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Re: Dinosaurs Were Endotherms (long)
Matthew Troutman <email@example.com> wrote:
> 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. 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).
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.
> He (referring to Gregory S. Paul) stated that Ruben et al. did measure
this (referring to the anterior nasal passages) in their papers
> on turbinates but did not measure the posterior nasal cavity, which can
> hold turbinates. This is incorrect because in the figures in the Ruben
> et al. Science paper and the Complete Dinosaur show the entire nasal
> passage highlighted.
A figure of _Dromaeosaurus_ and CAT scans of _Ornithomimus_ and
_Nanotyrannus_ do appear in the articles.
In the case of _Dromaeosaurus_, we see Philip J. Currie's complete skull
restoration (1995 JVP 15:578). Quoting Paul: "Of the snout, only fragments
of the premax, maxilla, vomers and palatines are known!" Had the authors
been concerned with accuracy, they should have illustrated only the
fragments of actual fossil skull recovered without relying on hypothetical
anatomical features. 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.
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?
As for the CAT scan cross-sections of extant animals and dinosaurs, the
comparison hardly seems proper, as it apparently shows only how the most
voluminous nasal passage region of the bird and the mammal (that area which
houses the middle respiratory turbinates) compares with the narrowest nasal
passage region (the nasal passage proper) of the dinosaurs. How
differently would these images appear were we to reverse the scheme? I
think we might have to conclude that mammals and birds are ectotherms and
that non-avian dinosaurs were endotherms!
I can view the chart of nasal passage proper cross-section vs. body mass
somewhat more charitably, but again, we are here looking not at the most
sizable cavities within the dinosaur crania, but only within the nasal
passage proper, because this is the only nasal cross-section that could be
measured in dinosaurs. Unfortunately, the value of this information is
questionable, in my view, because it doesn't refer to the most likely
location for middle respiratory turbinates in dinosaurs (basing the
expected site on the anatomy of their living descendants, the birds). 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.
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." It
is interesting that John R. Horner is listed as one of the authors of the
_Science_ article, _The Metabolic Status of Some Late Cretaceous Dinosaurs_
(_Science_, Vol. 273, 8-30-96)! Has there been any more written on the
hadrosaur turbinate ridges?
If there was a posterior nasal cavity, it would be
> very short because the internal nares are almost always opposite the
> antorbital cavity in dinosaurs. This would preclude RTs.
As in the short posterior nasal cavity of the kiwi (which contains RT's)?
> >>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
> weren't ossified.
Matthew Troutman responded:
> The position is verible, but the whole passage was narrow according
> to the figures in the papers. See above.
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 dromaeosaur skull in _ The Complete Dinosaur _ was one figured by
> Currie in 1995, hardly old. It may well be inaccurate, though.
See above. It is not useful to the discussion.
> Boy, I can feel the flaming getting closer.
Not from me. I have had to correct myself here, and may have to yet again.
I have not, personally, seen any direct evidence for respiratory
turbinates in non-avian dinosaurs, but I have seen no solid evidence
against them, either. So I don't think that we can draw any firm
conclusions on this matter until more fossil evidence is made public.
Anyone else out there with dinosaurs in the basement?
-- Ralph Miller III firstname.lastname@example.org