Re: Re: Re: Re: Dinosaur theories.

[Thomas_R_HOLTZ@umail.umd.edu (th81)]

>>In fact, it doesn't per se.  The body of evidence out there now (including
>>the work of Dr. Chinsamy and her colleagues) strongly suggests ontogenetic
>>heterometabolism; that is to say, radically different metabolic  rates and
>>functions between juveniles and adults.  For example, a hadrosaur or
>>sauropod hatchling may have started out as a mammalian-style endotherm, then
>>shifted gears, as it were, become a gigantotherm after reaching a certain
>>size.  This is different from most large endotherms today, in which the
>>metabolic rates slow down at adulthood, but the metabolic "engine" remains
>>the same.  Interesting, work on modern elephants suggests that they may not
>>be true endotherms, but gigantotherms of a sort.
>
>I am curious. Where did you get the above idea? I am in contact with these
>people frequently, and heard Dr. Chinsamy's talks many times and NEVER did
>I come away with the above statement!

Which of the above ideas?  The one from Chinsamy is the fact that metabolism
slows down tremendously at "adulthood" (before or after sexual maturity is
uncedrtain).  In any case, her work and others have shown that dinosaurs
(including many Mesozoic birds) had a "avian" style woven bone during
juvenile stages, indicative of fast growing rates typical of modern
endotherms.  However, growth rings as found in adult dinosaurs are absent in
all modern endotherms, but present in ectotherms.  This suggests firstly a
major shift in growth rates, and thus metabolism.  Additionally, it shows
that dinosaurs had a combination of growth regimes not found in any modern
animal group - very fast, woven bone growth as juveniles, relatively slow,
ringed growth when older.

>
>Mike Balsai
>
>
>
>

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