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Abstract Detail

Themes of land plant evolution, a celebration of the contributions of Leo J. Hickey

Wing, Scott [1], Hickey, Leo [2], Stromberg, Caroline [3].

Dominance and diversity in a Late Cretaceous fern prairie at Big Cedar Ridge, Wyoming.

The Big Cedar Ridge (BCR) flora is preserved largely as in situ compression fossils at the base of a volcanic ash exposed laterally for ~4 km. The ash, in the Meeteetse Fm., has been dated at ~73 Ma (late Campanian). Intensive collecting yielded ~162 leaf taxa: ~67% angiosperms, ~23% cryptogams, ~7% conifers, and 4% cyadophytes. Abundances of species quantified with a line-intercept method revealed five floral associations, three dominated by pteridophytes. One fern association occurred on peat soils and was dominated by several species in Gleicheniales including one of Dipteris (Hausmannia). A second association, on less organic-rich substrates in proximity to paleochannel margins, was dominated by Sectilopteris psilotoides (Schizaeales). The third fern-dominated association, on muddy soils and interspersed with patches of palms, was dominated by Anemia fremontii (Anemiaceae, Schizaeales). Twenty-four of 34 pteridophyte species at BCR can be assigned to an order. Eight species (33%) belonging to Polypodiales account for <10% of pteridophyte cover, and only one, Allantoidiopsis (Dryopteridaceae) is common. There are six species of Gleicheniales, including two Dipteridaceae, three Gleicheniaceae, and one Matoniaceae. Four of the species of Gleicheniales are abundant, each representing more than 3% of total identified plant cover. In aggregate Gleicheniales represent 25% of pteridophyte diversity and 40% of pteridophyte cover. Four species are assigned to Schizaeales, accounting for 17% of pteridophyte species and >43% of pteridophyte cover. The high abundance of Schizaeales results from dominance by, Anemia fremontii (Anemiaceae), the second-most abundant species (14% of total identified cover), and Sectilopteris psilotoides (Schizaeaceae?), which was highly abundant on recently disturbed organic-rich soils (>6% of total identified cover). Other pteridophytes identifiable to order include two species of Osmundales, one of which is moderately abundant (>1% of total cover), three rare species of Hymenophyllales, and one rare species of floating aquatic, probably belonging to Salviniales. The vegetational dominants of the “fern prairies” at BCR belonged to non-polypod orders, which together comprised two-thirds of pteridophyte diversity. Polypodiales, in contrast, were significant in diversity (one-third of species) but minor in biomass. These results are preliminary because 10 of the 34 pteridophyte species remain unassigned to order, however, none of the unassigned species are abundant, so they would not substantially increase the abundance of Polypodiales. The combination of high diversity with low dominance seen in Polypodiales is also found in dicotyledonous angiosperms at BCR. Does high diversity generally precede high dominance in rapidly radiating lineages of plants?

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Related Links:

1 - Smithsonian Institution, Dept. of Paleobiology NHB 121, PO Box 37012, WASHINGTON, DC, 20013-7012, USA
2 - Yale University, Dept. of Geology and Geophysics, P.O. Box 208109, New Haven, CT, 06520-8109, USA
3 - University of Washington, Department of Paleobotany, 24 Kincaid Hall, Box 351800, Seattle, WA, 98195-1800, USA


Presentation Type: Symposium or Colloquium Presentation
Session: C6
Location: Belle-Chasse/Riverside Hilton
Date: Tuesday, July 30th, 2013
Time: 2:45 PM
Number: C6005
Abstract ID:354
Candidate for Awards:None

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