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Re: More on therizinosaurs



In a message dated 96-12-12 11:47:16 EST, gpb6845@msu.oscs.montana.edu
writes:

>  Perhaps the similarity to prosauropod feet has to do with reverting
> to a Herrerasaur style foot and then getting heavier (Alxasaurus,
> although small, is still a great deal larger than Herrerasaurus)
> making their feet more similar to those of bigger prosauropods.

But in _Tyrannosaurus_ and the giant theropods, which outweighed _Alxasaurus_
by a couple of orders of magnitude, we still have the usual three-toed
theropod feet. Sorry--the "weight-gain argument" for reacquiring a
prosauropod-like foot in segnosaurs just doesn't wash. Segnosaur feet
resemble prosauropod feet, right down to the tarsal counts, by homology, not
by homoplasy.

[ Re-read his message, George.  He didn't suggest that weight gain was
  the cause of the proposed homoplasy (at least not without being
  combined with the prior -- admittedly completely speculative --
  reversion). -- MR ]