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RE: Belly Ribs and air sacs

> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu]On Behalf Of
> Stephen V. Cole
> Ten years ago (the last time I bought a dinosaur book and went to
> Dinofest) Bakker was talking about finding belly ribs on a theropod
> (Trex?). Was this ever confirmed?

Actually, belly ribs had been known in theropods since the 1830s, and in 
Tyrannosaurus since the earliest 1900s.

> I'm an engineer, not a paleontologist, but as I understand it....
> Mammals and reptiles have elastic lungs. Air sucked in, air spewed
> out via the same plumbing. Two way street, less efficient.
> Birds have rigid lungs. Air is pulled into air sacks in the belly,
> then blow n out through different plumbing. I'm not sure if the air
> goes through the lungs on the inbound or outbound stroke, but the
> point is that air only goes one way through the lungs, which is more
> efficient and needed to fly.
> Belly ribs are needed to make air sacs work. If T-rex (or raptors or
> other theropods) had belly ribs, they had air sacs, and if they have
> air sacs, they are warm blooded. Belly ribs are mostly cartillage
> (except on Sauropods due to size) and dont fossilize well, so the
> idea that theopods used bird-type lungs is controversial and not
> accepted by eveyone until proven.
> In the ten years i was one, did anybody ever prove if theropods had air sacs?

Um, wow. Not to put too fine a point on it, but you have missed out on the 
decade of dinosaur respiration!

You can do searches in the DML archives for O'Connor, Claessens, Farmer, 
Carrier, and several others with regards to respiration.

However, the basic answer to your question can be found in:
Nature 436, 253-256 (14 July 2005) | doi: 10.1038/nature03716
Basic avian pulmonary design and flow-through ventilation in non-avian theropod 
Patrick M. O'Connor1 and Leon P. A. M. Claessens2

Birds are unique among living vertebrates in possessing pneumaticity of the 
postcranial skeleton, with invasion of bone by the
pulmonary air-sac system1, 2, 3, 4. The avian respiratory system includes 
high-compliance air sacs that ventilate a dorsally fixed,
non-expanding parabronchial lung2, 3, 5, 6. Caudally positioned abdominal and 
thoracic air sacs are critical components of the avian
aspiration pump, facilitating flow-through ventilation of the lung and 
near-constant airflow during both inspiration and expiration,
highlighting a design optimized for efficient gas exchange2, 5, 6, 7, 8. 
Postcranial skeletal pneumaticity has also been reported in
numerous extinct archosaurs including non-avian theropod dinosaurs and 
Archaeopteryx9, 10, 11, 12. However, the relationship between
osseous pneumaticity and the evolution of the avian respiratory apparatus has 
long remained ambiguous. Here we report, on the basis
of a comparative analysis of region-specific pneumaticity with extant birds, 
evidence for cervical and abdominal air-sac systems in
non-avian theropods, along with thoracic skeletal prerequisites of an 
avian-style aspiration pump. The early acquisition of this
system among theropods is demonstrated by examination of an exceptional new 
specimen of Majungatholus atopus, documenting these
features in a taxon only distantly related to birds. Taken together, these 
specializations imply the existence of the basic avian
pulmonary Bauplan in basal neotheropods, indicating that flow-through 
ventilation of the lung is not restricted to birds but is
probably a general theropod characteristic.

                Thomas R. Holtz, Jr.
        Senior Lecturer, Vertebrate Paleontology
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
        Mailing Address:
                Building 237, Room 1117
                College Park, MD  20742

Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796