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Re: Catch-22



Don Ohmes <d_ohmes@yahoo.com> wrote:


> Note also the position of the claw on the ankle. Not a perfect analogy to
> the partially retroverted hallux though...


In this context, Bock and Miller (1959) regarded the best pedal
configuration for vertical trunk-climbing in birds to be
pamprodactyly: all four toes cranially (forwardly) directed.


> So your task is to show that there is no functional conflict between a
> climbing pes and a running pes. Restated -- it seems to me that you must
> show that an incremental change in the optimized basal running pes can
> improve climbing talents significantly w/out diluting running talents even a
> little.


I'm not convinced that all primitively flightless theropods
necessarily had to be good runners.  See below...


> I see Tim's argument that turkeys (American-style) demonstrate a no-conflict
> compromise solution as weak -- temporarily flight-less turkeys can be caught
> by even a normal human, and the ostrich pes shows little or no sign of it's
> perching past.


I would contend that the "long" hallux is *not* to blame for turkeys
being somewhat slow on the ground.  It probably has more to do with
the lack of cursorial proportions in the hindlimb.


You're also assuming that all theropods needed to be highly cursorial.
 The flightless, chicken-sized Cretaceous bird _Patagopteryx_ had weak
cursorial proportions, and a fairly robust and descended hallux.


As for the ostrich, it is a specialized cursorial biped, with only two
toes per foot.  Most cursorial ratites have three toes - as do
ornithomimids, which were among the most cursorial of Cretaceous
theropods.






Cheers

Tim