Re: Dinosaur theories.

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

>    Hi everybody,
>    
>    I am by no means a dinosaur expert, but I've been interested in them
>    since I was a little kid.  This list has been highly informative and
>    entertaining, so first I'd like to thank everyone who's been
>    contributing to it.
>
>    There is something that has been puzzling my amateur mind for quite
>    some time.  There seem to be two big theories in the dinosaur world,
>    the first being that dinosaurs were cold-blooded and closely related to
>    reptiles, and the second being that they were warm-blooded and closely
>    related to birds.  Are there any scientists arguing on behalf of both
>    theories?  That is, that some dinos were cold blooded and some were
>    warm blooded?  Has anyone tried to argue that some dinosaurs could be
>    related to mammals?  Triceratops always looked suspiciously like a
>    rhino to me, but I'm sure there are enough skeletal differences to blow
>    that silly theory out of the water.
>
>    Thanks for the info.

Actually, the idea that dino metabolism varied among the group is the
majority opinion of dinosaur workers (although not the belief of Bakker and
Paul, who are two of the more well-know scientists in the public eye).
There is growing evidence that dinosaurs may have been warm-blooded as
juveniles, then shifting to a medium-metabolism at adulthood.  There are
problems with wholly-endothermic brachiosaurs, for example, that would not
be encountered by small coelurosaurs.  As has been stated since the '70's,
the best evidence for endothermy is found in small theropods.

As towards classification, modern systematics puts dinosaurs within Reptilia
(Sauropsida to some), which is a more inclusive group than traditionally
used, as it contains the birds.  As you know, there is an active debate as
to the origin of birds, but either of the leading ideas (birds arose within
dinosauria, or birds arose within Crocodylomorpha) puts birds as a subgroup
of reptiles.  Also, under this system, the "mammal-like" reptiles are not
reptiles, but are instead the more primitive members of the Synapsida, the
sister group to Reptilia.

>
>    Todd Hensley,  hensley@nwoca.oecn.ohio.gov
>    ------------------------------------------------------------------------
>    There's things that will knock you down you don't even seen coming,
>    and send you crawling like a baby back home.
>
>
>

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