Fossil plants from the BeardmoreGlacier area

T. N. TAYLOR

Department of Botany and Institute of Polar StudiesOhio State University

Columbus, Ohio 43210

E. L. SMOOT

Department of Biology,Hope College

Holland, Michigan 49423

With the exception of isolated pieces of silicified wood, by farmost of the fossil plants from Antarctica are preserved as im-pressions in which cellular details are lacking. The discovery ofsilicified plant remains of Permian and Triassic age from theBeardmore Glacier area has provided a unique opportunity toexamine the detailed cellular structure of these floral compo-nents. The silicified plants from these sites are especially impor-tant because they represent one of the very few deposits of thisage in the world where it is possible to investigate detailedanatomical features of plants. Moreover, the Beardmore plantsprovide an important stratigraphic link with the late Car-boniferous floras which are also preserved as cellular per-mineralizations. A multifaceted research program directed atthe antarctic floras is currently in progress and involves inves-tigations of several different types. Three of these are discussedbriefly below.

Paleobotanists have long speculated on the origin of moderncycads, with the medullosan pteridosperms suggested as theprobable ancestors. One component of this research is con-cerned with cycadophyte stems (Taylor, Smoot, and Delevoryas1983) of Triassic age that are anatomically similar to the stems ofmodern members of the Cycadales (e.g., Zamia, Bowenia). Thestems measure approximately 5.0 centimeters in diameter andinclude well preserved petioles. The vascular system consists ofendarch primary bundles that are associated with radial files ofsecondary tracheids possessing scalariform pits. A well pre-served vascular cambium and some secondary phloem is alsopresent. Although paleobotanists have long speculated thatmodern cycads are related to the late Paleozoic medullosanpteridosperms, this assumption has been generally based onvegetative remains, and some common anatomical features ofmedullosan stems (Worsdell 1901). The discovery of cycadstems in the Triassic of Antarctica provides detailed histologicalinformation to indicate that the anatomical features of the stemsare nearly identical with those of extant representatives of theorder.

Another focus of this paleobotanical program concerns thePermian foliage types Glossopteris and Gangamopteris. The spatu-late leaves of these two genera have been the subject of numer-ous contributions that have emphasized taxonomic details. Todate, paleobotanists have had little success in distinguishingthese two taxa using characters that have been consistentlyreliable over wide geographic regions. In addition, there havebeen few attempts to distinguish ontogenetic features fromthose that are phylogenetic.

The discovery of anatomically preserved leaves of these twogenera on rock surfaces provides an opportunity to correlate themorphology and histology of the leaves. This will enable re-searchers to relate the structurally preserved specimens withthe more abundant, and widely occurring, impression-com-pression specimens. Preliminary investigations of these leavesindicate that the so-called midrib in Glossopteris is constructed ofup to five closely spaced, parallel veins, each surrounded by abundle sheath. This feature has been widely used to distinguishthe two taxa, but may be of little taxonomic importance.

A third component of the research is directed at structurallypreserved fungi that are common in certain plant tissue sys-tems. In living plants it is estimated that more than 90 percent ofall vascular plants are associated with certain mycorrhizal fungi.Endomycorrhizal fungi that are morphologically identical to theextant taxon Glomus have been described in the undergroundorgans of a variety of Carboniferous plants (Wagner and Taylor1982). The presence of similar structurally preserved fungi inthe antarctic material not only extends the stratigraphic range ofthese fungi from the Devonian into the Triassic but alsoprovides the opportunity to correlate the host-fungus rela-tionship through an extended segment of geologic time.

The Beardmore specimens allow for an investigation of theanatomy of several groups of major plants that are currentlyvery poorly understood and for which there is almost no infor-mation about cellular detail. The diversity of the flora fromthese sites is exceptional, and information about the fossils willcontribute not only to details about the biology of the organismsbut will also provide a much needed framework with whichimportant evolutionary questions can now be considered.

This research was supported by National Science Foundationgrant DPP 82-13749.

References

Taylor, IN., E.L. Smoot, and T. Delevoryas. 1983. Structurally pre-served plants from Antarctica: A Triassic cycad stem. American Journalof Botany, 70, 80.

Wagner, C.A., and TN. Taylor. 1982. Fungal chlamydospores from thePennsylvanian of North America. Review of Palaeobotany and Pal-ynology, 37, 317-328.

Worsdell, W.C. 1901. Contributions to the comparative anatomy of theCycadaceae. Transactions of the Linnean Society, 2nd Series, Botany, 6,109-121.

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