[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Reversed Hallux in Theropods: a query



In a message dated 95-11-25 08:40:03 EST, ornstn@inforamp.net (Ronald
Orenstein) writes:

>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.

Fair enough. However, I have yet to encounter in the literature a compelling
function for the retroverted hallux that does not involve perching. Either it
evolved for that function, or it evolved for some other function that nobody
has been able to figure out yet. I suppose the feature could have evolved as
an aid for walking on lily pads (an example from your earlier postings), but
that strikes me as less likely, because the presence of lily pads in the
environment for the millions of years it would take for a hallux to retrovert
is improbable. Most likely, the lily-pad adaptation occurred because the
retroverted hallux was already present, and all it had to do was grow a
little bigger and change its shape a little.

Incidentally, don't evolutionary theorists have some kind of specialized
vocabulary to describe a "forced" adaptation, an "opportunistic" adaptation,
and so forth?