Recent projections of anthropogenically-influenced climate change have emphasized the importance of understanding how organisms and biotic communities respond to perturbations on both the long and short term. Data from the fossil record can be instrumental in such studies, offering the potential to study the response of ecosystems to protracted climate change impossible to observe on human time scales of only a few years. PIs plan to evaluate the influence of climate on the ecology and evolution of marine mollusk faunas from the U.S. Gulf Coastal Plain during the Paleogene (~65-25 million years ago). Their approach allows them to integrate records of mean annual temperature and seasonality with shifts in diversity, community composition and structure, morphology (shape), and evolution. They are particularly interested in learning whether there is a correlation between the magnitude and direction of climate change and the amount and nature of evolutionary or ecological change, including whether or not there are thresholds of tolerance below which an ecosystem and its component taxa do not respond. PIs will generate the paleoclimate record from the chemistry of fossil mollusks and fish otoliths (ear stones), and paleoecological patterns will arise from a combination of existing museum collections, published literature, and new field sampling of mollusk faunas. Lastly, they will reconstruct evolutionary relationships and trends within two dominant mollusk groups - venericard bivalves and turritelline gastropods - that are characteristic of this region and time, and overlay this information on the temperature and ecologic records for a comprehensive picture of faunal response to climate change. Their research will contribute substantially to knowledge of how biodiversity in sub-tropical settings responds to climate change of varying types and magnitudes.
The broad objective of this project is to explore the relationships between climate change and evolutionary and ecological trends in shallow marine, mollusk-dominated faunas in the US Gulf Coast. The time interval that we studied (roughly 65-30 million years ago, the Paleogene Period) includes the warmest time on our planet in the last 65 million years and the transition toward cooling that resulted in the onset of glaciation in Antarctica. By the year 2100, it is predicted that the climate of the Earth will approach that of the Paleogene. Funding supported both the collection and tabulation of faunal data and the generation and compilation of isotope-based temperature estimates. Faunal data consist of taxon lists for about 4000 species distributed among more than 2200 localities across the Gulf Coast. Data are compiled from at least 40 published references, including our own fieldwork and collection. Roughly one third of localities have abundance data associated with them derived from bulk samples. Data are archived in the Paleobiology Database (a free online resource for both scientists and the public), and all will be freely available following initial publication. Paleoclimate information for the Gulf Coast is derived from stable oxygen isotope analyses of biogenic carbonate, mostly that of mollusks and otoliths (fish ear stones). High-resolution sequential sampling of shells that grow by accretion enable generation of seasonal temperature records, such that summer and winter temperatures are obtained for nearly all stratigraphic intervals sampled. The dataset now includes more than 7500 individual isotope analyses from more than 350 shells spanning 35 million years of time. These data will also be made available following publication. With data collection essentially complete, we are now exploring various methods by which to assess the relationship between faunal and climatic change. Our findings indicate that faunas adapted for warm conditions during the first half of the Paleogene did not suffer lasting effects following the transient, even warmer conditions of the Paleocene-Eocene boundary. Those same faunas, however, experienced a significant increase in extinction rate as temperature declined and seasonality increased. By analogy, one might therefore expect today’s faunas, adapted to the cool conditions of the last few million years, to suffer greater extinction as global temperatures warm beyond those generally experienced on the planet in the last 30 million years.
