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Re: New Deinocheirus specimens found, indicating basal ornithomimosaur

Thomas R. Holtz, Jr. <tholtz@umd.edu> wrote:

> The manual claws of Deinocherius are most definitely NOT raptorial! However, 
> I understand when just viewing them from a distance
> they might appear so. Handling the actual specimens (or casts), you find they 
> are much thicker, much less pointed, and so forth than
> people commonly think: more like the claws of basal therizinosauroids.

I think the reason why the claws of _Deinocheirus_ are so often
referred to as "raptorial" (such as the chapter on Ornithomimosauria
in Dinosauria II) is to contrast the claws of _Deinocheirus_ with
those of other ornithomimosaurs.  _Deinocheirus_' unguals are much
more curved than is typical for ornithomimosaurs (even _Gallimimus_
and basal forms), with relatively large flexor tubercles that are
proximally positioned.  Ornithomimosaur unguals are distinctly
non-raptorial (especially in the flat-clawed taxa), with weak and
distally positioned flexor tubercles.  True, the unguals of
_Deinocheirus_ are fairly blunt and poorly recurved  - a long way from
the highly tapered and recurved unguals with an ovoid cross-section
seen in undoubted theropod predators.  But among ornithomimosaurs, the
claws of _Deinocheirus_ stand out - and not just for their size.

The overall forelimb of _Deinocheirus_ was also more mobile compared
to other ornithomimosaurs: the humerus could probably be raised much
higher above the horizontal (no 'supraglenoid buttress') and the
forerarm was capable of pronation/supination (radius/ulna not
appressed).  So the forelimbs were most likely used for more than just
the hooking/clamping function inferred for ornithomimosaurs like
_Struthiomimus_.  The hands of _Deinocheirus_ seem more adapted for
grasping, even if they weren't predatory/raptorial.

The hands of _Deinocheirus_ might have been adequate to grasp small
prey (presumably two-handedly), if it was an omnivore.  Or the long,
curved and fairly blunt claws could have been used to slash or swipe
attackers, since the aim was not to impale or seize prey, just wound
an attacker.  The smaller and highly cursorial ornithomimosaurs had
the option of running away from a predator - but _Deinocheirus_, being
more ponderous and far less cursorial, likely needed another strategy
to ward off an attacker.  That's one hypothesis, anyway.