RE: Rauhut's Thesis (long)

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

> AAHHHH!!!  Your missing my point.<
Just the same as I think you're missing mine.

> First, that differences are to be expected between species and genera,
> therefore I am not surprised by the differences in D. wetherilli and "D."
> sinensis. The point about Monolophosaurus is that it IS different, and
> therefore is a clear example of convergence, whereas the two species of
> Dilophosaurus are not.<
My point is that _Monolophosaurus_ is _not_ convergent, it's a different
structure. Tyrannosaurids have display structures formed from the nasal and
lacrimal, does that mean that they're closely related? To restate
_Monolophosaurus_ has a singular ridge, which is not at all analogous to the
paired nasolacrimal crests seen in these specimens. According to the article
mentioned onlist about flamingos, identical structures can be the result of
convergence based on selective pressures. With the differences in the crests
seen in _D. wetherilli_ and "D." _sinensis_, and the potentially tetanuran
status of "D." _sinensis_, why should one assume that these crests are the
same structure?

To restate the differeneces I see in the skull and mandible:
_Dilophosaurus wetherilli_
Premaxilla very elongate and low, with the crest not projecting over it.
Nasal fenestra elongate and low, set far back in the premaxilla
Sharp hooking between the premaxilla and maxilla
Teeth slightly hooked, narrow and elongate
Antorbital fenestra set high above ventral margin of skull and positioned
caudaly in the maxilla
Antorbital fenestra triangular in shape, and low, somewhat small
Large, caudally offset antorbital platform
Pronounced ventral bowing of the jugal
Orbit narrow and slanted caudally
Medialy constricted lateral temporal fenestra
Crests high, thin, some vertical ornamentation, caudally placed
Angular reduced
External mandibular fenestra reduced and situated more ventral
Medial constriction of the dentary
Surrangular enlarged and elongate

"Dilophosaurus" _sinensis_
Premaxilla high and short, with the crest projecting over it.
Nasal fenestra elongate and high, set forward in the premaxilla
Hooking between the premaxilla and maxilla not very pronounced
Teeth broad and short
Antorbital fenestra positioned medially in the maxilla
Antorbital fenestra triangular in shape, but with a pronounced bowing on the
dorsal surface, tall
Small, proximally offset antorbital platform
Jugal nearly flat
Orbit large and vertical, teardrop shaped
Ventrally expanded lateral temporal fenestra
Crests short, thick, no vertical ornamentation, proximally placed,
dorsolateral bowing
Angular enlarged
External mandibular fenestra enlarged and situated dorsally
Medial expansion of the dentary
Surrangular reduced and short

These bespeak of no real close relationship, and in light of that, it would
be logical to state that the crests were likely convergent.

> We can go on arguing this forever, but that is useless.<
I concur. We should probably take this offlist, since I'm sure we're boring
people with our debate.

> What I am putting forth is just a hypothesis, that is all.<
It seems untestable at the moment.

> I think nothing can be settled until a detailed description of
> "Dilophosaurus" sinensis is done, and we all can at the very least examine
> accurate illustrations and photos of the whole skeleton and individual
> cranial elements.<
This is probably also true...
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?"

_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com