> From: [EMAIL PROTECTED]
> Date: Mon, 19 Feb 2001 18:23:04 -0500
>
> It seems to me I read somewhere that gex have a fracture plane in one
> of the tail vertebrae that allows them to drop their tails. Am I
> remembering that correctly? Can they do it spontaneously or does it
> require some sort of physical stimulous, or does it vary by species?
Some (most?) species have several fracture planes. The plane is in
the centre of a vertebra, and the muscles and blood vessels adjacent
to it have modifications that minimize bleeding and close the raw end
to some extent. The regenerated tail has a rod of cartilege instead of
vertebrae, so it doesn't have fracture planes. The lizard can lose the
whole regenerated part, though.
While it's hard to say what is voluntary in a reptile, the tails can
drop without being grabbed by the predator. Perhaps it is triggered
by the hormones that are released by intense fear.
> Do you use the word autotomy with this?
Yes. Auto = self, tomos = cut.
Tail autotomy is almost certainly ancestral to all squamates (lizards
and snakes) because the tuatara (not a squamate) does it too. Some
squamates, like snakes and chameleons, have lost the ability.
There's a picture of a tokay and its freshly autotomized tail in one
of the AVS books, I think the one on tokays. You can see how the muscles
and skin have cleanly parted. I've also run into a reference to a paper
recommending autotomized gecko tails as a useful prep for studying the
nervous system.
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