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RE: the maniraptoran wrist



Greg Paul wrote: 

> As I detail in Dinosaurs of the Air, the avepectoran wrist and folding
> arm evolved in order to fold wings among fliers, and was retained in 
> neoflightless forms as they often are in neoflightless birds. The idea
> that such arms evolved as snap action prey catching systems is weak 
> since such devices evolve only in sit-and-wait predators, not those 
> that can run fast enough to catch prey on the move and simpy reach out 
> with the arms to latch on. 

I'll start of by saying that I though DA was a wonderful piece of scientific
writing - I highly recommend it. 

But... the argument outlined by GSP above didn't hook me.  I can conceive of
two counterarguments:

(1) Maybe maniraptorans were indeed as sit-and-wait predators - or at least
began as such.  Judging from their hindlimb proportins, the cursorial
abilities of many non-avian maniraptorans may not have been too impressive.
This suggests a reliance on ambush attacks and/or short (rather than
protracted) pursuits where maneuverability was at least as important as
speed.  This leads on to the second point...

(2) There is an alternative hypothesis that the folding mechanism of the
arms was designed to reduce rotational inertia during such predatory
pursuits. (I've mentioned the paper on this list, but can't recall the
auhors at the moment.)  As such, tucking the arms against the chest improved
maneuverability - which might be regarded as useful to predators that relied
on brief chases to run down prey.  The maniraptoran forelimbs were deployed
only when the prey was within reach - but during the chase the long, gangly
forelimbs were kept out of the way.



Tim