The Mahenge site consists of crater lake deposits formed subsequent to a kimberlite eruption dated at approximately 46 Ma. The sediments contain plant fossils dominated by leaf remains, with a smaller number of seeds and fruits, as well as abundant fish remains, and other vertebrates including a bat and frog. This locality provides a unique opportunity to evaluate an environment at a tropical low latitude in the Middle Eocene, a time of warmth at high latitudes and unresolved global circulation patterns. A minimum of 20 species (based on leaf morphotypes) is present among the approximately 200 plant specimens, which include at least 7 species in the Leguminosae family. Among these is the genus Acacia, which today is limited to hot or warm, seasonally dry environments. A preliminary analysis of leaf area, which is positively correlated with mean annual and wet season precipitation, indicates that rainfall at Mahenge was approximately 700 mm/year, or about 400mm/yr less than what would be required to support tropical forest vegetation today. The Mahenge flora provides a first data point for paleoclimate in the Eocene of tropical Africa and the paleovegetation reconstruction fits well within the larger framework established by a limited number of palynological and fossil wood records from North and West Africa. These have been interpreted as indicating relatively low diversity communities in the Early to Middle Eocene, followed by the initial development of lowland forest represented by increasing diversity in the Late Eocene and Oligocene. Our interpretation ofthe Mahenge paleocommunity is concordant with the hypothesis that forest vegetation was not yet established within the tropical belt of Africa 46 million years ago.

Key words: Africa, African paleobotany, Eocene, Tanzania paleoclimate