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Twelve Million Years of Bird History: A Specimen-based Approach to Reconstructing the Late Neogene Bird Communities of California.
California has experienced significant climate change from the onset of the Miocene (~23Ma) to the present. The impact of past climate change is often recorded in the fossil record, and can be revealed by studying how ecological communities change through time. Fossil seabirds are the ideal taxon for studying faunal responses to environmental changes because they are numerous in collections, easily identified from fragmentary remains, and since modern seabirds respond quickly to immediate changes in their environments, we expect the fossil record of seabirds to faithfully represent past environments. The first study to look at fossil seabird diversity through the Tertiary of the North Pacific relied entirely on literature records to describe the appearance and disappearance of seabird species and correlated these patterns to geologic and climatic events. My thesis utilizes an empirical, specimen-based approach to accurately describe the seabird response to climate and tectonic change during ~12 million years of coastal California’s geologic history (middle Miocene to early Pliocene). The foundation of my dataset is a previously unstudied collection of 305 bird specimens from the John D. Cooper Center for Archaeology and Paleontology, representing a relatively complete sequence of strata (Topanga Group, Monterey Formation-equivalent, and Capistrano Formation). Representing the middle Miocene to early Pliocene of Orange County, these strata form the basis for delineating chronostratigraphic bins used for studying the diversity of the fossil seabird community of California. Comparison of this new collection with 378 seabird specimens from three other institutions across California provides a more complete and detailed view of the seabird community during this period. Diversity, taxonomic richness, and relative abundance were examined using quantitative statistical methods to understand the change in seabird populations over time and depth of deposition. Using these statistical techniques, my data show a clear increase of panalcid abundance and decline of sulid abundance that is coincident with global climatic and tectonic changes as well as enhanced nutrient upwelling. Upwelling through this time also accounts for morphological changes in salmon and speciation in marine mammals. In the future, the specimen-based methodology used here can be applied to contemporaneous taxa, such as marine mammals, to quantitatively analyze diversity and relative abundance during the late Neogene and further explore the relationship between physical drivers and faunal change.
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