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RE: Tyrannosaurids, skippy, and sterna

On Tue, 9 Jul 2002 15:38:20   
 HPB1956 wrote:
>Thomas R. Holtz wrote on 07/082002:
>> To update folks: forget everything you've known about the sternum in 
>tyrannosaurids and Scipionyx.
>> In NEITHER case is the element(s) identified really the sternum.
>Doesn't surprise me in the case of Scipionyx. It's a juvenile and it's 
>sternum may have later ossified while reaching adulthood.
>It juvenile characters may also lead to a basal phylogenetic position in 
>cladistic analysis. To cite from DA by Gregory S. Paul:
>The juvenile status of wee Scipionyx - it may have just emerged from the egg 
>- hinders analysis of it's phylogenetic position:
>some of it's attributes may be features of youth and may have later been 
>modified during growth. In particular, the low position of the superior 
>temporal bar may be due to the large size of the juvenile braincase. The long 
>arms may be a juvenile arboreal adaption. Conversely, it is possible that 
>birdlike features developed only with maturity.

Very true...but, we must not use immaturity as a sweeping "excuse."  Ricqles, 
Mateus, Antunes, and Taquet have shown that bone-specific anatomical details 
are actually present in embryos that are most likely _Lourinhanosaurus_.  Many 
characters are most definitely affected by ontogeny, but not all.  
Unfortunately, it's difficult to determine which are which, because who's to 
say that the pattern found in the Portuguese embryos is similar to that in 
other theropods?


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