Oral Paper

         Paleobotany

Update on the paleobotany of the Upper Pennsylvanian Dennis Formation in Missouri and Kansas, USA

Presenting Author
Nathan Jud
Description
Plant fossil assemblages from the Upper Pennsylvanian Dennis Formation in Missouri and Kansas are dominated by remains of cordaitaleans and medullosan pteridosperms, but the flora has never been treated in detail. Description of these fossils helps to fill a geographic gap between the Illinois Basin (Bond Formation) to the east and the early Missourian of New Mexico (Tinajas Member, Atrasado Formation) to the west. Locally, they also fill a temporal gap between the wetter Desmoinesian coal floras of Missouri and Kansas and the drier, later Late Pennsylvanian conifer-dominated floras at Garnett and Hamilton, Kansas. Macrofossils include Cordaites spp. “Neuropteris” lindahli, Neuropteris hastata, Macroneuropteris scheuchzeri, Cyclopteris sp., and permineralized wood. The wood has the following combination of characters: tracheids with closely spaced alternate circular bordered pits in 1–2(3) series on the radial walls, rays 1–21 cells high and uniseriate with local biseriate portions, cross-fields with 1–2 cupressoid oculipores, and little to no axial parenchyma. One specimen with primary tissues preserved has a wide (~18 mm by 8 mm) hollow pith without septae surrounded by >46 mesarch cauline bundles. The palynoflora includes monosaccate and bisaccate grains typical of cordaitaleans and early conifers, monolete spores typical of sphenophytes, and trilete spores of ferns and lycophytes. These fossils provide direct evidence of colonization of the region by drought-tolerant (dryland) Cordaites-pteridosperm forests during the early Missourian when the sea level was low.