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Re: So-called sickle claws
In a message dated 97-10-02 13:01:31 EDT, email@example.com writes:
<< The claws of cats are held up by tendons (ligaments?) and the claws rotate
around the terminal toe bone, right? I mean, it's the claw that swivels,
not the toe bone- I think. Is that right? And cats have pads under their
toes for walking. Although you probably meant "an analogue" as to shape
and function only. >>
As I understand it, the claws of cats are homologous to our own fingernails,
and are thus made of the same kinds of proteins as hair; the claw sheaths of
raptors developed independently and are made of the same kinds of proteins as
feathers. Their origins are different--which leads to considerable anatomical
difference--but their overall shapes are convergently similar because of
their similar functions.
For example, cat claws could become retractable because, like fingernails,
they're anatomically disconnected from the distal unguals; but there's no
clear way for theropod or raptor talons to become retractable, because
they're wrapped around the distal unguals.
Overall, one would expect dromaeosaurid talons to be anatomically closer to
raptor talons than to cat claws--for example, in having a blood groove (which
is where this thread started, if I remember correctly).
(Corrections of any misconceptions in the above would be greatly