Re: Belly Ribs and Breathing

["David Marjanovic" <david.marjanovic@gmx.at>]

----- Original Message -----
From: "Waylon Rowley" <whte_rbt_obj@yahoo.com>
To: <dinosaur@usc.edu>
Sent: Monday, July 02, 2001 12:17 AM
Subject: Re: Belly Ribs and Breathing


> [...]
> Ok, time for rampant hypothesizing. What if gastralia
> are not preserved in (most) ornithischia because they
> lack an avian respiratory system driven by the
> contraction/expansion of the air sacs?

Or if, as Bakker has suggested (The Dinosaur Heresies), their air sacs were
operated by a sort of diaphragm anchored on the prepubic process?

> So, in
> non-avian theropods the abdominal air sacs are sprung
> open using the outward tension stored in the gastralia
> after exhalation. In birds, the need for this is
> reduced, because they have ucinate processes on the
> ribs that make the contraction/expansion of the
> ribcage more uniform. Perhaps the need for more rapid
> breathing forced birds to adapt this new respiratory
> regime? What do you think?

Uncinate processes are much more widespread (Willo the *Thescelosaurus* has
huge uncinate plates). Well, here's what other people thought 3 years ago:

Leon P. A. M.[*] Claessens, Steven F. Perry, Philip J. Currie: Using
comparative anatomy to reconstruct theropod respiration, SVP meeting
abstracts 1998, p. 34A

(*Four first names? ~:-| )

"[...] Kinetic gastralia, jointed in a characteristic interlocking pattern,
may have been capable of further enhancing aspiration breathing.
        Unique functional anatomical correlates of the avian and the
reptilian lung system make it possible to determine the probability of an
avian or reptilian-like respiratory system in theropods based on skeletal
analysis.
        Saurischian dinosaurs, like birds, possess pneumatic bones in the
axial skeleton, indicating that the lungs were attached dorsally. Comparison
with recent reptiles indicates that attached lungs are heterogeneously
partitioned, and in advanced theropods the development of high-compliance
pulmonary diverticula may have approached that of cursorial paleognath
birds. Given the large size of many saurischians, the lungs were undoubtedly
multichambered.
        A combination of costal and gastralial movement would have sufficed
to support a constant, high aerobic level. The occurrence of a hepatic
piston pump is ruled out on osteological evidence. Although it is possible
that unidirectional air flow in the dorsal part of the lung became
established late in the theropod-avian transition [sic], the anatomical
prerequisitesfor avian degree cross-current gas exchange are already present
in the crocodilian lung, and thus may predate the origin of dinosaurs."

The last sentence fits well the finding that pneumaticity was widespread
among Archosauromorpha
(http://www.cmnh.org/fun/dinosaur-archive/2001Jun/msg00084.html, where I
didn't mention that prolacertiforms, and therefore in any case pterosaurs,
are inside (Rhynchosauria + Archosauriformes).

Enough abstract-retyping for today... :-)