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Abstract Detail

Paleobotanical Section

Mack, Nathan G. [1], Tate, Richard W [1], Lindquist, Sarah R. [1], Calder, Vanessa J. [1], Tomescu, Alexandru MF [1].

Searching for structural analogues of early Paleozoic continental thalloid fossils a simple experiment simulating compression fossilization in living organisms.

Thalloid compression fossils preserved in Ordovician and Silurian rocks of the Appalachians include the earliest complex organisms on continents and are crucial in illuminating the origin of land plants. Efforts aimed at resolving the taxonomic affinities of these important fossils are confronted with a challenging combination of preservation of potentially diagnostic anatomical and ultrastructural features, with diagenetic obliteration of other significant characteristics. This combination renders direct comparisons with living organisms ineffective. To bridge the preservational gap, we simulated fossilization by applying compression and heat to organisms from different living groups that could have produced thalloid fossils, and documented the resulting effects on anatomy and ultrastructure. Organisms included in the experiments were cyanobacteria (Nostoc), freshwater algae (Spirogyra), lichens (Parmotrema, Peltigera), bryophytes (Anthoceros, Pellia, Marchantia, Conocephalum), fungi, and marine algae (Mazzaella, Fucus, Ulva). Light- and electron microscopy reveal a broad range of responses to compression and heat. Marine algae are virtually not affected, as is Parmotrema. Pellia, Conocephalum, Marchantia, and Nostoc exhibit moderate effects of compression, with layering of tissues, cells, and other internal structures still recognizable to some extent. At the other end of the spectrum, Peltigera shows some of the most dramatic structural changes due to compression. Spirogyra, Anthoceros and the fungi fall within the same category as Peltigera, illustrating considerable changes in structure, as does the lamina of Marchantia. In these taxa highly affected by compression the cellular structure is almost completely obliterated and cells become fused to a great extent, which sometimes generates pseudocellular structures. Additionally, stratification produced by compaction is conspicuous. Many of these features are reminiscent of those seen in thalloid fossils from the Early Silurian (Llandovery) Passage Creek biota of Virginia, and highlight experiments simulating fossilization as a promising avenue of investigation for elucidating the nature of eukaryotic early terrestrial colonizers.

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1 - Humboldt State University, Department of Biological Sciences, Arcata, California, 95521, USA


Presentation Type: Poster:Posters for Sections
Session: P
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM
Number: P54001
Abstract ID:1746

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