warmblooded vs coldblooded dinosaurs

[Anusuya Chinsamy <anusuya@pobox.upenn.edu>]

Hi everyone

The question of dinosaur thermoregulation has been a point of much debate.
In recent years people have moved away from the idea of all dinosaurs being
endothermic - the latter being the view proposed by Bob Bakker and
supported by Greg Paul.  These days the idea of large dinosaurs being
gigantotherms is very popular - this  suggests that large dinosaurs
because of there sheer bulk are able to maintain a high body temperature.
 
My own research on dinosaur bone histology has shown quite  clearly that
dinosaur bone is neither exactly like mammals and birds which are
endotherms nor like that of reptiles which are endotherms.  In fact most
dinosaurs I have looked at have a bone structure that shows a kind of
mosaic pattern i.e. similarity with reptiles and mammals.  Furthermore in
a recent study published in Nature (17 March 1994) Luis Chiappe, Peter
Dodson and I show that three Cretaceous birds have growth rings in their
bone.  Such rings imply that bone is being formed cyclically (reptiles
typically do this).  This suggests that these birds are not
physiologically like their modern relatives and that they were not fully
endothermic.  These results further suggests that birds did not inherit
endothermy from a nonavian dinosaurian ancestor but they evolved it later in 
their
own evolutionary line.

I hope this short explanation helps.  Please also note that the terms
warmblooded and cold blooded are not really scientific.  It is better to
use the terms endothermic for the former and ectothermic for the latter.