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Re: Maniraptor arms?



On Friday, May 11, 2007, at 10:30  PM, Anthony Docimo wrote:


When a maniraptoran moved its arm, did the two arms move in sync with one another, each a mirror image of the other? (since it likely wasn't in sync with the legs, as quadrapeds are)



I got the idea for this question by thinking of how birds fly by flapping their wings largely in sync with one anther -- opposed to how a primate can hang by one arm, while eating with the other.



thoughts?

Well, I'm not sure how one would test for arm motion timing, but I would hypothesize that the arms were kept folded during walking/running and therefore did not move much at all as a product of locomotion (*). Whether the arms were used in synchrony or out of phase when grabbing for prey, obstacles, etc. would seem to matter primarily on what the animals were deploying the arms to do. A predatory stroke would, for example, probably be synchronous against small prey (grabbing) and asynchronous when utilized to harm larger animals (slashing blows).


Birds actually do not always deploy their wings in synchrony. They flap in synchrony under the most common conditions (leaping launches, level cruising flight, etc) but asynchronous flapping is seen during evasive maneuvers as well as some launching dynamics (namely large anseriform birds).

*The exception to the locomotion comment would be in maniraptorans with forelimbs capable of generating aerodynamic forces, in which case they could be deployed during very maneuvers, with the synchrony or lack thereof depending on the maneuver in question (example: leaps probably near synchrony, banking likely highly asynchronous or synchronous with asymmetrically deployment).


Cheers,

--Mike H.