Evolution of Marine Mammal Foraging Behavior Based on Ca and C Isotope Ratios in Bioapatite

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Though the trophic structure of marine ecosystems is known to haveincreased in complexity over time, methods of quantifying this change are lacking. The proposedresearch will expand upon promising preliminary work using Ca isotope ratios as paleoecologicalindicators and develop this isotopic system as a proxy for the trophic level of extinct marine mammals.By combining Ca isotope analyses with C isotope ratios, which vary with foraging habitat in marineecosystems, this project will provide a new means to examine the structure of ancient marine vertebrateecosystems. Since the trophic structure of foodwebs has a significant influence on the pathways by whichnutrients and energy move within and between ecosystems, analysis of the Ca isotope composition ofbiogenic hard parts may aid in elucidating how nutrient cycling and energy flow have fluctuated overtime. Furthermore, by expanding current knowledge of how ancient ecosystems functioned and how theydiffered from today s ecosystems, a44Ca measurements can help improve interpretations of how climaticand environmental perturbations have impacted or were impacted by the Earth s biosphere. Ultimately,this project will provide new insight into the evolution of whales, whose from a terrestrial ancestorrepresents one of the most remarkable transitions in the history of life on Earth.Although the ultimate objective of this research is to understand the role of temporal changes inforaging behavior in the evolution of Cetacea (the clade that includes living whales, porpoises, anddolphins), the influence on Ca isotope ratios of factors other than trophic level must be examined first inmodern species before Ca isotope ratios can be applied to extinct species. Samples of marine mammals infour, distantly related groups (sirenians, mustellids, cetaceans, and pinnipeds) will be analyzed as a meansof addressing the impact of phylogenetic history on a44Ca values; the degree of similarity of a44Ca valuesfor species at the same trophic level will verify whether a44Ca values reflect trophic level differencesregardless of evolutionary history. The C isotope composition of each sample will be analyzed as a proxyfor foraging habitat preference; a stronger correlation between a44Ca with trophic level rather than a13Cvalues will indicate that trophic level has a stronger influence on a44Ca values than the foraging habits ofa species. Variation in a44Ca within a single individual will be explored by analyzing the Ca isotopecomposition of multiple skeletal elements from a single individual from each of the four modern groupsof marine mammals sampled. Once the factors influencing a44Ca values in modern marine mammalshave been constrained, the Ca and C isotope composition of Eocene and Oligocene cetacean and sirenianbioapatite will be analyzed to assess the potential of this proxy for paleoecological studies. Thediversification of cetacean feeding strategies in the Oligocene should coincide with a large change ina44Ca and a13C values of cetacean bioapatite, providing a clear signal of whether original a44Ca values canbe preserved and interpreted from the fossil record. Fossil bones of sirenians will also be analyzed as acontrol for potential changes in seawater a44Ca values, since the trophic level of this group has remainedconstant over time and any changes in the a44Ca values of this group will reflect changes in seawatera44Ca values.Broader impacts. The broader impacts of this project are threefold. First, the grant will furtherthe training and development of a recent Ph.D. who will be supported as a postdoc. Under thesupervision of the PIs, this researcher will have primary responsibility for refining the methodologies,acquiring and analyzing the samples, and interpreting and disseminating the results. Second, the researchwill provide a new and potentially powerful paleoecological tool to the broader community that can beapplied to other ancient marine ecosystems and, after further development, may also have applications interrestrial ecosystems. Finally, the results will complement our increasingly detailed knowledge of whaleevolution. Once the proposed research is completed, the ecological and morphological changesassociated with the evolution of whales will be one of the best documented cases of macroevolutionarychange in the vertebrate fossil record. Given the historical place of whale origins in anti-evolutionpolemics, this research will surely have lasting impact in undergraduate and K-12 class rooms.