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(American Journal of Botany. 2002;89:1004-1013.)
© 2002 Botanical Society of America, Inc.

Paleobotany

Morphologically complex plant macrofossils from the Late Silurian of Arctic Canada1

Michele E. Kotyk5, James F. Basinger, Patricia G. Gensel6 and Tim A. de Freitas

Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E2, Canada; Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3280, USA; Nexen Inc., 2900, 240-4th Ave. SW, Calgary, Alberta, T2P 5C1, Canada

In addition to vegetative remains, fertile remains from ten plants, representing seven distinct taxa whose size and complexity are much greater than most contemporaneous fossils, are reported from late Ludlow (Ludfordian) sediments of Bathurst Island in Nunavut, Canada. Evidence for the age of these beds is gathered from stratigraphic relationships and index fossils including conodonts, graptolites, and brachiopods. Zosterophylls dominate the collection, some of which constitute the earliest record of fertile structures arranged in dense clusters and longitudinal rows along axes. Representatives include a plant that resembles Bathurstia, one species of Zosterophyllum, and two specimens that bear affinity to this genus. Distichophytum is also represented, as is a new zosterophyll named Macivera gracilis. The prevalence of sporangial clustering and reduced sporangial stalks in this flora leads to a discussion of the origins and significance of these morphological features. Following a review of some of the other Silurian floras, particularly the Baragwanathia-bearing Lower Plant Assemblage of Victoria, Australia, which also shows morphological advancement over the rhyniophytoid-dominated floras common to Laurussia, it is concluded that the Bathurst Island flora presents the best evidence to date of substantial morphological diversity, complexity, and stature of vascular land plants in this period.

Key Words: Arctic • Bathurst Island, Canada • evolution • fossil • paleobotany • plant • Silurian






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