Re: Dinosaur Were Endotherms (sic)

["Ralph Miller III" <gbabcock@best.com>]

Luis Rey <luisrey@ndirect.co.uk> wrote:
> I find the evidence inconclusive. Many dinosaurs had complex crests and
> nasal passages that could have had turbinate structures. Also the fossil
> preservation of many skulls won't allow us to see if there were
turbinates
> or not. Soft tissue is not preserved. On the other hand, do all birds and
> do all endotherms have turbinates? I have heard commentaries
contradicting
> this.

I know that I confused the RT issue by erroneously stating that someone had
written that kiwis had no respiratory turbinates.  I was wrong; they have
them, despite their small tube-shaped nasal passages, which shows (as
Gregory S. Paul has pointed out) that RT's can be present without the
nasals being especially capacious in the region of the RT's.  This is
telling, because it means that the kiwi skull would fail the
Ruben/Jones/Geist/Hillenius test for RT's, and hence, this known endotherm
would be judged an ectotherm.  (The RT team conceded that pelicans had no
RT's, but their semi-aquatic habits were taken to be the reason these birds
didn't dehydrate).

Furthermore, when the above-named team quantified the nasal passage
cross-sections of fossilized dinosaur crania to compare with the
cross-sections of the respiratory turbinate regions of extant endotherms
and ectotherms, they apparently performed their sections anterior to where
the RT would most likely be found in life, for the probable site of the RT
in a dinosaur skull is (correct me if I'm wrong) in the middle of an empty
cavity farther aft which gives no indication of the dimensions of nasal
passages.  As Luis Rey suggests, dinosaurs may have had RT's which simply
weren't ossified.  The illustration of the air flow through the nasal
passage of a dromaeosaur skull in the RT article in _The Complete Dinosaur_
has come under fire as inaccurate, based on an out-of-date restoration.

The RT team has noted the difficulty of finding evidence supporting RT's in
fossil birds, citing evidence for possible RT's in birds going back no
further than 70 million years ago, implying either that a good many
Mesozoic birds were something less than endothermic, or that testing for
RT's in fossil birds and (non-avian) dinosaurs is a difficult proposition
at best.       
 
> And I am of the opinion that is becoming clear that most (or all) small
> theropods were insulated with either protofeathers (like Sinosauropteryx)
> of feathers (like Protarchaeoteryx).
> It might be that the lack of feathers or other kinds of insulation in the
> fossil record of theropods is the true 'artifact of preservation'.

This is a distinct possibility, given the fact that there is no good
fossilized skin impression known for _any_ small dinosaur that supports a
non-insulated integument!  Correct me if I'm wrong.  Perhaps it is time for
Ruben, Jones, Geist, and Hillenius to submit a study of the metabolic
implications of extant ectothermic vertebrates which exhibit an insulating
coat of fibers (if they can find any).  

-- Ralph Miller III     gbabcock@best.com