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Re: Microraptor Wings

Jason Brougham <jaseb@amnh.org> wrote:

> My blog posting grows from online correspondence that Dr. David Hone and I
> have had. It draws on his thought - provoking blog postings about
> Microraptor's super - long primary feathers and how the constrain the use
> of the hands for predatory strikes.

The other problem for any dromaeosaurid, as noted by Senter (2006), is
the obligatory supination of the manus during wrist extension.  This
meant that the palms and the tips of the unguals were oriented away
from the ground when the wrist was extended - so a scooping motion
would be required to bring the prey up to the chest.  Long feathers
would prevent the two hands from working together, because the wings
(pennibrachia) would collide with one another.  So small prey could
only be clutched with one hand against the chest, Napolean
Bonaparte-style.  For _Velociraptor_ and friends, two-handed grasping
of large prey fits with its inferred ecology.  But it doesn't hold for
the smaller paravians, like _Microraptor_, which presumably targeted
small prey.  Although I suppose it could work against a pterosaur
during take-off.  (I once had a wild idea that microraptorines could
have targeted sauropods, and gripped the neck with both arms either to
deliver a pesky bite, or to pick off arthropod parasites.)

The fact is, the typical theropod manus was not adapted for grasping
small objects anyway, on account of the divergence of the fingers
during flexion (although not in ornithomimids and _Bambiraptor_,
apparently).  Unless you were a theropod that routinely hunted large
prey, then the forelimbs weren't of much use for grasping.  And even
then, the forward reach of the manus was limited - if
_Acrocanthosaurus_ (which presumably did hunt large prey) is anything
to go by (Senter and Robins, 2005).  First contact was probably made
with the jaws, with the theropod literally standing over the prey, and
the forelimbs were then used to secure or dispatch the prey.  It's no
surprise that many theropods might have turned their forelimbs toward
other purposes - such as crevice-probing (_Chirostenotes_,
_Epidendrosaurus_), procuring vegetation (ornithomimosaurs, maybe
therizinosaurs), digging (alvarezsaurs), aerial locomotion
(paravians), etc.  Or, they just shrunk the forelimbs altogether and
got them out of the way (e.g., carnotaurines [probably vestigial],
compsognathids, tyrannosaurids).