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Sexual Dimorphism and species selection in Late Cretaceous fossil ostracodes from the U.S. Gulf Coastal Plain
Solon, Christine M.
Solon, Christine M.
Abstract
Species level selection, a variant of natural selection in which entire species, as opposed to individual organisms, are selected for or against, is a relatively under-studied process that may play an important role in evolution. Recent studies have used sexual dimorphism to examine potential instances of species selection because it is a trait that is both determined by heritable physical characteristics and occurs solely at the species level. The results of such studies, typically conducted on modern birds, have varied; in some instances the data have supported a correlation between dimorphism and extinction. In this study, we will determine if sexual size dimorphism is correlated with extinction or origination in Late Cretaceous ostracodes from the U.S. Gulf Coastal Plain, and whether the magnitude of dimorphism relates to the rates of extinction and origination in these species. We examined 33 species of ostracodes collected from samples of Late Cretaceous sediment in Alabama. Male ostracodes, because of their very large sperm and bulky copulatory apparatus, tend to be more elongate than females. We modeled body size data as a mixture of two bivariate normal distributions, one for each sex, and used the Mahalanobis distance between males and females to quantify the magnitude of sexual dimorphism for each species. When we compared the stratigraphic ranges of each clade in the Gulf Coastal Plain, we found no relationship between sexual dimorphism, body size, or taxonomic family and extinction or origination rates.
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2012-01-01
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Geology