Selected fruits and seeds from the Middle Eocene Claiborne Formation of southeastern North America.

摘要

A selected flora of fruits and seeds from the Middle Eocene Claiborne Formation of southeastern North America was investigated. The fossil specimens studied are part of a diverse flora, primarily of angiosperms, collected from twelve commercial clay pits in Kentucky, Tennessee, and Mississippi thought to be derived from the infilling with clay of abandoned river channels, possibly oxbow lakes. The fifteen species described are all new species and comprise eleven genera, six of which are newly described. Thirteen of the species belong to the following families: Theaceae, Magnoliaceae, Hamamelidaceae, Moraceae, Sapotaceae, and Arecaceae. One additional species may be related to Anacardiaceae of Humiriaceae, and the last species is of unknown angiospermous affinity. Based on anatomical and morphological features of the fossil fruits and seeds, three extant genera (Magnolia, Corylopsis, and Gordonia), seven extinct genera, and one form genus are recognized. These findings agree with studies of western North American and European floras in which a mixture of extant and extinct genera is present during the Eocene. The presence of five species comprising an extant genus Gordonia and two extinct genera, Gordoniopsis and Andrewsiocarpon, in the tribe Gordonieae in the Theaceae suggests that an early radiation had occurred within that tribe by the Middle Eocene. The Claiborne flora shares some elements, including Magnolia, Corylopsis, and Gordonia, with other Northern Hemisphere floras of the early Tertiary boreotropical flora, but also yields several unique elements, including the seven extinct genera described in this work.