Abstract Detail


Hamersma, Ashley [1], Manchester, Steven [2].

The Beaver Creek Flora, a late-Eocene or early Oligocene Flora of Southwestern Montana: A Diverse Window into the Changing Environments of the North American West.

The Beaver Creek florule is an exquisitely-preserved fossil site located in Powell County, southwestern Montana, in the northern U.S. Rocky Mountains. It comprises well-preserved adpression fossils of leaves and reproductive structures in lacustrine shales, and represents a very different landscape from the conifer-dominated areas of today. Collections have been made over the past several decades, and from them 20 families and 26 genera have so far been identified (including Anacardiaceae: Rhus, Araliaceae, Betulaceae: Asterocarpinus, Berberidaceae: Mahonia, Caprifoliaceae: Diplodipelta; Cercidiphyllaceae: Cercidophyllum; Cupressaceae: Glyptostrobus, Cupressaceae spp.; Equisetaceae, Fabaceae: Cercis; Fagaceae: Quercus, Ginkgoaceae, Juglandaceae, Lauraceae: Lindera, Malvaceae: Tilia, Plafkeria; Pinaceae: Pinus, Abies; Rhamnaceae, Rosaceae: Amelanchier, Rosa, Chamaebatia, Cercocarpus, Sorbus; Salicaceae: Populus; Sapindaceae: Acer; Simaroubaceae: Ailanthus; Ulmaceae: Ulmus, Zelkova). Many of these genera are no longer present in modern local vegetation (e.g., Ginkgo, Lindera, Ulmus) and many described genera are characterized today by a strong disjunct east-Asian, east-North American distribution pattern (e.g., Cercidophyllum, Ailanthus, Ginkgo). Particularly diverse elements include the Rosaceae, with 5 genera represented, and Mahonia, with at least three species present. Floristic elements are overall deciduous with the exception of Mahonia, Pinus, and Abies. Suitable materials for radiometric dating have not been recovered, but based on age constraints estimated from present taxa (e.g., Asterocarpinus, Ailanthus, Beckerospermum, Diplodipelta reniptera) we estimate an age of late Eocene or early Oligocene. Previous dating based on proximal faunal fossil localities estimated the age of the Beaver Creek florule to be part of the Cabbage Patch formation (late Oligocene - early Miocene). In addition to floral fossils, extensive insect damage has been observed along with occasional well-preserved insects. Description of this flora facilitates discussion of paleoclimatic and biogeographical change in the northern U.S. Rocky Mountains in Montana during a period of highly variable climate, and adds to the paleobotanical record of the area, with potential implications for the timing and processes of floristic disjunctions between North America and eastern Asia.

1 - University of Florida, Biology, 876 Newell Drive, Gainesville, FL, 32611, USA
2 - Florida Museum Of Natural History, Dickinson Hall, Museum Rd & Newell Dr., Gainesville, FL, 32611, United States


Presentation Type: Oral Paper
Number: PB1006
Abstract ID:527
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award

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