| Summary: | Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1989 This work comprises three detailed studies of ontogeny and ecology. In the first chapter, four living species of the ostracode genus Cyprideis were studied both morphologically and ecologically to determine whether differences in age at maturity are correlated with heterochrony as expected; accelerated maturity should yield generalized morphology and small size, while delayed maturity should produce specialized morphology and large size. Two of the four species show the expected pattern, the other two do not. Cyprideis does not support the generalization that life-history evolution causes heterochrony, and casts doubt on the inference of life-history evolution from heterochrony where the data are drawn exclusively from extinct forms. In the second chapter, populations of Globorotalia menardii and G. tumida were subjected to careful morphological analysis; the stable-isotopic composition of the growth stages revealed that both species inhabit the upper fifty meters of the ocean, descending to deeper water (75-l00m) for the emplacement of an enveloping calcite crust. The third chapter shows a simple relationship between proloculus size and rate of chamber expansion in the polar planktonic foraminifer Neogloboquadrina pachyderma. The consequences for morphology of variations in ontogeny can be used to suggest ways of selecting specimens that minimize ontogenetic variations in shell chemistry.
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