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Re: Reversed Hallux in Theropods: a query



>Umm--flying birds are hardly obligatorily ground-dwelling, cursorial bipeds.
>They are not obliged to place their feet on the ground and walk for most of
>their lives.

Perhaps not - but the species I referred to do not perch either (some live
in treeless areas) and I cannot imagine how a large hallux aids flight, or
why some larks and others should have evolved an enlarged (if elongate)
hallucal claw along with a terrestrial habit (rather than a reduced one) if
it had no function.  Admittedly we are talking about pretty small critters
here, of course.

 And the retroverted hallux is not _necessary_ for perching, of
>course, merely a quite convenient adaptation for it that arose in the lineage
>that led to birds. The problem is to account for the presence of the
>retroverted hallux in so many different theropod lineages, not to figure out
>all the different things all the different birds of the world can do with
>their feet.

But if you do not understand the range of functions to which a retroverted
hallux may be put in those living birds that have one, you may very well err
in figuring out why therapods had one.  If you assume that the only
evolutionary reason for such  a structure to evolve is to assist in
perching, then you will of course conclude that therapods went through a
perching stage at some point in their evolution.  If, however, you can
demonstrate that such a digit could serve another function or functions (and
examining living birds is at least one way to do so) such a conclusion
becomes far less definite.
--
Ronald I. Orenstein                           Phone: (905) 820-7886 (home)
International Wildlife Coalition              Fax/Modem: (905) 569-0116 (home)
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