Cardio-pulmonary anatomy in theropod dinosaurs: Implications from extant archosaurs.
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.
Quick
Devon E
DE
Department of Zoology, Oregon State University, Corvallis, 97331, USA. quickd@science.oregonstate.edu
Ruben
John A
JA
D000400:Air Sacs / Q000033:anatomy & histology; D000489:Alligators and Crocodiles / Q000033:anatomy & histology; D000818:Animals; D001717:Birds / Q000033:anatomy & histology; D001842:Bone and Bones / Q000033:anatomy & histology; D025061:Dinosaurs / Q000033:anatomy & histology*; D006321:Heart / Q000033:anatomy & histology*; D008168:Lung / Q000033:anatomy & histology*; D010388:Pelvis / Q000033:anatomy & histology