TAXODIACEOUS CONIFER REMAINS AT A LATE PALEOCENE VERTEBRATE SITE NEAR MEDORA, NORTH DAKOTA

The Late Paleocene fossil plant sites at Almont and Beicegel Creek, North Dakota contain unusually rich floodplain floras that most likely experienced periodic flooding, but not the long hydroperiods characteristic of swamps. Ginkgo and the Zizyphoides-Nordenskiodia plant appear to have been the dominants at both localities, with other important components including members of Betulaceae, Cornales, Juglandaceae, Myrtaceae, Sapindaceae, and Zingiberales. Based on the excellent preservation of leaves within a silicified mudstone, Almont can be interpreted as a low-energy site, which has been demonstrated to contain relatively rare but well preserved fish, as well as dytiscid beetles. Beicegel Creek plant remains are typically much more fragmented and contain abundant amounts of stem remains and occasional fish scales, suggesting a higher-energy depositional environment. In both sites taxodiaceous conifers are anatomically preserved. Taxodiaceous conifers are also preserved as in situ upright trunks lacking obvious roots in other Paleocene localities of western North Dakota. We now recognize additional anatomically preserved taxodiaceous conifer cones recovered from a Late Paleocene vertebrate site near Medora, North Dakota. The vertebrate site occurs on property managed by the Theodore Roosevelt Medora Foundation and has been actively worked by the North Dakota Geological Survey Paleontological Laboratory and summer dig participants since 2005. Cones occur within a muddy siltstone immediately above a section of 5 cm thick lignitic mudstone rich in remains of champsosaurs, crocodiles, turtles, fish (the same species that occur at Almont), salamanders, and mammals. This fossiliferous layer is 6.5 m above the contact between the Bullion Creek and Sentinel Butte Formations. The occurrence of these bone beds, and the rich array of large vertebrates, suggests a larger wetland with a longer hydroperiod than the wetlands represented by the assemblage of plants and macroinvertebrates found at Almont or Beicegel Creek.