An understanding of the origin of vertebrate respiratory systems- how very different lung structures and breathing mechanisms evolved- has been constrained by the rarity of soft-tissue preservation in the fossil record. The problem may be circumvented by taking an integrative approach that employs both observations on living animals and a survey of hard tissue structures preserved in extinct forms. The project will focus on the evolution of lung ventilation in the Archosauria, a group of animals that includes dinosaurs, crocodilians and birds. The two living archosaurian groups, birds and crocodilians, exhibit distinct and seemingly unique respiratory mechanisms. Bird lungs are interconnected with non-respiratory air sacs, and air 'circulates' unidirectionally through lungs of fixed size; crocodilians have two-way flow and an accessory muscle that moves the lungs. The skeletal movements of the respiratory cycle (inhalation and exhalation) in birds and crocodilians have not been studied in detail. This work will represent the first attempt to correlate the mechanics of respiration with a detailed analysis of bony features, especially those that are indicators of specific movements and those that constrain movement. This combined approach represents the most promising basis on which to trace the evolution of diverse respiratory systems that is represented with the Archosauria. Specifically, this investigation will: 1. Analyze the respiratory kinematics of the trunk skeleton of birds and crocodilians through cineradiography (x-ray recording of living animals); 2. Identify and trace osteological (bony) characters and their functional implications within the archosaurian fossil record; 3. Assess the functional and structural data in a phylogenetic context (that is, in terms of evolutionary relationships inferred from other evidence) to understand evolutionary patterns.
