Biostratigraphic and macroevolutionary study of Antartic Neogene rediolarian faunas
Final Report Abstract
Fossils of single-celled plankton are extremely abundant and well preserved in deep-sea sediments, which also preserve very detailed records of past ocean environmental change. The distribution of fossil species over time can be used to study both evolution and how the environment regulates biologic diversity. Our study looked at 1) the Neogene (last ca 20 million years) record of radiolarians, one common group of marine microfossils, in sediments from the Southern Ocean; and 2) the global Cenozoic (last ca 60 million years) record of planktonic marine diatoms, using data already in the published literature. For radiolarians we made new observations of all species seen in a series of samples (ca 700,000 individuals counted, over 100 species new to science identified and described), and used this data to calculate the diversity history. By comparing our result to estimates made only from previously published data, which is relatively incomplete and of uneven quality, we were able to identify where existing methods for calculating diversity from published data needed improvement. We were also able to link changes in species abundances around 8 million years ago to changes in the Southern Ocean environment. We documented as well a major extinction of radiolarians around 5 million years ago, possibly associated with a global warming interval that began about then. Our diatom analyses built on our insights from our radiolarian study, and developed new methods to better reconstruct the original diversity history from available published data. We found that our new estimates matched well those that we calculated from an as yet unpublished independent catalog of fossil diatom species. We then compared our new diatom diversity estimate to the history of ocean environmental change, and showed that they are very highly correlated: diatom diversity increased over time as global climate cooled. This result is important for two reasons. First, evolutionary biology has long debated whether environmental change or biologic interactions are primarily responsible for evolution. Our result is a very clear example of primary environmental control over larger-scale evolutionary pattern. Second, our result shows that diatom diversity can be expected to significantly decrease if global climate becomes too warm (i.e., many species would be expected to become extinct), and that the tipping point for such behavior is close to the climate state projected for the next centuries due to global warming.
Publications
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2011. The deep-sea microfossil record of macroevolutionary change in plankton and its study. p. 141–66. In Smith, A., and A. McGowan [eds.] Comparing the Geological and Fossil Records: Implications for Biodiversity Studies. Special Publications, volume 358. The Geological Society
Lazarus, D.
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2012. New species of Neogene radiolarians from the Southern Ocean. Journal of Micropalaentology 31: 29–52
Renaudie, J., and D. Lazarus
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2012. Pacman profiling: a simple procedure to identify stratigraphic outliers in high density deep-sea microfossil data. Paleobiology 38: 144–61
Lazarus, D., M. Weinkauf, and P. Diver
