XVI International Botanical Congess

Typical Late Eocene-Early Oligocene fossil floras of North America and Europe record lowland depositional sites associated with marginal marine and interior lacustrine environments. In contrast, some western North American sites document upland/montane ecosystems, preserved as a consequence of local volcanism. Palynological and megafossil assemblages such as Florissant, Creede (Colorado), Copper Basin, Bull Run (Nevada),and Thunder Mountain (Idaho) provide insights into communities of cooler/drier aspect,compared with lowland assemblages. Such floras require careful analysis however, for like Neogene assemblages from the region, vegetation dynamics driven by ecological factors such as fire and volcanism may be mistaken for climate-induced changes in the source vegetation.