Re: Vampire-osaurs?

[Phil Bigelow <bigelowp@juno.com>]

On highly-derived injection mechanisms (such as rattlesnake fangs), is a
living pulp cavity still present?

Evolving an internal venom channel from a primitive lateral fossa doesn't
seem too complicated, but then you have to re-plumb the output of the
venom sac (from draining into the mouth, to draining into the inside of
the tooth).

Hans D. Sues found reptilian teeth from the Triassic that have the
opening of the venom channel on the side of the tooth rather than on the
tip of the tooth.  It is a fully developed foramen, not a fossa.

<pb>
--


On Wed, 07 Jul 2004 11:04:37 -0400 Ronald Orenstein
<ron.orenstein@rogers.com> writes:
> At 01:00 AM 7/7/2004, Eric Hall wrote:
> >Are there any theories on how hollow teeth (or spines) and venom 
> sacs
> >evolved?  I myself can't come up with the vaguest notion how this 
> might have
> >happened, in any animal.
> 
> Harry Greene's book "Snakes: the Evolution of Mystery in Nature" 
> (University of California Press, 1997) contains a discussion of this 
> 
> subject of starting at page 91, under the heading "The evolution of 
> venom 
> injection mechanisms".  This is part of an extensive chapter on 
> venoms and 
> their delivery mechanisms, with very thorough descriptions of the 
> differing 
> types in snakes.  He points out that than the glands appear to have 
> derived 
> from Duvernoy's gland, a widespread feature of both venomous and 
> nonvenomous snakes.  These glands, and true venom glands, are 
> "derived 
> embryonically from tissues that produce tooth enamel...  As for 
> venom 
> conducting teeth, the formation of a groove, or closed canal, 
> obviously 
> facilitates the flow of secretions into a victim's tissues.  The 
> initial 
> evolutionary enlargement of rear teeth, however, could simply have 
> aided in 
> holding prey prior to the origin of specialized glands or even made 
> it 
> possible to puncture the puffed-up bodies of toads as well as 
> enhance the 
> inoculation of toxic secretions.  In any case, two large adjacent 
> teeth 
> also might have formed together a crude groove (e.g., as in some 
> litter 
> snakes), thus further exposing tissue to...  gland secretions."
> 
> 
> --
> Ronald I. Orenstein                           Phone: (905) 820-7886
> International Wildlife Coalition              Fax/Modem: (905) 
> 569-0116
> 1825 Shady Creek Court
> Mississauga, Ontario, Canada L5L 3W2          
> mailto:ron.orenstein@rogers.com
>          
> 
> 
> 
> 



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