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New paper on archosaur respiration
The first of several new papers on respiration in modern and extinct
archosaurs (including non-avian dinosaurs) by David Carrier and Colleen
Farmer is just out. The reference is:
Carrier, D.R. & C.G. Farmer. 2000. The integration of ventilation and
locomotion in archosaurs. American Zoologist 40:87-100.
This represents the print version of their presentation at the 1999 SICB
conference; for those who like to delve into the dinosaur list archives,
here is the article I posted concerning their (and others) talks:
This is their summary article: there will be a paper in Paleobiology looking
at the evolution of their proposed mechanism(s) throughout archosaur
evolution, and a pair of papers in the Journal of Experimental Biology which
document their work with living alligators.
Okay, to the details:
Carrier & Farmer have observed that the respiration of alligators is not
restricted while they walk (as in most lizard groups). Instead, alligators
combine costal (rib) and diaprhagmatic breathing, the latter incorporating
the unique mobile crocodilian pubis. Birds, meanwhile, raise and lower
their pelvis as part of a pump involved with breathing.
Carrier & Farmer suggest that the two different methods of pelvic aspiration
are modifications of the same ancetral system. Following earlier
suggestions by Lambe, Perry & (most recently) Claessens, they suggest a
method (which they call "cuirassal breathing") in which the gastralia of
archosaurs had at least a partial respiratory function. The suggest that
contraction of the M. ischiotrunchus (which runs from the ischium underneath
the bottom of the pubis to attach down the midline of the gastralia) would
increase the volume of the body cavity, and thus aid in inspiration.
In particular, cuirassal breathing might have been especially significant in
non-avian (or maybe non-ornithothoracine) theropods, which have a derived
gastralia pattern (the gastralia overlap in a zig-zag pattern of joints down
the middle, rather than forming simple chevron patterns). They also suggest
that the elongate pubes of theropods and the pubic boot of many theropods
would help to orient the force of the isotrunchus, giving a sufficient
moment arm to cause ventral rotation of the gastralia. In this way, the
gastralia would not merely bow backwards and outwards, but downwards too.
There's other stuff there; if you can find the article, it is worth the
Thomas R. Holtz, Jr.
Department of Geology Director, Earth, Life & Time Program
University of Maryland College Park Scholars
College Park, MD 20742
Phone: 301-405-4084 Email: firstname.lastname@example.org
Fax (Geol): 301-314-9661 Fax (CPS-ELT): 301-314-7843