[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: CNN on Lungs and Feathers
>Readers of the list beware. White is posting dubious information.
Every once in a blue moon you run into a comment that says more than any
deliberate parody -- one of those happy concurrences of passion and
language which artifice could never improve. I'll leave this one alone.
Next, I reserve the right to be wrong. I frequently am. Just ask my
>He suggests that birds can ventilate air-sacs only via "perching", or via
>flight induced depression of the sternal plate. This is, of course, absurd in
>that many birds neither fly nor perch. It is also nonsensical, because kiwi
>and elephant bird sterna are far too short to ventilate the majority of their
>air-sacs (and are smaller than those of dromaeosaurs). Only the posterior
>ribs can ventilate the large posterior air-sacs in these flightless,
>nonperching birds! The muscle action birds use to operate the posterior ribs
>have been described. Of course, I've pointed this out multiple times on this
My understanding is that non-flying, non-perching respiration in birds is
ultimately the same as flying respiration and so is subsumed under the
same general rubric. Somehow, the dorsal ribs must be pulled forward,
which in turn pulls the ventral ribs forward, which ultimately expands
the posterior air sacs in ratites as in other birds. Rib compression, as
I understood you to espouse, is not part of either of these respiratory
Avian style respiration also tends to be associated with a number of
skeletal specializations which are mentioned in your very useful post of
4/19/97. Many of the key adaptations to avian respiration do not appear
to exist in Sinosauropteryx, e.g. shortening of the first dorsal ribs,
elongation of the posterior ribs, absent lumbar region (?), elongated
sternal complex, and retroverted pubes.
>That some modern reptiles have air-sacs is irrelevant because, unlike
>theropods, they do not have a means of ventilating them. Sauropods did have
>the specialized, mobile posterior ribs needed to operate their sacs.
The assertion that was made was that the inferred presence of air sacs
was strong evidence for an avian or pre-avian mode of respiration.
Clearly, the presence air sacs is not a particularly strong indicator of
avian respiration. Also, once again, I don't see any evidence for this
adaptation in Sinosauropteryx. To be fair, my comment was actually on
another point -- namely that posterior air sacs sem to be rare in
Theropods as a general matter, and they become rarer as one moves back to
the Late Jurassic and the time of Archaeopteryx.
My understanding was also that the air sacs of reptiles are in fact
ventilated. Am I wrong on this?
Incidently, are you arguing that Apatosaurus had a bird-like respiratory
system? I hadn't heard this claim before.
>White also says that the pubes of theropods are less retroverted than in
>Archaeopteryx. This reflects a basic lack of familiarity with the data both
>in the literature and on this list. All the 20th century specimens of the
>urvogel show that the pubis was nearly vertical, including the newest
>specimen in which the pubo-ilial contact is clearly preserved intact (and was
>carefully described and illustrated by Wellnhofer). In articulated
>dromaeosaurs the pubes are severely retroverted, much more so than in
>Archaeopteryx. In the alvarezsaur Parvicursor the pubes are so retroverted
>that they actually articulate with the ischia along their entire length!
Apparantly a woeful ignorance of Archaeopteryx shared by many, including
one of the Encyclopedia authors. I did go back and check my sources:
the Encyclopedia, Ruben et al. (relying on Martin) and one of your(?)
illustrations from, as you say, a few years ago. I also looked at a
picture of one specimen (sorry, I couldn't tell which) which looked like
road-kill and could have been either way. Dunno what to think in view of
your assertion, but its a bit tangential to Sinosauropteryx.
>White's assertion that pterosaurs were not endotherms is without basis. As
>Unwin has shown, they were insulated, which is virtual proof that the
>majority of body heat was generated internally (endothermy). No ectotherm can
>insulate itself against the external heat sources it depends upon. The highly
>pneumatic pterosaurs almost certainly had a well developed air-sac complex,
>with the means to ventilate it (a sternum larger than seen in some birds, and
>a mobile pre-pubis), so respiratory capacity should have been very high. Of
>course, the very large flight muscles indicated by the large sternum,
>enormous pectoral crest and big arms required an aerobic capacity as high as
>in flying birds and bats.
Umm. Debated, perhaps. "Without basis," no. Endothermy in Pterosaurs
remains something less than a concensus view. In any case, the point
was that air sacs are common just about as far back as you care to go.
Again, we can't assume avian respiration because of the inferred
existence of air sacs. Flight, endothermy, and air sacs are not a
>Contra White, the theropod hepatic pump hypothesis does not present a very
>important evolutionary puzzle, because it is entirely spurious and will soon
>be falsified. There is literally not a single item of soft tissue or
>osteological data that contradicts the long standing, well founded, majority
>opinion that tridactyl theropods evolved a preavian air-sac complex. White's
>idle comment on the examination of the Sinosauropteryx specimen is valueless
>because he has not seen it, unlike Currie, a highly qualified paleontologist
>and biologist who has carefully examined the feathery beast multiple times
>with various optics.
I'm having trouble remembering which idle, valueless comment this was.
You mean that it seemed subjective? It was your idea that Ruben's group
had seen only what they wanted to see and that it was hard to tell
anything from roadkill without personal inspection. I think that's a
valid criticism. Hopefully, Currie can clear this up. But it would be
better if the OSU group also undertook the personal inspection for
precisely the reason you suggest. What is likely to happen now is that
this will merely set up a series of treks to the mysterious East, each
pilgrim returning with tales of new wonders, and none in agreement.
Paleontology should, perhaps, be conducted more sytematically than
Medieval geography. If they went together, y'see, they'd not only save
money (and have much more interesting dinners), but we might get
agreement on at least what the disagreements were rather than a lot of