Biotic evolution in Plio-Pleistocene marine environments of tropical America: Systematic, phylogenetic, and stable isotope investigations of the Muricidae (Mollusca: Gastropoda)

This dissertation considers the biotic impact of largescale environmental change through a detailed investigation of the Plio-Pleistocene record of marine gastropods of the family Muricidae from nearshore deposits of Florida and elsewhere in tropical America. Its primary contribution to theory and method in paleobiology is its emphasis on documenting biotic changes in the fossil record from the perspective of life history strategies using stable isotope sclerochronology.; One of the central contentions of this work is that life history strategies can provide a more sensitive and more informative measure of biotic changes than traditional sources of data in paleobiology, such as morphology and taxonomic diversity. Stable isotope sclerochronology of four species of marine molluscs that survived the Pleistocene ice ages revealed that despite an absence of directional change in form within species, life history strategies evolved in parallel as predicted by neo-Darwinian models of evolution. Evolutionarily significant responses to environmental change may be morphologically cryptic and quantifiable only within a life history framework.; Stable isotope sclerochronology was also used to document changes in the distribution of rapid and slow maturing species of the Urosalpinx genus group (Mariasalpinx, Trossulasalpinx, Urosalpinx, Vokesinotus) of predatory muricid gastropods across two regional mass extinction horizons in the Plio-Pleistocene of Florida. Taxonomic datasets reveal the presence of these intervals of extinction but cannot resolve their causes. Analyses revealed that decline of populations in the Pliocene was strongly influenced by variation in age at first reproduction. The rules of survivorship also changed from one horizon to the next, suggesting a shift in the primary causal mechanisms driving extinctions within the Pliocene. Previous studies had assumed only one primary cause. The specific selective patterns documented are consistent with extinctions due to Northern Hemisphere Glaciation at the first horizon (ca. 2.5 Ma) followed by extinctions due to planktonic productivity decline at the second (ca. 1.8 Ma). Similar patterns of life history change were inferred from a phylogenetic analysis and morphological comparisons of species belonging to the genus Eupleura, which was decimated by extinctions throughout the Atlantic.