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Re: Rahonavis; sickle-claws



> When it comes to the "sickle-claw", it's not just size but what you do
with
> it that counts.  The large size of _Deinonychus_'s second pedal ungual,
> combined with its ability to execute a wide arc of movement, suggest that
it
> was wielded as a "slashing claw".  As such, the enlarged sickle-claw was a
> specialized instrument designed for predation.

As such, it exists only in "dromaeosaurs", troodontids and *Rahonavis*,
right?

> (Although *maybe* the
> hyperextensible sickle-claw was initially evolved as a climbing device, or
> was co-opted for such a purpose later on... but that's another story.)

Unlikely IMHO. The function of such a parasagittal climbing device could be
fulfilled much better by a pamprodactyl foot (all 4 toes point forwards),
which exists in mouse birds = Coliiformes, while a single enlarged claw on
II, III or IV which functions as a climbing aid does not exist in any bird
AFAIK.

> Feduccia's quantitation study of bird claws has one major weakness: it did
> not determine whether the arc of curvature associated with perching
ability
> was different to the dimensions for predation.  This blows a big hole in
the
> study - big enough for a tyrannosaur to walk through.

Quite literally because Feduccia also threw finger claws in and proclaimed
that Archie was arboreal mainly because of its strongly curved finger claws.
Those of *Tyrannosaurus rex* and many others have quite similar curvatures
AFAIK. By exaggerating his argument that way he muddied it -- the toe claws
of *Archaeopteryx*, although straighter than the finger claws, are still
more strongly curved than those of AFAIK many, if not even all dinosaurs
excluding perching and raptorial birds and sickle claws. Or is this false
memory? :-)