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Re: alvarezsaur fingers



In Crocodylians at least there is a large digital plantarflexor mainly
associated with Digit 1 (the FDL-1, which to some extent is also
attached to the main digital flexor tendon of FDL-2, but definitely
sends a discrete tendon to the first digit - pers obs, but see Meers
2003, 'crocodylian forelimb musculature and its relevance to
Archosauria'), that is roughly equivalent in mass to the main flexor
for all the other digits.  In theory that would favour the pollux with
a greater degree of individual control and ability to exert forces in
isolation to the other digits, which all share their major
plantarflexor. I dunno if that's the case with birds (I'm not familiar
with their forelimb anatomy), but based on crocodylians, the pollux in
archosaurs may have already been functionally distinct to some degree.
Maybe a reason to keep that one and not the others?

On 13 May 2011 21:26, Jason Brougham <jaseb@amnh.org> wrote:
> We had wide ranging discussions about alvarezsaur biology on these threads:
>
> Re: dino-lice
> Re: Alvarezsaur spurs (was Re: dino-lice)
>
> but I wonder if anyone discussed the transition of the major finger in
> alvarezsauroids from finger II to finger I. Haplocheirus has the standard
> maniraptoran plan, with a large, robust, second finger. By the time we get
> to Mononykus digit I is broad and robust, while II is just a vestige.
>
> Anyone care to speculate on functional hypotheses that explain that?
>
> The only thing that comes to mind is the hand of avialans, where finger II
> is largest but supports the wing feathers, so finger I is the one that we
> would expect to function in quadrupedal climbing. If alvarezsaurs had
> large wings in their ancestry, but then went on to specialize in a
> terrestrial habit and myrmecophagy, I can see how digit I might take over
> with tearing into bark or rotten wood, and then digit II might be free to
> reduce as the wings were reduced. But alvarezsaurs are usually recovered
> way lower in the cladogram than where we might expect arboreality and/or
> large wings.
>
> Any thoughts?
>
> Jason Brougham
> Senior Principal Preparator
> Department of Exhibition
> American Museum of Natural History
> 81st Street at Central Park West
> 212 496 3544
> jaseb@amnh.org
>
>