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RE: Extinction

A fruitful area to explore would be those vertebrates with ESD 
(environmental sex determination) where nest temperature would affect the 
male or female sex of the developing embryos.  If the dinosaurs had ESD and 
many of the other herps did not, then they may have died off because of all 
one sex populatioins.  Today, many turtle groups do have ESD but the 
cladistic pattern suggests that GSD (chromosomal or genetic sex 
determination) was the ancestral character and that may explain how turtles 
survived.  Their physiology is also much less sensitive to environmental 
variations.   Today, ALL crocodylians have ESD and being the living 
sister-group of dinosaurs this suggests that, one,  dinosaurs may have had 
ESD but two this does NOT explain how they survived the KT boundary. 
 Perhaps aquatic living or restriction to the tropics is a causative factor. 
 Unfortunately these hypotheses are bloody difficult to test with 
paleontological data.

Scott Moody, Ohio University
>From: dinosaur
To: Multiple recipients of list
Subject: Extinction
Date: Tuesday, April 25, 1995 8:13PM


  I am a new subscriber to this mailing list.  I am amateur dinosaur
enthusiast and I have heard several theories as to what
caused the extinction of the dinosaurs.  If the dinosaurs were killed off by
the impact theory, how could such animals like frogs and turtles survive a
big change in temperature?  I would apprectiate any information on the
subject.  Thank you.