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RE: Extinction



This is a complicated question: geocard asks how today's(?)
frogs and toads can survive a change in temp. if a change in
temperature polished off the dinosaurs.  There is lots of work
going on right now in this field.  

First of all, todays amphibians and reptiles are a lot smaller
than dinoaurs and are able to dig in and insulate themselves
a lot easier than a huge animal such as a dinosaur could. 

Studies are underway that have found substances known as 
cryoprtectants that are mobilized in some species when exposed
to sub-zero temperatures, resulting in total freezing.  When
these species thaw out they are alive and well.  No amphibian
or reptile can survive very hot temperatures for very long, 
however (e.g. varies with species with upper limits about 100-105 
F for some). 

Thus selection favored smaller species and the largest reptiles
today (crocodilians which are relictual) and primitive snakes
such as boas and pythons are all tropical or neotropical species.
Ditto for largest lizards (monitors). The further north you go
the less likely you will encounter extremely large species
of amphibians or reptiles.   The Wood Frog (Rana sylvatica) 
has been found completely frozen inside blocks of ice within
the arctic circle. When thawed they are alive and fully 
functional.  I myself have witnessed completely frozen baby
water turtles thaw out months after being frozen with similar
results.

Steve Grenard
grenard@herpmed.com