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Re: Dilong



Rutger Jansma wrote:

Isn't this just logical? I mean...when you reduce the forelimbs before you
increase the relative size of the skull and other changes in the structure
of the skull, you got a theropod can't do anything well.

I'm not so sure it's "logical". Certain other large theropods also show a reduction in relative forelimb length (e.g., carnotaurines and to a lesser extent torvosaurids), as well as certain small theropods (e.g., compsognathids, alvarezsaurids, caudipterygids, _Shanyangosaurus_?). In these cases the reduction in forelimb length may not be correlated with a relative increase in size of the skull. In tyrannosaurids there is biomechanical evidence that the skull took on a greater role in seizing prey at the expense of the forelimbs, which were reduced toward a more limited (but perhaps necessary) function. This evolutionary trajectory is backed up by the morphologies of _Dilong_ and _Eotyrannus_. For other small-armed theropods, the adaptive rationale behind reduction of the forelimbs needs more biomechanical studies, and corroboration from the fossil record.


_Dilong_ also shows that tyrannosaurids had a tridactyl manus *before* the forelimbs were truncated.


Tim