MODERN ENVIRONMENTAL ANALOGUES AND MORPHOLOGICAL LEAF FEATURES ARE IMPORTANT IN UNDERSTANDING PALEOGENE MAMMAL HERBIVORY

Morphological traits of living plants can serve as proxies for modern environments. Such traits as leaf physiognomy, wood anatomy and stomatal index document features indicative of a given biome. These proxies have been used by paleobotanists to interpret paleoclimate and paleoecology of fossil assemblages. Similarly biotic interactions have been assessed through such proxies as fungal symbioses, insect herbivory and mammal dietary analyses based on dental morphology. Whereas studies of herbivory have focused largely on plant influence on animals, the plant's response to herbivores would likewise be reflected in its leaf morphology. For example, the co-occurrence of large mammalian herbivores and plant fossils with defense morphologies would be of particular interest in reconstructing Paleogene communities. Over the last five years, we have begun comparison of the extant biota of the Virunga Mountains in eastern central Africa to understand past mammal herbivory. The Virungas serve as an analogue for early Eocene upland lacustrine environments of the Okanogan Highlands, British Columbia, Canada and Republic, WA, USA. Plants in the Virungas today have survived strong selective pressure from megafauna. We would expect to find indications of similar foliar responses to herbivory in the fossil record. To date we have documented stinging trichomes in fossil leaves assignable to tribe Urticeae (Urticaceae). Also known from the same localities are sumac leaves (Rhus Anacardiaceae) that show distinctive glands that document the Paleogene presence of foliar irritants, like those of the modern-day relative poison ivy [Toxicodendron radicans (L.) Kuntze]. Previous studies have demonstrated the coevolution of plant mechanical defenses with frugivorous. The coexistence of folivores with leaves with distinctive defense structures such as stinging trichomes provide us with valuable characters and increase our understanding of plant responses to megafauna during the Paleogene.