Joined: Feb. 2006
It's a recent paper, out of Oregon State University.
Here is the link. I don't know if it is requires a subscription to view.
Here is the title and abstract:
Cardio-pulmonary anatomy in theropod dinosaurs: Implications from extant archosaurs
Devon E. Quick, John A. Ruben
Department of Zoology, Oregon State University, Corvallis, Oregon 97331
theropod heart • theropod lung • bird lung
Although crocodilian lung and cardiovascular organs are markedly less specialized than the avian heart and lung air-sac system, all living archosaurs possess four-chambered hearts and heterogeneously vascularized, faveolar lungs. In birds, normal lung function requires extensive, dorsally situated nonvascularized abdominal air-sacs ventilated by an expansive sternum and specially hinged costal ribs. The thin walled and voluminous abdominal air-sacs are supported laterally and caudally to prevent inward (paradoxical) collapse during generation of negative (inhalatory) pressure: the synsacrum, posteriorly directed, laterally open pubes and specialized femoral-thigh complex provide requisite support and largely prevent inhalatory collapse. In comparison, theropod dinosaurs probably lacked similarly enlarged abdominal air-sacs, and skeleto-muscular modifications consistent with their ventilation. In the absence of enlarged, functional abdominal air-sacs, theropods were unlikely to have possessed a specialized bird-like, air-sac lung. The likely absence of bird-like pulmonary function in theropods is inconsistent with suggestions of cardiovascular anatomy more sophisticated than that of modern crocodilians. J. Morphol. 2009. © 2009 Wiley-Liss, Inc.
Received: 8 September 2008; Revised: 16 February 2009; Accepted: 21 February 2009
And here is a Science Daily report about it.
I am not a paleontologist or bird expert, so I won't comment on the paper.