Abstract Detail

Paleobotanical Section

Graham, Linda [1], Cardona-Correa, Christopher [2], Kodner, Robin [3].

Ordovician fossil evidence for Sphagnum moss.

Modern Sphagnum-dominated peatlands store a very large proportion of global soil carbon as peat, such long-term sequestration fostering global climate homeostasis. Peatlands also harbor distinctive species, including microbial associates such as methanotrophs and nitrogen fixers that play globally important roles in Earth’s biogeochemical cycles. Although fossils attributed to Sphagnum-like peatmosses are known from the Permian (Neuberg, 1956, 1960), recent molecular clock analyses suggest that peatmosses might well be considerably older. Because certain Caradocian microfossils had been interpreted by Kroken et al. (1996, AJB 83:1241) as the resistant remains of sporophytic capsule epidermis of Sphagnum-like early mosses, we examined well-understood shallow marine mid-Ordovician dolomites (Sinnipee Group), located in Dane Co., WI, and dated at 455-460 Mya, for evidence of peatmosses. Here we report that in two collections made 12 years apart, using methods designed to avoid contamination with modern materials, we found previously undescribed organic microfossil remains closely resembling portions of leaves and stems of modern Sphagnum. Morphometric analyses indicate that the two sets of samples likely represent the same peatmoss species, although the remains were too fragmentary to link with any modern peatmoss species. The fossil fragments display the same types of cell wall autofluorescence previously described for dead or acetolyzed modern peatmosses (Kroken et al. 1996), suggesting that phenolic cell wall polymers were likewise present in ancient relatives and resisted microbial hydrolysis long enough to achieve sedimentary burial even under suboptimal preservational circumstances. No traces of chlorophyll fluorescence were observed and mineral particles occurred within hyaline and putative chlorophyllous cells, indicating exposure to and intrusion into cell lumens by external sediments. The mid-Ordovician peatmoss microfossils were isolated from a location near a site from which we had earlier reported the oldest known fossil glomalean fungi, their presence suggesting a vegetated terrestrial source (Redeker, Kodner & Graham 2000, Science 289:1920). The new remains resembling modern Sphagnum add to accumulating evidence that early bryophytes were important components of Ordovician landscapes. The Sphagnum-like microfossils also indicate that peatlands similar in biogeochemical function to those of modern times have existed since the mid-Ordovician, a much longer time period than previously thought. These new fossils open an exciting window into Earth’s first peatlands and should also be useful in calibrating molecular clocks.

Broader Impacts:

1 - University of Wisconsin, Botany Dept, 211 Birge Hall, 430 Lincoln Drive, Madison, WI, 53706, USA
2 - University of Wisconsin-Madison, Botany, 430 Lincoln Drive, Madison, WI, 53706, USA
3 - Western Washington University, Biology, Mail Stop 9160, Bellingham, WA, 98225, USA

Keywords:
Ordovician
Sphagnum.

Presentation Type: Oral Paper:Papers for Sections
Session: 12
Location: Melrose/Riverside Hilton
Date: Monday, July 29th, 2013
Time: 1:45 PM
Number: 12002
Abstract ID:169
Candidate for Awards:None