RE: Rauhut's Thesis (long)

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

>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?

Now Im really confused.  Your saying that Monolophosaurus' crest is a direct
descendent of ceratosaur cranial ornamentation?

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?

Across a large group of birds, structures such as this and cranial
ornamentation are not useful, but, it is obviously useful to say that webbed
feet is one of the characters of ducks.  Therefore, double nasolacrimal crests
*might* be a feature of non-neoceratosaurian ceratosaurs (boy, that was a
mouthful!).

How you can confidently draw all those characters from a small illustration in
the paper on "D." sinensis, I don't know. I'd like to see someone do a
cladistic analysis to see where *sinensis* falls.  I do have a question, the
authors state that "D." sinensis has 5 premax. teeth, are there any theropod
groups that have this as well?

Regards,
Randall Irmis

>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?"
>
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