Re: snake/spider venom

[MICHAEL HABIB <habib@jhmi.edu>]

Just a couple of quick notes that may be of help

*Snakes appeared quite late in the Mesozoic, and the major radiations of snakes 
occurred after the K/T.  Thus, there were very few snakes that overlapped in 
time with dinosaurs.  Additionally, even small dinosaurs would be far too large 
(birds obviously excluded) for all but a giant constrictor to consume.  Snakes 
were probably primarily small mammal/bird predators historically, just as they 
are today (with plenty of lizard and frog eating exceptions, of course).

*Venomous snakes appeared even later, and the ancestral food for the venomous 
groups was probably small mammals/birds/lizards as well.  It certainly was not 
non-avian dinosaurs, since the major venomous groups of snakes appeared well 
after the K/T (to the best of my knowledge).

*What is the criteria you're using for "too strong"?  It is tempting to think 
of snake venoms as overkill because they are capable of doing damage (or even 
causing death) in very large animals.  However, it takes significant time for 
the venom to deal such extreme damage to large species.  Snake venom is a 
feeding adaptation, and as such, it must work fast enough to disable a prey 
item in a very short period of time (otherwise the prey escapes a far distance 
before death or has enough stamina to fight effectively).  Killing a mouse in a 
minute or two requires rather severe toxins.  If something kills a mouse in 90 
seconds, it may take a few minutes to kill a rabbit, and a few hours to kill a 
human.  In medical terms, a toxin capable of killing a human in a few hours is 
quite powerful, but it's really just a side effect of being able to kill small 
animals extremely quickly.

Cheers,
--Mike Habib


----- Original Message -----
From: pheret <pheret@pheret.com>
Date: Thursday, September 30, 2004 5:23 pm
Subject: snake/spider venom

> i have a question about the evolution of toxins in snakes and 
> spiders.  it
> seems that most of them have a venom that is way too strong for 
> the prey
> they kill.
> 
> do u think that creatures that r no longer around had a different
> tolerance for the venom?  i know insects are much the same, but i am
> assuming that snakes probably preyed on dinosaurs, etc., before 
> mammals.i wonder if they were harder to kill?  anyway, just 
> wondering aloud.
> anybody studying this?  i have read about the venom canals that 
> appear in
> a certain dinosaur's teeth but i have no idea which one (it has been
> mentioned here before).
> 
> thanks for any info!
> 
> pheret
> 
> -- 
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