[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. 

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

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. 

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! 

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. 

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.