THE MIOCENE MACROFLORA OF THE NORTHERN OGALLALA GROUP, NORTHERN NEBRASKA AND SOUTHERN SOUTH-DAKOTA

The results of the first comprehensive paleobotanical survey of the no rthern portion of the late Miocene Ogallala Group are discussed. Sever al species of fossilized fruiting structures from vascular plants (Ber riochloa, Celtis, Cryptantha, Biorbia, Lithospermum, Eleofimbris, Care x, and Cyperocarpus) in the mid- to late-Miocene are reported. Fewer t axa (12 genera) were found in the South Dakota-northern Nebraska area than have been reported previously (20 genera) from southern Nebraska- Kansas strata in the same formations and approximately the same area o f exposures. Sites of Barstovian age near the Kilgore Flora sire indic ate that grasses were commonly found in the region. The results presen ted here support the hypothesis that grassland savanna vegetation was widely distributed in the northern Great Plains bg the Clarendonian ag a.