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Re: dino-lice



Jason Brougham <jaseb@amnh.org> wrote:

> Senter (2006) found that the second finger in Dromaeosaurs was so flexible
> that Deinonychus could stab itself in the palm with its claw (Fig. 3 C).
> The first ungual could flex at 88 degrees to the phalanx! Gishlick (2001)
> found about the same thing.
>
> Thus, the literature shows extremely developed grasping ability in
> maniraptorans.


I'm not arguing that individual fingers were incapable of an
impressive amount of flexion; clearly they were.  However, what I am
saying is that as a unit, the manus was not very useful for grasping
small prey.  This inability is standard for theropods - and the
elongation of the fingers, combined with the altered range of motion
proscribed by the semilunate carpal joint, constrained the grasping
ability of the maniraptoran manus even further.  The manus had no
one-handed prehensile ability, and (with the exception of
_Bambiraptor_) could only capture prey in a two-handed fashion.


Gishlick and Senter both came to the conclusion that _Deinonychus_
could not grasp an object with one hand - unless that object was
pressed by the manus against its chest.  _Bambiraptor_ was
reconstructed by Senter as having an opposable manus - but he also
made it clear that this morphology was apparently unique among
theropods.  Typically in theropods, the fingers diverged too much
during flexion to have been capable of enclosing a small object.  So
in order to capture small terrestrial prey, _Deinonychus_ would have
had to scoop an object up with both hands.  In _Deinonychus_, as with
any other maniraptoran, feathered forelimbs would have made this
difficult.


_Deinonychus_ would have no difficulty grasping large prey, because
the forelimbs would have grasped the prey in a two-handed fashion.


> This feature is actually what the group was named after.


Maniraptorans were named after a raptorial manus; yes, I know.
Nevertheless, among non-avian maniraptorans, hypercarnivorous
predators such as _Deinonychus_ and _Velociraptor_ may have been the
exception in terms of carnivorous habits.  Many maniraptorans were
likely herbivores (or at least omnivores), including oviraptorosaurs,
therizinosaurs, scansoriopterygids, and basal troodontids - all of
which had a maniraptoran manus.  So the correlation between predatory
ability and the presence of a maniraptoran-style "raptorial" manus is
not especially tight.  Alvarezsaurs, as discussed at length on this
thread, departed radically from this forelimb morphology.


Check out Zanno & Makovicky (2010) for the recurrence of
herbivorous/omnivorous adaptations among theropods in general, and
maniraptoriforms in particular.




Cheers

Tim