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RE: Triassic dinosaur evolution

Eric Boehm wrote:

> Generically, I would think a quadrupedal predator would be able to grow
> larger than a Biped, and given the limbs of a T-rex, its obvious freeing the
> forelimbs was not a major factor in the effectiveness of a biped predator.

Whoah!  Hang on there.  The forelimbs of T. rex were not a major factor in the 
effectiveness of *that particular* bipedal predator.  But there's plenty of 
non-avian theropods (of all sizes) in which the forelimbs were quite large, and 
presumably put to good use in predation (or bad use, if you happen to be the 
prey).  Not that I'm saying that T. rex didn't use its forelimbs in predation; 
it's just that it didn't use them to catch prey.  Some big allosauroids and 
"megalosaur"-grade theropods had very powerful forelimbs; even though some of 
the latter (like _Torvosaurus_) had forelimbs that were quite short, they were 
also very robust.  

The use of the forelimbs in prey capture could be seen as extremely important 
to dinosaurs, as a major factor in the shift to bipedality by the first 
dinosaurs (or their immediate ancestors).  This prey-catching function was 
retained by most theropod lineages - although not all, because some did 
drastically reduce the size of the forelimbs (tyrannosaurids, _Giganotosaurus_, 
 carnotaurines, alvarezsaurs, compsognathids), and/or used them for something 
else (alvarezsaurids, ornithomimosaurs,  therizinosauroids, birds).  The 
tyrannosaurid strategy for prey capture allowed the forelimbs to shrink, and 
take on an auxilliary role to the jaws.  But that's just the way that 
tyrannosaurids did things.  Overall, the forelimbs of theropods played an 
important role in predation.   



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