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Re: PAMPRODACTLY IN APTERYX



In a message dated 98-08-25 22:24:03 EDT, m_troutman@hotmail.com writes:

<<  All known theropod feet preserved show conclusively that the halluces were
not reversed (Norell and Makovicky 1997; Amer. Mus. Novitates 3215). >>


This is wrong, because the hallux seldom shows in theropod tracks (it was held
well off the ground when they walked on a normal substrate). If the hallux
>doesn't show< in the tracks, how can anyone tell where it was in the
foot-->from< the tracks? Let alone >conclusively<!? When the hallux >does<
show in theropod tracks, it is almost invariably at the back of the foot, or
at best, at the side of the foot pointing inward and backward at least at a
right angle to the axis of the foot. There's a very nice cast of a
tyrannosaurid track at the San Diego Natural History Museum that shows a
hallux impression, and it is at the >back< of the foot.

Certainly in theropods adapted to a cursorial lifestyle a fully retroverted
and enlarged hallux of the kind seen in many flying birds would be a
hindrance. There's no reason to expect them to retain an ancestrally
retroverted hallux under these circumstances. In view of the massive amount of
similar, convergent hallux reduction in secondarily flightless birds, it is
>way< premature to insist that the theropod hallux was not modified from an
ancestral retroverted configuration or not retroverted itself.

The hallux was not closely articulated with the other foot bones in any
theropod, and it could move quite a bit--from the side, where it could align
with the other metatarsals, to the back, where it could oppose the other toes.
Your own thumb exhibits roughly the same range of movement. The entire design
of any theropod foot suggests descent from a form in which the hallux had been
opposable to the other toes and had some kind of perching function.

Jerry Harris described some four-toed ?theropod tracks recently, but since
this kind of foot is unknown in skeletal remains of theropods, the tracks are
difficult to classify. Who knows what they are.