Cardiopulmonary Function in Archosaurs During Hypoxic Exercise

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It is well known that birds can fly at altitudes where the partial pressure of oxygen is so low that mammals cannot function, but it is not known whether the sister group of birds, the crocodilians, have the physiological responses and pulmonary structures to support activity in hypoxic conditions. Conditions of low oxygen cause animals to breathe excessively, which then reduces the tension of carbon dioxide (CO2) in their blood. Low CO2 tension in turn reduces blood flow to the brain of mammals, leading to disorientation and even death. In contrast birds tolerate low blood CO2 levels without these adverse effects. Furthermore the pattern of air and blood flow in the lungs of birds, a crosscurrent design, facilitates the absorption oxygen by blood under conditions of low oxygen. Birds and crocodilians share a common ancestor dating back to the Mesozoic, a time of environmental hypoxia compared to today's atmosphere. Are the features that allow birds to function in environmental hypoxia a primitive archosaur trait or are they derived? If they were present ancestrally, then an exceptional ability to exercise under conditions of hypoxia may partially explain why archosaurs dominated the Mesozoic terrestrial fauna. To address these questions this project will study how air and blood move in the lungs of American alligators, as well as whether low CO2 tension affects brain blood flow. These studies will shed light on the evolutionary connections between the crocodilian and avian pulmonary systems. This research will test the hypothesis that crocodilians have a simple crosscurrent lung design and, if correct, then only a few small modifications would be requisite for evolution of the more complex avian lung. Thus, this research will potentially impact both the scientific community and the lay community, because it will provide insight into why and how archosaurs dominated the Mesozoic and it may provide a plausible explanation for the evolution of the avian lung. This project will also support the training of students, including those from groups underrepresented in the sciences.