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Re: Re: Dinosaur theories.



>
>>Actually, the idea that dino metabolism varied among the group is the
>>majority opinion of dinosaur workers 
>
>Having just finished "The Dinosaur Heresies" I'd have to say Bakker's
>made a helluva case for high metabolism - far better than any I've seen
>for anything else, at this point.  Bakker's main strength, which I've
>seen from both "Heresies" and "The Hot-Blooded Dinosaurs" is that he
>seems to be a synthesist, and will freely drop a cherished theory in
>favor of one that fits more facts.

To my knowledge, Bakker has only ever dropped one cherished idea (dinosaur
polyphyly).  Indeed, he himself was instrumental in helping convince just
about everybody that dinosaurs had a single origin.

)That makes him rather an unusual
>scientist in general and nearly unique among paleotologists, as far as
>I can tell.

Alright, them's fightin' words!!!!  In any case, I admit that Bakker comes
off as a synthesist, and he certainly is a convincing writer.  However, the
data as they are actually found do not always fit his popular description of
them.  He likes to put things into a black-and-white perspective that really
isn't always there.

For example, Bakker does make a strong case that dinosaurs were more active
than modern reptiles.  This is something the majority of dinosaur workers
agree with.  However, he claims that the only means by which high activity
can be achieved is through mammalian-style endothermy.  There are other
mechanisms which have been proposed (such as gigantothermy) which would
allow a large dinosaur (but not small ones) to achieve "warm-bloodedness" on
an ectothermic engine.

Data which was not available to him when he wrote
"Heresies" show that dinosaurs had a mammalian growth style when juveniles,
then slowed down at adulthood.  This data includes growth rings in adult
dinosaur bones and the huge biomass in many dinosaurian ecosystems
(mammalian ecosystems do not appear to have this kind of biomass, probably
because of fuel requirements)

Other information which came to light after "Heresies" came out includes
Ruben's study of ectothermic vs endothermic muscle output, which suggests
that Archaeopteryx may not have had to have been warm-blooded to fly.

 >I found that t-rex mounted with his tail broken in three
>places to get him into the "right" position a testament to Bakker's
>attempts to cut through the bull and get the theory to fit the facts,
>not the other way around.
>

The tail-placement you're thinking of isn't Tyrannosaurus, and wasn't a
Bakker discovery.  The "broken-tail" incident concerns Iguanodon, and the
observations of Dave Norman (a rather conservative paleontologist with
regards to dinosaurian endothermy). I belive Bakker did discuss how
Tyrannosaurus held its tail, and the fact they made it too long, but this was
not a discovery of his, and was in fact known since the '40's.

>Perhaps you'd like to post some references for good rebuttals that might
>be available at my corner bookstore?  Or perhaps the rebuttals themselves?
>

Perhaps the best "rebuttal" (which is more a refining than an "attack")
would be Farlow's (and maybe a co-author?  I can't remember) chapter on
dinosaur physiology in Weishampel, Dodson, and Osmolska's _The Dinosauria_.
Also, Dave Norman briefly discusses in _The Dinosaurs!_ how the evidence for
endothermy in Deinonychus is very strong, but that for Brachiosaurus is
considerably weaker.

I'll add in conclusion that I greatly admire Bakker, and his paper in
Scientific American was very influential to my younger self, as was
"Heresies" when I was an undergraduate.  As a graduate student, though, I
found that his conclusions were not necassarily the most parsimonious ones,
and that appealing ideas might not necassarily be true.  I do think that
Bakker may be right about a great many things, but that he has not always
demonstrated those ideas to a great degree of certainty.
>Regards,
>Larry Smith
>larrys@alpha.zk3.dec.com
>
>

Thomas R. HOLTZ
Vertebrate Paleontologist, Dept. of Geology
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Phone:301-405-4084