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Re: Archaeopteryx flight
In a message dated 9/4/01 4:37:27 PM EST, z_heraklides@hotmail.com writes:
<< JEEZ JEEZ JEEZ. >>
Here I must agree with Zoe.
Incidentally, I'm not so sure that studying just the bones of the theropod
manus will provide a definitive conclusion about how opposable the various
digits were, how much they could flex, and so forth. (Although >not< studying
the bones certainly won't shed light on the situation!). The attachments and
sizes of the soft parts of the manus (ligaments, forearm muscles, e.g.) are
critically important in determining the actual (as opposed to--sorry about
this pun--the "theoretical," or bone-defined) excursion limits of the digits,
as is the amount of cartilage in the carpus, the flexibility of the forearm,
and so forth.
In the human palm, the first metacarpal is quite mobile relative to the other
metacarpals, which is a major factor in the opposability of the thumb. In
theropods, the short, thick first metacarpal does not seem so mobile, and
most of the pollex opposability probably lay in the phalanges. In Syntarsus
and Dilophosaurus the first metacarpal does seem to lie out of plane with the
other metacarpals, and Galton (1971) argued that the pollex (of Syntarsus)
was therefore opposable to the other digits. In Ceratosaurus, the first
metacarpal was differently shaped, so any opposability might have been more
constrained; I don't think we have a full set of manual phalanges for this
genus. In tetanurans the first metacarpal lies pretty much in the same plane
as the others and the digits radiate more or less uniformly from the carpus,
although the first remains noticeably thicker and stronger. This suggests
that the pollex was no longer opposable--or at least, not nearly as opposable
as in ceratosaurs--although it had some kind of independent functionality
within the hand.
Tough to study this stuff even if you have the specimens in hand (another
%$#@ pun; sorry).