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Re: alvarezsaur fingers



Good thought!

maybe the digit that was anatomically exapted to become the strongest
flexor was retained when the others reduced. I could look into the avian
homologue of FDL - 1. I wonder if it is the flexor carpi ulnaris caudalis.



> 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
>>
>>
>


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