Re: Coelurosaur ischium unique?

["Steve Brusatte" <dinoland@lycos.com>]

On Wed, 19 Dec 2001 23:49:43  
 Mickey_Mortimer11 wrote:
>Ken Kinman wrote-
>
>>     Does the coelurosaur ischium always possess at least two of the
>> following three features?   Each of these features is occasionally lacking
>> in a few coelurosaurs, but I believe that all coelurosaurs have at least
>two
>> of the three (and most would have all three):
>>      Ischium (1) reduced to less than 2/3 length of the pubis; (2) lacking
>> an ischial foot; and (3) possessing a prominent, triangular obturator
>> process (placed more than 25% down the ischial shaft).
>
>Ornithomimids and Compsognathus have 3 but not 1 or 2.  Scipionyx lacks at
>least 1 and 2.  Sinosauropteryx lacks all of them.  Many ornithothoracines
>will lack 1 and 3, but still have 2.

Sure, but how well would these characters in regards to Scipionyx hold up?  The 
only known specimen is a juvenile, and any one of these characters could have 
changed as the animal went through ontogeny.  A simple peramorphic shift in the 
development of the ischium could have fiddled with its length in regards to the 
pubis.  The same could also be true of the triangular obturator, although I 
don't know when/how it forms or changes with ontogeny (hopefully Rauhut's paper 
will give some data).  

Of course, Mateus et al. found some startling resemblances between the bones 
(femora?) of mature members of the genus Lourinhanosaurus and embryos found 
nearby.  Despite these characters, Mateus didn't ascribe these embryos to 
Lourinhanosaurus, although I believe the paper says such an ascription is 
probably accurate.  Judging by this model, many characters in the femur (I 
believe) do develop at a very early stage, often before birth.  Of course, 
Lourinhanosaurus has been reconstructed as an allosauroid, which Scipionyx 
certainly is not.  Hopefully Cristiano Dal Sasso's new book will give new 
details on the phylogenetic position of Scipionyx, which, if rumor is correct, 
I have heard it does.

Steve

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