Re: Dinosaurs Were Endotherms (long)

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

Speaking of kiwis and their nasal passages,
Matthew Troutman <m_troutman@hotmail.com> wrote:
>     Yes, that may well be true, but the posterior cavity is still 
> bigger (than the anterior nasal passage in the kiwi -- RM). 

Just so.  Which is why I wrote:
 
GSP went on to say that the kiwi's posterior nasal 
> passage
> >contains more complex conchae and is larger in cross-section; however 
> it is
> >_short_ and it is _narrower_ than the same region in other birds, -SNIP-

Matthew Troutman: 
>      I am not sure about this, because some of the kiwis I have seen, 
> though they do have small posterior cavities, it is still rather large.

?
 
> One must remember that that hypothetical theropod nasal passage is 
> hypothetical -SNIP-

That's why I used the term "hypothetical."

> Kiwis are also 
> somewhat specialized in their nasal cavities because the external nares 
> are shifted rostrally and the anterior facial region is elongated. In 
> theropods the external nares are still not completely rostral and their 
> anterior facial region is not laterally and dorsal-ventrally compressed 
> and condensed. 

The papers by Ruben et al. base their argument on internal anatomy, and I
was responding in kind. 

> The
> >nasal passage proper cross-section can be approximated, but aft of 
> that,
> >there lies only a vacant cavity, which may or may not have housed the
> >elusive middle respiratory turbinate.  The interesting thing about this
> >chart is that the kiwi would probably not make the grade as an 
> endotherm by
> >this standard, although this point is not made in the articles.
 
>      The posterior region probably would have, since it still is rather 
> large compared to that of the dinosaurs studied.

Again, the chart I mentioned does not refer to the posterior nasal passage,
and hence, the kiwi would probably flunk this test of the anterior "nasal
passage proper."
 
> Still, there does not 
> seem enough room for there to be a posterior region in dinosaurs.

We disagree.

 Look 
> closely at the Ornithomimus skull in _ The Complete Dinosaur _, the 
> whole entire pre-antorbital cavity region in Ornithomimus is narrow,

...as is the anterior nasal passage of the kiwi...

> and 
> based on the figures in the Science paper, the Ornithomimus skull is the 
> least likely to have been distorted since the skull is still 
> symmetrical, even from that of the CT scans. Based on the pictures in 
> Bakker's Discover paper, you can see from a dorsal perspective that the 
> snout is continuously narrow, even from the spot where you propose the 
> middle turbinate is!

Yes, the snout could be described as "narrow," but I still see a vacant
space which could have housed the middle respiratory turbinate. 

> >In _Science_, Volume 270, 11-3-95, page 735, it is stated that John R.
> >Horner thinks that dinosaurs may have had respiratory turbinates, 
> claiming
> >that he had found a turbinate attachment ridge on the CT scan of a
> >hadrosaur skull.  "It meets all the criteria by which Ruben 
> distinguishes
> >respiratory turbinates from olfactory ones, he (John R. Horner) says."
 
>      I don't know much about this issue and I think I heard somewhere, 
> possibly in the Ruben et al. 1996 paper, that Horner has retracted his 
> views.

A more precise reference for Horner's retraction would have been
appreciated.

In my opinion, the respiratory turbinate papers make a strong argument
against endothermy in non-avian dinosaurs until you take a closer look at
the actual data (versus the interpretation and presentation of the data),
and at this point you must decide for yourself whether the authors have
truly taken an even-handed approach to the subject and whether theirs is
such an open-and-shut case.

Ruben et al. have presented a number of papers which present an ongoing
critique of the modern view of dinosaurs as active, social creatures which
have much in common with birds.  I have not seen studies replicating their
research and reaching the same conclusions, but I have seen Philip J.
Currie persuasively refute their hypothesis about the _Sinosauropteryx
prima_ fibers.  Advocates of ectothermy in all non-avian dinosaurs will not
succeed in convincing me until they can explain the metabolic mandate for
an insulating pelage on small ectothermic theropods.

-- Ralph Miller III     gbabcock@best.com