Abstract Detail


El-Abdallah, Samar [1], Marshall, John [2], Holterhoff, Peter [3], Matsunaga, Kelly [4], Tominello-Remorez, Christopher [5], Tomescu, Alexandru [6].

The archaeopterid forests of western Laurentia: flora of the Upper Devonian (lower Frasnian) Maywood Formation of Wyoming.

Afforestation is central to understanding the Devonian System, and documenting phytogeography and plant diversity across the Devonian is key to understanding the history of forests. Eastern Laurentia was a forest diversity hotspot in the Devonian, yet the vegetation of its western edge – comprised of an arid carbonate platform unfavorable to plant fossil preservation – is largely unknown. The Maywood Formation of Wyoming, until recently assigned a late Givetian age, is one of only three Devonian floras previously recognized in western North America and has not been examined in any detail. Recent assessment of the sedimentary facies, palynofacies, and plant macrofossil taphonomy in the Maywood Formation indicate a lagoon or lake margin environment, disconnected from the open marine realm, and support an early Frasnian age (c. 380 Ma) for this unit. The plant fossil assemblage of the Maywood Formation consists of charcoalified wood, adpressions of axes, foliage and sporangia, and a rich palynomorph content. The charcoalified wood conforms to the Callixylon type of archaeopteridalean progymnosperms. It consists of tracheids with grouped pitting and uniseriate rays of low height. The pits, arranged tightly and alternately, are circular bordered pits with oblique slit-shaped apertures. Axes are heavily fragmented and many display rounded ends indicative of strong taphonomic effects. Associated foliage, rarely preserved, is fan-shaped, long and narrow with dissected tips, and fits the morphology of archaeopterid foliage. Axes of other morphologies are exceedingly rare. Sporangia are small (1-2mm) fusiform, with longitudinal dehiscence, characteristic of progymnosperm sporangia. Microspore and megaspore packets representing the undissociated contents of these sporangia fit the morphology of Archaeopteris spores. Consistent with the macro- and mesofossil content, >90% of the palynomorphs are the Archaeopteris microspore Geminospora lemurata and Archaeopteris megaspores are also abundant. Spermasporites-type seed-megaspores are also present in the assemblage. The plant fossil content of the Maywood Formation fills a gap in the phytogeography of the Late Devonian. The fossil assemblage reflects the presence on the western margin of Laurentia of forests heavily dominated by archaeopterids, with sparse presence of other taxa. The Maywood flora is less diverse than many coeval floras in eastern Laurentia, possibly a reflection of ecophysiological constraints imposed by the arid carbonate platform environment. Among the rare other taxa, we note the (currently unknown) parent plant of Spermasporites, for which the Maywood formation represents a western range extension. These plants formed a vegetation that experienced high wildfire incidence in the vicinity of the Maywood basin.

1 - California State Polytechnic - Humboldt, Department of Biological Sciences, 1 Harpst street, Arcata, CA, 95521, USA
2 - University of Southampton, National Oceanography Centre, School of Ocean and Earth Science, European Way, Southampton, SO14 3ZH
3 - Hess Corporation , 1501 McKinney Street , Houston, TX, 77010, USA
4 - University Of Kansas, Ecology And Evolutionary Biology, 1200 Sunnysive Ave., Lawrence, KS, 66045, United States
5 - Technische Universität München, Arcisstraße 21, München, 80333, Germany
6 - California State Polytechnic University - Humboldt, Department of Biological Sciences, Arcata, California, 95521, USA

fossil wood

Presentation Type: Poster
Number: PPB005
Abstract ID:967
Candidate for Awards:None

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