2010 GSA Denver Annual Meeting (31 October 3 November 2010)
Paper No. 77-4
Presentation Time: 8:45 AM-9:00 AM


PAYNE, Jonathan L.1, JOST, Adam B.2, OUYANG, Xueying1, SKOTHEIM, Jan M.3, and WANG, Steve C.4, (1) Geological & Environmental Sciences, Stanford University, 450 Serra Mall, Bldg 320, Stanford, CA 94305, jlpayne@stanford.edu, (2) Department of Geological and Environemental Sciences, Stanford University, 450 Serra Mall, Stanford, CA 94305, (3) Department of Biology, Stanford University, Stanford, CA 94305, (4) Mathematics and Statistics, Swarthmore College, 500 College Ave, Swarthmore, PA 19081

Body size correlates with numerous physiological traits and thus influences organism fitness. However, long-term controls on size evolution remain poorly understood because few datasets spans sufficiently long intervals. One proposed controlling factor is variation in atmospheric oxygen, which is widely argued to have influenced size evolution in numerous taxa, notably gigantism in arthropods during the late Paleozoic. In this study, we compiled a comprehensive genus- and species-level size database of foraminifers (marine protists) to enable an extensive analysis of factors influencing size evolution. Foraminifers are an ideal study group because they are present in all Phanerozoic periods and have been diverse and abundant in shallow-marine habitats since Devonian time. We observe significant correlation between foraminiferan size and atmospheric oxygen concentration. Variation in atmospheric oxygen explains one-quarter to one-third of the variation in 95th percentile and median size among taxa. Larger size is associated with higher oxygen concentrations, as predicted by simple physiological models based on changes in the ratio of surface area to volume. Because the oxygen content ocean waters is controlled in part by atmospheric pO2, we interpret the association between foraminiferan size and pO2 to result from a direct physiological effect of oxygen availability. Multiple regression analysis including six other predictors (pCO2, sea level, number of named geological formations, δ18O, δ13C, 87Sr/86Sr) reveals that oxygen is the best predictor of size variation even after controlling for the effects of other variables. 87Sr/86Sr is the only other significant predictor of size in all models, and it explains substantially less variance in size than atmospheric oxygen concentration does. These findings suggest that oxygen availability is one of the most important global influences on foraminiferan size evolution and provides quantitative support for the hypothesis that widespread Permo-Carboniferous gigantism was enabled by high pO2.

2010 GSA Denver Annual Meeting (31 October 3 November 2010)
General Information for this Meeting
Session No. 77
Paleontology IV - Environmental Controls on Ecology and Evolution
Colorado Convention Center: Room 605
8:00 AM-12:00 PM, Monday, 1 November 2010

Geological Society of America Abstracts with Programs, Vol. 42, No. 5, p. 192

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