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Re: Thecodont questions



Larry Dunn wrote:

> Thecodonts.  Those guys leave me scratching my head sometimes.  Like 
> now.
> 
> 1) Why did Postosuchus k. have that massive supraorbital ridge?  Has 
> anyone hypothesized yet?  This wasn't typical of Rauisuchids, was it? 
> If not, why did  P. develop these?

Chatterjee's Postosuchus kirkpatricki skull reconstruction indeed 
shows a rugose ridge over the entire length of the skull roof, which 
is not present in other rauisuchid reconstructions (e.g. Ticinosuchus 
and Saurosuchus) (there is currently quite some discussion whether 
Postosuchus is a 'true rauisuchid' or a poposaurid). However as far 
as I know there is (apart from Postosuchus) not a complete rauisuchid 
skull known, and all published figures are extensively reconstructed, 
so to give an answer one should best look at the original material.
Perhaps some professional on this list can give a more accurate 
answer??  
As far as the function of this ridge concerns, I haven't read 
anything about it but I'd suppose (speculation of course) it was the 
same of the cranial ornaments in e.g. neoceratosaurs, allosaurs and 
tyrannosaurs:
intraspecific display.


> 2) How are the forelimbs of Desmatosuchus best described (choose 
> one):
> 
> -a bit longer than hindlimbs
> -same length as hindlimbs
> -a bit shorter than hindlimbs
> -much shorter than hindlimbs

In Desmatosuchus haplocerus, the best known D. species, the forelimbs 
seem to be about half as long as the hindlimbs, and quite more 
gracile, the animal however undoubtedly being an obligate quadruped. 
In Long and Murry's 'Carnian and Norian tetrapods from the 
American Southwest' a figured humerus measures about 25cm, the femur 
about 40cm. In the same volume a figured reconstruction of D. has 
about the same limb proportions as in the well known 'Stagonolepis 
reconstruction' which you find in every handbook. 
However, I seem to remember Chatterjee mentioned a new, highly 
derived Desmatosuchus species found in the Dockum near Post (Texas) 
which he tentatively attributed a facultative bipedal posture (in 
Padian's 'The beginning of the Age of Dinosaurs'); I haven't heard 
anything more of this unfortunately, maybe someone else has.

Pieter Depuydt