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Abstract Detail

Paleobotanical Section

Strömberg, Caroline A E [1], Wing, Scott L. [1], Hickey, L. J. [2], Behrensmeyer, Anna K [1], Tiver, Fleur [3], Willis, Brian J [4], Burnham, Robyn [5].

The ecological role of angiosperms in Late Cretaceous vegetation at Big Cedar Ridge, Wyoming.

Over the last 15 years new fossil and molecular data have reinforced the idea that angiosperms radiated rapidly in the mid-Cretaceous. By the early Maastrichtian most ordinal-level lineages had appeared, and flowering plants made up the vast majority of plant diversity in terrestrial ecosystems. However, the ecological factors that allowed the diversification of flowering plants are not well known, and their role in Late Cretaceous vegetation is poorly understood.
The ecological roles of early angiosperms can be reconstructed better with detailed information about their distribution in plant communities and along environmental resource gradients. The early Maastrichtian flora at Big Cedar Ridge (BCR), Wyoming, presents a rare opportunity for such a study. Plant fossils are preserved in situ at the base of a bentonitic tuff lying above a thin paleosol. The 4 km long exposure provides a snapshot of a Late Cretaceous deltaic coastal plain landscape. We recorded sedimentological data and quantified abundance of all plant fossils from 100 sites along the BCR outcrop in order to understand vegetation structure and the distribution of angiosperms.
The analysis showed that vegetation at BCR was dominated by ferns, cycads, conifers, and palmettos, with rare herbaceous dicotyledons (12% of the identified cover). The distribution and abundance of these plants, however, were strongly tied to microhabitat as inferred from paleosol features and lateral variations in lithofacies. Relatively species poor fern-cycad or palm-conifer-fern communities developed on peaty, mature soils. In contrast, dicotyledons, comprising 61% of species overall, were only abundant (>30% of cover) in local patches with low soil carbon and evidence for physical disturbance in the form of channel deposition that occurred just prior to the preserving event. The rarity of dicotyledons outside of such restricted streamside microhabitats is consistent with dispersed populations for which insect pollination may have been important.

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1 - National Museum of Natural History, Smithsonian Institution, Department of Paleobiology, Mrc 121, Washington, DC, 20560, USA
2 - Yale University, Department of Geology & Geophysics, Yale Station, P.O. Box 208109, New Haven, Connecticut, 06520-8109, USA
3 - University of South Australia, Division of Information Technology, Engineering and the Environment, School of Natural and Built Environments, Mawson Lakes Campus, Mawson Lakes, South Australia, 5095, Australia
4 - Chevron Energy Technology Company, Shallow Marine Stratigraphy, 1500 Louisiana Street, Houston, TX, 77002, USA
5 - University of Michigan, Museum of Paleontology, 1109 Geddes Avenue, Ann Arbor, Michigan, 48109-1079, USA

Upper Cretaceous
early angiosperms
North America.

Presentation Type: Oral Paper:Papers for Sections
Session: CP31
Location: Lake Erie/Hilton
Date: Tuesday, July 10th, 2007
Time: 11:00 AM
Number: CP31004
Abstract ID:2216

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