Re: Rahonavis; sickle-claws

["Tim Williams" <tijawi@hotmail.com>]

Gerrit Hanenburg wrote:

> But seriemas have curved claws on pedal digit III and IV too.

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.  (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.)

> Anyway, this
> can be quantified with methods such as used by Feduccia (1993)

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.

(Of course, there is absolutely no reason to assume that the use of claws 
for climbing/perching and for predation are mutually exclusive.)



Tim

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