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Abundance as a factor in background extinction: bivalves from the Choptank Formation (Miocene) of Maryland
Pennington, Zachary Everett
Pennington, Zachary Everett
Abstract
Using bivalve data from the middle Miocene, I explored the relationship between abundance and survivorship. Samples were collected from the Drumcliff Member of the Choptank Formation (12Ma— 10Ma). Abundance was measured using the metrics of raw, rank, percent, total abundance, and average abundance. Raw data were collected by counting the number of hinges and dividing by two. Stratigraphic duration served as a proxy for extinction. Stratigraphic ranges were collected from the literature. Duration was categorized in two ways: categorical of long versus short and duration in millions of years. Variance data were calculated to test for survivorship versus variability. Spearman or Pearson tests were used depending on normality to test the relationship between abundance and duration in millions of years. Mann-Whitney and t-tests were used to test the relationship between abundance and categorical duration. No statistically significant relationships were found. A vague negative correlation was found, implying that the longer extant species have a lower abundance, but this relationship was not statistically significant. In conclusion, abundance does not play a large role in extinction in bivalves during the Miocene.
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2006-01-01
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Geology