EPISODIC HYPERTHERMIC DYSOXIA: CAUSE OF THE PERMIAN/TRIASSIC AND TRIASSIC/JURASSIC MASS EXTINCTION EVENTS, AND FOR THE EVOLUTION OF THE SAURISCHIAN/AVIAN RESPIRATORY SYSTEMS

New information on the levels of atmospheric oxygen through the Phanerozoic (Berner and others) indicates that the end of the Permian and end of the Triassic were times of greatly lowered oxygen compared to the present day, equivalent to oxygen content at extant altitudes in excess of 12,000 feet or more (but with normal atmospheric pressure). Here I propose that the combination of low oxygen and repeated short spikes in global temperature caused by methane induced atmospheric greenhouse conditions were the primary causes of the P/T and T/J exinctions. These lowered oxygen levels, which according to the models persisted through the Triassic and into the early Jurassic (with minima at 250 and 200 mya) may as well have been an environmental effect leading to the evolution of the development of bone pneumatization and air sac system found in modern birds and most lineages of saurischian dinoaurs examined to date. New physiological studies of this system in extant birds shows it to be far superior to the respiratory systems of lizards, amphibians, and mammals in surviving at high altitude (and thus lowered oxygen). It also appears that vertebrate lineages with this, then-newly evolved respiratory system, had higher survival rates across the T/J mass exinction interval than did lineages with the air-sac system.