Manchester, Steven R. , Wheeler, Elisabeth F. .
Silicified woods from the Early Middle Eocene Bridger Formation in southwestern Wyoming, USA.
THE early middle Eocene flora of Blue Rim, Sweetwater County, Wyoming, known for its impression and compression fossils of leaves, fruits and flowers, also preserves silicified stumps and logs varying from 20 to 55 cm in diameter. Forty-two individuals were sampled from a single stratigraphic level and thin sectioned for anatomical analyses. No conifers or palms were observed, but four diffuse-porous dicotyledonous wood types are distinguishable. The most conspicuous of these is an anacardiaceous wood characterized by vessels solitary and in short radial multiples, abundant tyloses, crowded alternate intervascular pits, simple perforations, heterocellular rays mostly 1- to 2-seriate, with occasional gum canals and crystals. A second wood type has solitary and short radial multiples, crowded alternate intervascular pits, simple perforations, inconspicuous or absent axial parenchyma and 3-seriate homocellular rays. A third type has mostly solitary vessels with scalariform perforations of 10 to 15 bars, vasicentric tracheids, and mainly uniseriate rays—a suite of characters suggesting affinities to Ericaceae or Myrtaceae. The fourth type has vessels solitary and in radial multiples of 2-3, aliform-confluent paratracheal parenchyma, 1-2 seriate rays. This suite of characters is encountered in Oleaceae, Sapindaceae, and Leguminosae. Although the precise affinities of these woods are still under investigation, the Blue Rim assemblage of the Bridger Formation provides a rare opportunity to correlate silicified woods with associated leaf and reproductive structures. These woods are found together with leaves and fruits of Populus cinnamomoides, flowers and fruits of the extinct sapindalean genus Landeenia, fruits of the extinct anacardiaceous genus, Pentoperculum, leaves of the extinct myrtaceous genus Syzygioides, fruits of Celtis and other unknown taxa. Scrambling plants such as Lygodium and Vitis, also known as impression fossils from the same site, may have ascended to the forest canopy as climbers on these trees.
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1 - Florida Museum of Natural History, Dickinson Hall, P.O. Box 117800, Gainesville, Florida, 32611, USA
2 - North Carolina State University, North Carolina State Museum of Natural Sciences, Raleigh, North Carolina, 27601-1029, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Tuesday, August 1st, 2006
Time: 10:30 AM