Sickle-claws and retraction (was Re: New Velociraptorine)

["Tim Williams" <T.Williams@cclru.randwick.unsw.edu.au>]

Sam Girouard wrote
 
>         Really? Ever since Bakker's restoration of Deinonychus back
> in the 60's it has been unanimously assumed that all "sicle-clawed"
> theropods [....]  held their "killing claws" clear above
> ground. However, I object to this mode of restoration for several
> resons.
>
> I have even read an account of a rhea killing an Australian boy by
> slashing his throat with one such claw.

One of these two was a long way from home.  Rheas are South American 
birds.  The perpetrator may have been a cassowary, a ratite from 
Australia and New Guinea renowned for its filthy temper.

> Third, the wear experienced by normal locomotion would have been
> miniscule compared to repeated contact with bone while dispatching
> prey (if the claw were even used in this role at all).

Not if the sickle-clawed theropod struck at the soft underbelly.  A 
nice, swift evisceration, and down goes the prey.

[ Are we being a bit too mammalocentric here?  Would an animal with a
  rib cage extending all the way to its pelvis have a "soft underbelly"?
  -- MR ]

>         Fourth, I do not know of any articulated theropod feet that show any
> evidence of a retracted claw. This probably doesn't provide a good
> indicator, after all the animals had died and dried, but negative evidence
> beats no evidence at all.

Like the lack of didactyl footprints, absence of evidence is not
evidence of absence.

Tim Williams