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Jocelyn Sessa Brian T. Huber, Ph.D. "'When I use a word,' Humpty Dumpty said in rather a scornful tone, 'it means just what I choose it to mean - neither more nor less.' 'The question is,' said Alice, 'whether you can make words mean so many different things.' 'The question is,' said Humpty Dumpty, 'which is to be master, you or words, - that's all.' (Through the Looking Glass) So what's a species anyway?" |
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Middle Cretaceous paleoclimatic variation during the evolution of the planktic foraminifer species, Costellagerina libyca. Foraminifera are single celled, amoebae-like organisms that are found in a variety of salt and fresh water environments, at many different depths, and from the equator to the poles. Many foraminifera secrete shells called tests, which are composed of calcite. Analysis of the composition of tests can give information concerning the climate the foraminifera once inhabited. Specifically, the isotopic analysis of carbon and oxygen ratios preserved in tests can be used to infer temperature and depth. In this investigation, foraminifera from mid-Cretaceous time (98-101 million years ago) were studied from two locations in the Atlantic Ocean. During Cretaceous time warm temperatures prevailed. One species in particular, C. libyca, displays very warm temperature values, indicating it existed in warm surface waters. Previous authors have suggested C. libyca was a descendant of a foraminifer species called Hedbergella portsdownensis. By using isotopic data obtained from tests of both H. portsdownensis and C. libyca, it was discovered that the two inhabit very different environments. This suggests that H. portsdownensis is not the ancestor of C. libyca. This study also examined changes occurring within the world's ocean 100 million years ago. By evaluating the different types of foraminifera found at each sample level conditions, such as a rise or fall in sea level, can be detected. The findings of this study indicate a change in the world's oceans occurred during this time. A rise in the amount of carbon stored within the ocean correlates with a period of anomalously warm temperatures. These conditions seem to have triggered the evolution of C. libyca from an as of yet unknown ancestor. This research project has created exciting new questions concerning the true ancestor of C. libyca, as well as what caused such a variation in Cretaceous climate, and further research will be conducted in order to answer these and other questions. This research was supported by a grant from the National Science Foundation Research Experiences for Undergraduates program, Award Number DBI-9820303. |
