title: Unidirectional airflow in the lungs of alligators.
abstract: The lungs of birds move air in only one direction during both inspiration and expiration through most of the tubular gas-exchanging bronchi (parabronchi), whereas in the lungs of mammals and presumably other vertebrates, air moves tidally into and out of terminal gas-exchange structures, which are cul-de-sacs. Unidirectional flow purportedly depends on bellowslike ventilation by air sacs and may have evolved to meet the high aerobic demands of sustained flight. Here, we show that air flows unidirectionally through parabronchi in the lungs of the American alligator, an amphibious ectotherm without air sacs, which suggests that this pattern dates back to the basal archosaurs of the Triassic and may have been present in their nondinosaur descendants (phytosaurs, aetosaurs, rauisuchians, crocodylomorphs, and pterosaurs) as well as in dinosaurs.
authors.affiliation: Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, UT 84112, USA. cg.frmr@gmail.com
authors.forename: C G
authors.initials: CG
authors.lastname: Farmer
authors.forename: Kent
authors.initials: K
authors.lastname: Sanders
mesh_terms: D000489:Alligators and Crocodiles / Q000033:anatomy & histology / Q000502:physiology*; D000818:Animals; D005075:Biological Evolution; D001980:Bronchi / Q000033:anatomy & histology / Q000502:physiology*; D025061:Dinosaurs / Q000502:physiology; D008168:Lung / Q000033:anatomy & histology / Q000502:physiology*; D012123:Pulmonary Ventilation; D012119:Respiration