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Reversed Hallux



<<Date: Sun, 16 May 1999 15:57:06 -0500
From: "Matthew Bonnan" <Z966341@wpo.cso.niu.edu>
To: <bh162@scn.org>, <dinosaur@usc.edu>
Subject: Re: Gatesy et al.'s footprint paper (excerpts)
Message-ID: <s73eeae7.076@wpo.cso.niu.edu>

Phil:

You said: "All in all, I was quite intrigued by the team's
conclusions.  It seems
that researchers now need to rethink the whole issue of the evolution
of
the theropodan hallux with a bit more care.  When *did* the hallux
reverse?  Maybe it was in the trees after all.  Padian *still*
maintains
that Archaeopteryx was not much of a percher (in spite of possessing
a
fully reversed hallux), and that true perching came later  (to quote
Kevin from _Nature_:>

"For instance, in Archaeopteryx, which is the first known bird, the
first toe is fully opposable (that is, it faces the other digits on
the
same foot), and in later birds the claws enlarge for perching,
suggesting the start of true arboreality." - Kevin Padian."

>From what I've seen in photographs of Archaeopteryx, although it does
appear to have a reversed hallux, the location of this toe is located
closer to the ankle joint than that of modern perchers where the
hallux is close to or in line with the rest of foot.  I suspect that
is why Kevin Padian and others have been reluctant to grant
Archaeopteryx the powers of perching, because you'd really have to
rock the ankle quite a bit back to get the hallux close to a branch.

But, I'm no expert, so fire away.>>


Pardon me "interrupting" this thread. And I wasn`t intending to start
another arguement so soon, but as long as this subject is being brought
up,....Dosen`t it seem unlikely that Theropod dinosaurs, with their halluxes
(hallucies??) located high up towards the ankle had evolved "toward" the
state of a lowered hallux suitable for perching??

I mean reptiles started with all the toes in pretty much the same plane. I
can see them lose digit five and begin to reverse digit one for the purpose
of better grip and perching on tree branches, and later loosing this
function on the ground, the hallux rising (through natural selection)
perhaps to be "out of the way" for a cursorial mode. I can`t see ecological
reasons for a hallux to descend, especially to reverse and descend while the
beasts were already on the ground, to evolve into the ideal perching state.
I just can`t see the natural forces involved in this scenario.

Sorry if this has also been "discussed to death" before. I know it is a
"bone of contention" to those argueing for a trees down development. (Just
add it to the list of points I`ve been making to explain why I think BCF is
how it happened).