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Abstract Detail


Bippus, Alexander [1], Tomescu, Alexandru [2].

Characterizing the Early Devonian plant communities of western North America: the Lochkovian-Pragian Cottonwood Canyon flora of Wyoming .

The Cottonwood Canyon flora consists of Lochkovian-Pragian (419-410 Ma) fossil assemblages preserved in rocks assigned to the Beartooth Butte Formation, in northern Wyoming. Although >90 Lochkovian and Pragian plant fossil assemblages are known worldwide, the Cottonwood Canyon flora is the only Early Devonian flora of significance known in Western North America; two other Devonian floras in this geographic region (Martin Formation of Arizona and Chilliwack Group of Washington) are poorly sampled and probably younger. The Early Devonian witnessed the first stages of the evolutionary radiation of tracheophytes, during which several lineages of structurally-simple vascular plants diversified to generate the different types of structurally-complex tracheophytes described from younger, Middle Devonian floras. Understanding Early Devonian plant diversity is, thus, essential for untangling the evolution and relationships of early tracheophytes. The Cottonwood Canyon flora has been sampled since the 1970s and collections are housed at several major museums in the United States. However, despite its geographic significance and extensive sampling, the Cottonwood Canyon flora has not received a modern formal taxonomic treatment. Plants are preserved in abundance at Cottonwood Canyon, as coalified compressions or impressions. A survey of all the material collected from this flora reveals plants with diverse taxonomic affinities, including three zosterophylls, a renalioid, three lycophytes, two trimerophytes, and thalloid gametophytes of riccioid appearance; specimens potentially representing four additional morphotypes have been recorded. The two most abundant plants are Sengelia radicans, a drepanophycalean lycophyte identified in 52% of the samples, and a zosterophyll (present in 24% of samples) represented by axes that branch at wide angles with subaxillary tubercles and stalked globose sporangia; both of these are found predominantly in monospecific autochthonous and parautochthonous layers. Sporangia are rare on the Cottonwood Canyon plants and especially rare in the in situ/parautochthonous assemblages. This paucity of reproductive structures, very striking considering the large number of vegetative remains, points to clonality as the prevailing reproductive strategy, especially for the abundant zosterphyll and Sengelia. Clonality has been noted previously in other Early Devonian plant assemblages, e.g., the Battery Point Formation of Gaspé (Canada). While the relatively high level of plant diversity documented at Cottonwood Canyon is not unusual for Lochovian-Pragian localities, this flora is the only source of information on the vegetation of western North America during the Early Devonian, thus contributing significantly to the picture of Early Devonian plant diversity and biogeography.

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1 - Humboldt State University, Department of Biological Sciences, 1 Harpst Street, Arcata, CA, 95521, United States
2 - Humboldt State University, Department Of Biological Sciences, 1 Harpst Street, Arcata, CA, 95521, USA

Early Devonian

Presentation Type: Oral Paper
Session: 12, Cookson/Moseley award presentations
Location: Sundance 4/Omni Hotel
Date: Monday, June 26th, 2017
Time: 3:00 PM
Number: 12007
Abstract ID:118
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award

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