetic analysis
proves me wrong, then thats how science works.  Unfortunately, the description
was relatively brief and lacking many figures.  I do not have the paper handy
right now, so I cannot give you specific characters.  I would like to see
"Dilophosaurus" sinensis incorporated into a cladistic analysis to know
whether the ceratosaur characters are overwhelmed by the tetanurine
characters. Also, I caution that interpreting characters from a drawn figure
is very unreliable.

Regards,
Randall Irmis