Tomescu, Alexandru MF , Steenbock, Christopher M. , Caruso, Joseph A. .
Environments of the Early Devonian Beartooth Butte Formation floras (Wyoming) and the evolution of rooting systems.
New collections from the two fossiliferous localities of the Early Devonian (Pragian-Emsian, 400-410 Myr old) Beartooth Butte Formation (Wyoming) are refining our image of depositional environments of the plant assemblages. At the Beartooth Butte locality, scattered and fragmentary fossils likely reflect incidental transport and preservation of plants in marine deposits. In this context, the affinities of Sphondylophyton, a taxon characterized by whorled appendages, probably lie within the algal realm, rather than among the sphenopsids. Problematic access to the fossil layers makes detailed evaluation of depositional environments at this locality difficult. At the Cottonwood Canyon locality, stratigraphic excavation produced new evidence for locally variable depositional environments within small (10-50 cm) vertical distances, and including terrestrial episodes: levels containing highly fragmented plant material mixed with fish and eurypterid remains alternate with horizons reflecting in situ preservation of plant fossils. The latter include several horizons with horizontal and vertical rooting structures, a layer with densely packed Drepanophycus stems, and plant axes forming large tufts. The unequivocal evidence for autochthonous fossil plant assemblages adds resolution to previous interpretations which characterized the Cottonwood Canyon assemblages only generally, as tidal/fluvial. These assemblages represent environments that straddled the water-land interface and witnessed high frequency changes in sedimentation which alternated episodes of vegetation establishment, with high energy, flooding phases. This information is important in constraining the ecology of the fish, eurypterids, and microconchids co-occurring in the plant assemblages. Microconchids, solitary lophophorates that colonize diverse substrates with their minute calcified tubes, are ubiquitous on plants in the Beartooth Butte Formation, and sometimes highly abundant, attesting to extended waterlogging of the vegetal material prior to burial. Aside from taphonomic information, the new collections from Cottonwood Canyon contain the first unequivocal trimerophyte sporangia in the Beartooth Butte Formation, as well as additional specimens of minute rosette-shaped compressions representing putative land plant gametophytes, and add to the body of knowledge on early land plant rooting systems.
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1 - Humboldt State University, Department of Biological Sciences, Arcata, California, 95521, USA
2 - Humboldt State University, Department of Biological Sciences, Arcata, CA, 95521, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 555B/Convention Center
Date: Monday, August 2nd, 2010
Time: 1:30 PM