THE CLAIBORNE AND CATAHOULA FORMATIONS, SIGNIFICANT FLORAS FROM THE MISSISSIPPIAN EMBAYMENT

One of the best records of late Eocene-Oligocene floral transition in North America comes from the Mississippian Embayment. Of the many floras initially surveyed by Berry (1916-1941), two have provided the best glimpses of this transition. The middle Eocene Claiborne Formation was investigated in detail by Dilcher and colleagues primarily from the 1960s-1980s and was a major focal point of his research program at Indiana University. Over 30 megafossil genera within 15 families were described in this flora dominated by lauraceous leaves, castaneoid and transitional oaks and representatives of all three major groups of legumes. Like the Claiborne, the Catahoula is rich in legumes, transitional oaks and other Fagaceae, however it lacks abundant Lauraceae. It is the Catahoula that provides us with critical information about the early evolution of Fagaceae. Both intermediate and trigonobalanoid oaks are known from pollen-bearing catkins, and these co-occur with modern-appearing black oak leaves and white oak acorns. One intriguing cupulate husk from both the Claiborne and Catahula localities appears to have affinities to Fagaceae, possibly Castanopsis. The two floras are critical to understanding the evolution of characters within the Fagaceae and other important modern angiosperm groups such as the legumes. Additionally, together these floras provide important documentation for tracking the role of the Mississippian Embayment as a corridor for plant migration in North America.