Re: Dinosaurs Were Endotherms (long)

["Matthew Troutman" <m_troutman@hotmail.com>]

>>      I believe GSP was just refering to the anterior nasal passage in 
>> the kiwi.
>
>Yes and no.  Gregory S. Paul does state, of course, that the anterior 
nasal
>passages of the kiwi (and some seabirds) is very narrow, and well below 
the
>reptilian line in this dimension, but that these anterior nasal 
passages
>none-the-less contain turbinates.  

    Yes, that may well be true, but the posterior cavity is still 
bigger.

You're right about this, and this was
>his main point.  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,
>consistent with the relative dimensions of the hypothetical theropod
>passage at this location (though the dimensions and configuration of 
the
>actual air passage in the midst of the theropod antorbital fenestra can
>neither be proven nor falsified on the basis of available fossil 
material).

     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 and fossils are needed to support this. 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. 

> This posterior nasal passage is the site of the middle respiratory
>turbinate in modern birds (see the _Science_ paper for an illustration 
of
>this location in birds).  So my previous statement that kiwis had
>exceptionally narrow posterior nasal passages was wrong, for which I am
>sorry, but my conclusion remains the same, as I shall explain.  

     Based on this, then Nanotyrannus could not have had turbinates. 

 In Paul's post on 1-29-98, he states that the complete
>_Velociraptor_ skulls now available reveal a long and fairly complex 
nasal
>passage in dromaeosaurs.

     How long it is does not matter. Neither does complexity since the 
crocodilian nasal passage has features that you might consider 
"complex".

>Paul states, furthermore, that the anterior nasal passages of
>_Nanotyrannus_ are crushed, casting doubt on the usefulness of the
>specimen.  As for the _Ornithomimus_ CAT scan depicted in _The Complete
>Dinosaur_, the specimen appears to me to exhibit a posterior cavity 
which
>(based on its size) could, indeed, have housed a cartilaginous middle
>respiratory turbinate.  Would anyone care to comment on this figure?

    The crushing in the anterior portion of Nanotyrannus is discuused 
briefly in the Science paper. Underneath Fig. 2 :  " Some minimal 
postdepositional distortion of these fossils is evident. Nevertheless, 
the relatively narrow nasal passages in the dinosaurs indicate that, as 
suggested by their fossils, respiratory turbinates were probably absent 
in the living animals". Regardless of whether there is some crushing; 
look at the pictures! To make the nasal cavity bigger, there would have 
to have to been an extremely wide anterior facial region. Plus they 
state that the CT-scans were taken from mid-snout region, which would 
indicate that the whole passage was narrow. 
     


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. Still, there does not 
seem enough room for there to be a posterior region in dinosaurs. Look 
closely at the Ornithomimus skull in _ The Complete Dinosaur _, the 
whole entire pre-antorbital cavity region in Ornithomimus is narrow, 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!

>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.




>See above.  The figures of _Nanotyrannus_ and _Dromaeosaurus are of 
dubious
>value, and the antorbital fenestra cavity directly adjacent to the
>illustrated air flow path on view in the oblique _Ornithomimus_ cat 
scan on
>page 514 of _The Complete Dinosaur_ looks to me like a viable location 
for
>middle respiratory turbinates.  It is in the right spot, and would 
appear
>to provide plenty of room!

     The diameter of the nasal passage appears fairly continuous in 
Ornithomimus and even if there was an expansion, it would not be much. 
  
MattTroutman

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