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Re: cold-blooded dinos (revisited)



At 10:09 AM 4/16/99 +0100, Chris Lavers wrote:

Concerning Ruben et al.'s interpretation of _Scipionyx_:

>Ruben's article about Skippy is very interesting. I think that most people
>now agree that Skippy had a ventilation system along the lines of
>crocodilians and mammals.

Well, actually, no.  Many paleontologists and other evolutionary biologists
remain extremely skeptical of the hypothesis of Ruben: the evidence for the
supposed hepatic piston remains weak and subject to alternate explanations.

Note, however, that this does not in and of itself mean that their final
conclusion (that non-avian dinosaurs may have had low resting metabolic
rates, but achieved high activity levels by greater ability to oxygenate
their blood than typical non-avian reptiles).

So, to address Barbara's initial question: the physiology of dinosaurs other
than birds still remains in question.  Many different models have been
suggested.  To name just a few: the Bakker version, where dinosaurs had
physiologies exactly comparable to modern therian mammals and to birds; the
Ruben version, where dinosaurs had cellular physiologies like typical
lizards and crocs, but some (by means of enhanced ventilation) had very high
activity levels; the Reid version (see, for example, Reid's chapter in _The
Complete Dinosaur_), arguing for high activity levels due to enhanced
ventilation, intermediate cellular physiologies as adults, and higher
cellular physiologies as juveniles; etc., etc.

>Ruben's ideas about Skippy are something of an about-face, and I am waiting
>for someone to criticise him for it.

Well, you could check out the dinosaur list archives, for starters... :-)

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661