MONOCOT DIVERSITY DURING EOCENE WARM CLIMATES

Monocot flowering plants comprise ~22% of flowering plant diversity, and yet are relatively underrepresented in the fossil record. However, their study is important because many monocots are economically important (e.g., food from grasses such as wheat, rice, corn) as well as being key or indicative taxa of certain ecosystems (e.g., wetlands, grasslands, tropical climates characterized by palms and gingers). The Eocene was a period of global warm climates, and there is a rich paleobotanical record that supports this. Here, the monocot component of the Okanagan Highlands fossil floras are examined and compared with other global contemporaneous floras to examine how the monocots contribute to our understanding of Eocene environments in northern North America, and changes in floristic diversity. Floras from the Okanagan Highlands date from about 52-48.7 Ma and include both compression sites (e.g., Republic, McAbee, Horsefly, Quilchena, and Falkland localities) and a permineralized site (Princeton Chert). Monocots typically form less than 3% of total diversity in the compression floras, but comprise ca. 20% of species diversity in the Princeton Chert. Many of the fossils preserved at the compression sites show affinities to Poales (grasses and sedges) while in the Princeton Chert Alismatales (water plantains), Arecaceae (palms), and Liliales (lilies) are also represented. In contemporaneous early-middle Eocene floras the monocots form a similar proportion of the assemblage at the Messel and Clarno Nut beds localities, and are a slightly larger component of the London Clay (7%). However these are quite different from the Okanagan Highlands floras in having a more significant tropical component (e.g., 22 palm species in the London Clay; Cyclanthaceae and Arecales in Messel, and Arecales and Musaceae in Clarno). Overall, preserved monocot diversity is less than expected when compared to modern floras (up to ~30% of species) even during this greenhouse period, but the presence of elements such as palms and aquatic monocots reinforce the interpretation of warm and moist global climates in the early-middle Eocene.