Dinosaur DNA

[rowe@lepomis.psych.upenn.edu (Mickey Rowe)]

Just to throw a little fat on the metabolic fires...  As others have
said, merely showing closest affinity between birds and dinosaurs
wouldn't do much to show that dinosaurs were endothermic.  We already
think that dinosaurs are more closely related to birds than any other
living animals, so gaining molecular evidence for that position would
not effect the endothermy debate at all (except perhaps in the minds
of a couple of holdouts like Martin and Chatterjee).  That said, there
is a way that molecular evidence could add some interesting
information to the endothermy debate.  It's a long shot, though.  Keep
in mind that even if Woodward et al did find a dinosaur DNA fragment,
it was tiny.  It contained less than 200 base pairs.  Some genes
(e.g. the gene which is defective in the most common forms of muscular
dystrophy) are over a million base pairs long. 

However, let's imagine that we were able to find a significant length
of DNA coding for an enzyme.  Enzymes are proteins which catalyze
chemical reactions.  How well they do so is a function of temperature,
but enzymes from poikilothermic animals tend to work reasonably well
over an extended temperature range whereas those of homeotherms tend
to work very well over a restricted range.  Given a DNA sequence
coding for an enzyme, we could make the enzyme exactly as coded, and
measure how well it works as a function of temperature (presuming, of
course, that it was similar enough to other known enzymes for us to
make an informed decision as to what reaction it was "supposed" to
catalyze in the dinosaur).  How sharply peaked the rate
vs. temperature curve was for our hypothetical enzyme would give us an
idea as to whether or not the animal possessing the enzyme maintained
a constant body temperature.

The above scenario doesn't seem all that much more realistic than
recreating the dinosaurs from amber entombed bugs, but we all gotta
dream... 

-- 
Mickey Rowe     (rowe@lepomis.psych.upenn.edu)

P.S. RB, I couldn't hold back!