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Re: Balaur bondac, the double-bladed dromaeosaurid of Transylvania!
T. Michael Keesey <email@example.com> wrote:
> It has the usual number of digits; it's just that digit I
> is hypertrophied like digit II. (Homeotic shift?)
> The hands, OTOH, are didactyl (with a slivery remnant of
> digit III)!
Yes, the hand is effectively didactyl, with digit III rendered nonfunctional.
The carpometacarpus is fused.
Thus, the hand of _Balaur_ is said to be "fused, atrophied, and poorly suited
for grasping." However, this has to be viewed in the context of the 'baseline'
maniraptoran manus. Maniraptorans typically have hands that are
non-prehensile. Thus, all maniraptorans would have had difficulty grasping
only with one hand. (The only possible exception is _Bambiraptor_, which seems
to have a manus that was autapomorphically modified for one-handed prehension.)
Thus, maniraptorans could only grasp objects in a two-handed fashion.
_Balaur_ seems to have taken this one step further, in the effective loss of
the third finger, and in having a fused carpometacarpus. (Carpometacarpal
fusion is also exhibited by the oviraptorosaur _Heyuannia_, as well as possibly
_Avimimus_ [the latter is noted in the paper].) So the highly derived manus of
_Balaur_ was likely capable of two-handed grasping. This has been previously
inferred for _Velociraptor_, which accords with _Velociraptor_'s preference for
large prey (such as _Protoceratops_). The manus unguals of _Balour_ certainly
look formidable, so the manus was apparently used for some defensive (or
offensive) function. This ties in with the double-bladed pes.