Biodiversity at an epoch boundary: Paleocene-Eocene mammals and continental paleoclimates

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Oceanic sediments indicate that the Paleocene-Eocene transition involved global warming, with a reduced latitudinal temperature gradient, ocean-dominated poleward heat transport, and weak atmospheric circulation. Continental climates should be warm but highly seasonal under these conditions, but Eocene continental floras are usually interpreted as non-deciduous and non-seasonal. Independent evidence of climate and seasonality is sought from fossil mammals. Twenty-five large faunal samples are available from successive intervals in one stratigrpahic section in northwestern Wyoming, and intensive collecting will make at least 15 more samples large. These 40 faunal samples span the interval from ca.58 to 56 Ma-- the interval including the Paleocene-Eocene epoch boundary and earliest Eocene warming event. Temporal spacing of samples is comparable to that in ODP cores. Analysis of species richness, species diversity,k rank abundance of species-per-family, body size of the largest mammal, and rank-body-size faunal structure should provide a record of change in continental paleotemperature, moisture and forest openness for the 2 m.y. study interval. Spacing of dentinal laminae in tusks of Coryphodon is being investigated as a source of new information on seasonality.