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Abstract Detail

Paleobotanical Section

Allen, Sarah [1].

Leaf fossils from the Blue Rim flora of the Eocene Bridger Formation, southwestern Wyoming.

The early Eocene (~49.5 Ma) Bridger Formation crops out along the Blue Rim escarpment in southwestern Wyoming and includes abundant, well-preserved plant fossils collectively referred to as the Blue Rim flora. The fossils include wood, reproductive structures, dispersed pollen, and numerous leaf morphotypes. Leaf macrofossils were collected from two distinct horizons at Blue Rim, separated stratigraphically by about 43 meters. The leaf flora is composed of ferns including Lygodium kaulfussi Heer, Acrostichum hesperium (Lesquereux) MacGinitie, and Asplenium delicatula (Brown) MacGinitie. In the lower horizon, Lygodium kaulfussi, a climbing fern in the Schizaeaceae, is by far the most common plant fossil found at Blue Rim. No gymnosperms have been recovered from the macroflora, although they are present in the microflora. Angiosperms are well represented by eudicots; monocots are rare. Fossil leaf morphotypes at Blue Rim previously documented in the regional flora (Green River and Aycross Formations) include: “Aleurites” fremontensis (Berry) MacGinitie, “Cedrela” schimperi (Lesquereux) MacGinitie, Cedrelospermum Saporta, Grewiopsis Saporta, Macginitiea Wolfe and Wehr, Platanus L., Populus L., Rhus nigricans (Lesquereux) Knowlton, “Serjania” rara MacGinitie, and Syzygioides Manchester, Dilcher et Wing. A new species of Icacinaceae is also recognized, which co-occurs with two icacinaceous fruit types and is likely related to the extant genus Iodes Blume. Present collections from the Blue Rim flora include additional fossil leaf morphotypes with unknown taxonomic affinities. A field census of the dicotyledonous morphotypes demonstrates clear differences in species composition between select quarries from different stratigraphic levels. Populus cinnamomoides (Lesquereux) MacGinitie predominates among the angiosperm taxa from the original quarry site in the lower horizon (~39 percent). Specimens assignable to “Cedrela” schimperi and “Serjania” rara comprise an additional ~43% of this lower flora. In contrast, Populus cinnamomoides is sparse and Macginitiea and other unidentified morphotypes are more common in the main upper horizon quarry. These differences in species composition and diversity may be due to variations in the depositional environment or may represent true changes in the flora of this basin through time. In addition, the leaf flora provides opportunities to estimate the paleoclimate using both physiognomic and nearest living relative approaches.

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1 - University of Florida, Department of Biology, P.O Box 118525, Gainesville, FL, 32611, USA

leaf fossils
Bridger Formation

Presentation Type: Oral Paper:Papers for Sections
Session: 15
Location: Salon 5/The Shaw Conference Centre
Date: Monday, July 27th, 2015
Time: 1:30 PM
Number: 15001
Abstract ID:1071
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award

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