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Abstract Detail


Paleobotanical Section

Tomescu, Alexandru MF [1], Chisholm-Sims, Danza M. [1], Thran, Andrew E. [1].

Experiments simulating fossilization provide clues to the taxonomic affinities of pre-tracheophytic terrestrial fossils.

Assemblages of thalloid fossils from 450-425 Myr old continental sequences of the Appalachian Basin record early stages in the colonization of land by complex eukaryotes and hold clues to the origin of land plants and other terrestrial lineages. In the Passage Creek biota (Virginia, Early Silurian, ca. 440 Myr), carbon isotope signatures have confirmed the terrestrial nature of fossils, indicating that some were liverworts; the diversity of internal structures of fossils suggests presence of a broader taxonomic spectrum. However, fossil preservation as coalified compressions has altered internal structures, precluding direct assessment of taxonomic affinities. Resolution of the latter requires that (1) detailed description of structural features that differentiate fossil types, and (2) characterization of internal structures generated by simulated fossilization of extant terrestrial organisms (bryophytes, lichens, algae, fungi, cyanobacteria), meet mid-way to allow for direct comparisons between fossils and living organisms. SEM analysis allowed for classification of fossils into five types based on structural differences for which a descriptive terminology was developed. A series of experiments simulating fossilization (pressure and heat up to 200°C, 60 days) showed that different groups of extant organisms maintain individuality in terms of internal structure even when the latter is altered by severe experimental treatments. Experiments generated structures similar to those seen in some of the fossil types described in SEM, in liverworts and lichens. Sub-micron sized structural features observed in some fossils in TEM have counterparts in artificially fossilized charophyceans (Spirogyra). Cross-sectional structures compared in light microscopy reveal similarities between fossils and artificially fossilized liverworts, hornworts, lichens, charophyceans, and basidiocarps. Taken together, these findings confirm the presence of a broad taxonomic spectrum in pre-tracheophytic terrestrial communities, bring us closer to resolving the taxonomic affinities of the different components of those communities, and emphasize the utility of the experimental approach in addressing these questions.


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

Keywords:
embryophyte
Fossil
hornwort
lichen
liverwort
Silurian
Spirogyra
thalloid
charophycean.

Presentation Type: Oral Paper:Papers for BSA Sections
Session: 25
Location: Superior A/Cliff Lodge - Level C
Date: Monday, July 27th, 2009
Time: 1:30 PM
Number: 25001
Abstract ID:362


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