Paleoatomospheric oxygen estimates based on Berner et al. 2007

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Today, the Earth's atmosphere contains 21% oxygen, however, this has not always been the case. Throughout our planet's history, fluctuations in the Earth's atmosphere have both influence and been influenced by biological life.  About 280 million years ago, oxygen levels peaked at 30-35%, which correlates with an explosion in the diversity and radiation of tetrapods (four-legged animals) in the fossil record. Graham et al. 1995 hypothesized that increased oxygen availability in the atmosphere may have enhanced early tetrapod activity on land and aided in their expansion.

This study set out to test this hypothesis by using mudskippers, an amphibious fish, to model the effects of oxygen on the terrestrial performance on early land vertebrates.  These fish were exercised on a treadmill under different oxygen levels that mimicked those  that occured during the Paleozoic.


With increased oxygen, mudskippers were able to both run longer and recover faster from exercise. These findings suggest that early tetrapods also likely benefited from elevated oxygen levels during the Permian. Increased aerobic performance may have enhanced ability to capture prey and avoid predators, and ultimately aid in the survival and establishment of tetrapods beyond the waters edge.

This work has resulted in the following publication and cover:

Cover image: The Japanese mudskipper (Periophthalmus modestus) is an amphibious fish known for its burrow building and
highly active behavior above the water line. Mudskippers have a mainly Indo-Pacific distribution and possess numerous
adaptions for life on land including fused lamella, highly vascularized epithelial lining inside the mouth and along the body skin
for respiration, flattened lenses for visual acuity in air, and the ability to hear airborne sounds. The unique locomotive behavior
of these fish on land known as ‘‘crutching’’ involves the use a fused pelvic girdle and pectoral fins. Photo by Corey J. Jew,
‘‘Atmospheric Oxygen Levels Affect Mudskipper Terrestrial Performance: Implications for Early Tetrapods.’’