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Oxygen Levels And Alligator Eggs


New Haven, Conn. -- The development of bone structures in alligator eggs
raised under varying oxygen concentrations creates a link to fossil
records of the evolution of vertebrates and prehistoric atmospheric oxygen
concentrations, according to a paper to be presented at the Earth System
Processes 2 meeting in Alberta, Canada.

"Alligator eggs are an ideal self-contained unit for studying the effects
of oxygen on development -- they have a limited food source in the yolk
and they are incubated in their nesting material at a constant temperature
of 89F and 100 percent relative humidity," said John Vanden Brooks, a
graduate student in the Department of Geology and Geophysics at Yale
University. He noted that large-scale changes in atmospheric partial
oxygen pressure would have had wide-ranging effects on vertebrate
evolution and development throughout geologic time.
His mentor, Robert A. Berner, the Alan M. Bateman Professor of Geology and
Geophysics at Yale, characterized the range of atmospheric oxygen levels
over multimillion year times scales, and established an upper value of
about 31 percent oxygen, and a sharp decline near the Permo-Triassic
boundary to about 12 percent. Earth's current atmosphere is about 21
percent oxygen.

"Each clutch contains 30 -- 50 eggs that are laid together, so easy
comparison can be made between sibling eggs raised under different partial
pressures of oxygen," said Vanden Brooks. Studying five different partial
oxygen pressures across this broad range, he found an optimum at 27
percent oxygen. He found that both high and low oxygen levels altered
growth patterns and affected the timing and extent of bone development,
its chemical composition, and mortality of the developing eggs. 
The talk, "Phanerozoic Oxygen Levels and their Effect on Modern Vertebrate
Development" will be presented at the meeting August 8 -- 11 that is
co-sponsored by the Geological Society of America and the Geological
Association of Canada.