PNB 2250 Lecture Notes - Lecture 6: Buccal Pumping, Swim Bladder, Bird Anatomy
12 Sep 2016
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Document Summary
Driving forces of evolution: life developed in the ocean first. Fresh and salt water: the drive toward terrestrial existence. Realization gills were poorly suited for terrestrial life. Timeline: air breathing fish appeared approximately 430 million years ago, occurred long before appearance of amphibians, appeared several times in fossil record, came up with great solutions to similar problems. Evidence: the ability to gulp air came first. Requirements for air breathers: ability to control muscles to gulp air (not a trivial issue, development of a sac, formation of pharynx. Needed where gas exchange cannot take place: co-development of surfactant. Water must always be present: changes in patterns of blood flow to the developing air sac. Coordinating flow with circulation: further development of a 2-cycle or 4-cycle breather. Other considerations: lungs in fish changes buoyancy. Makes it hard to stay away from surface: energy required to swim to surface to gulp air is significant. Most likely developed in warm, shallow water.
