LATE EOCENE (CHADRONIAN) DICOTYLEDONOUS WOODS FROM NEBRASKA - EVOLUTIONARY AND ECOLOGICAL SIGNIFICANCE

Five types of Late Eocene woods from western Nebraska are described. Three of the woods have an anatomy comparable to extant genera: Robinia (Leguminosae), Zelkova (Ulmaceae), and Prunus s.l. (Rosaceae). The Robinia wood is the earliest wood record for the genus. One wood has a suite of features most similar to that found in the Juglandaceae, but its combination of characters is not diagnostic to tribe. This material indicates that unique character combinations occurred within the Juglandaceae during the Late Eocene. One wood is likely a legume, but it has a combination of features that occur today in at least four other families, and so it is not assigned to a family. As a group these woods indicate that climate in the Late Eocene of Nebraska was seasonal-the Robinia and Zelkova woods are markedly ring porous, the Juglandaceae-like wood is semi-ring porous, the two diffuse porous woods have small diameter vessels and a high vessel density.