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A Late Triassic Flora from the Allan Hills, Southern Victoria Land

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A Late Triassic Flora from the Allan Hills, Southern Victoria Land A Late Triassic flora AF from the Allan Hills, southern Victoria Land EDITH L. TAYLOR, THOMAS N. TAYLOR, BRIGITTE MEYER-BERTHAUD, and JOHN L. ISBELL Department of Plant Biology and Byrd Polar Research Center 4 , Ohio State University 4 I 4 Columbus, Ohio 43210 N. RUBEN CUNEO Museo Argentino de Ciencias Naturales "B. Rivadavia" Buenos Aires, Argentina Figure 1. Flattened cupule of a seed tern. (Bar scale = 1 centimeter.) In this article, we describe the occurrence of a well-preserved Late Triassic flora from the Allan Hills, southern Victoria Land. The plants are preserved as impression/compressions in gray, fine-grained siltstones that outcrop along the western side of ternodal distances ranging from 2.0 to 3.0 millimeters. Each the eastern arm of the Allan Hills. In some instances, cuticles leaf is 3.0 to 4.0 millimeters long and approximately 1.0 mil- are present. Collections were made from three different ho- limeter wide. A single ginkgophyte leaf was also found at this rizons during the 1989-1990 austral summer. The two upper level. Reproductive organs include numerous, isolated seeds, horizons are within Member C of the Lashly Formation and one cone about 3.0 centimeters long and two other slightly the third collection comes from siltstone lenses on a sandstone larger cones with scales of the Rissikia type (Townrow 1967b). platform within Member B of the Lashly. Plant level 2. The plants occur in a siltstone lens approxi- Plant level 1. The largest collection of megafossils occurs at mately 2 meters below level 1, with the most common element this level in a unit that varies from approximately 20 centi- being Dicroidium cf. dutoitii. Cupules are also present, together meters to 1.0 meter in thickness. One of the most common with clusters of pollen sacs similar to Pteruchus or Antevsia. elements of the flora is an osmundaceous fern, in particular specimens that include both vegetative and reproductive parts. Also present are several species of the seed fern Dicroidium. One species, D. cf dutoitii, is often associated with large, stalked cupule-like structures. Each flattened cupule measures ap- proximately 1.0 centimeter in diameter and is attached to a slender stalk. The specimen illustrated in figure 1 is com- pressed from the stalk side and shows the region of stalk attachment. In none of the specimens has it been possible to identify whether the cupules are uni- or multiovulate, although on some specimens the surface is irregular, suggesting that there were several ovules produced by each cupule. Associated with the cupules are clusters of elongate pollen sacs with in- dividual sporangia that measure approximately 2.0 millimeters long. Also included in the flora from level 1 are several foliage types. One of these is similar to cf. "Johnstonia" trilobita, which was previously described by Townrow (1967a) from the Allan - Hills. Our preliminary observations suggest that the pinnules in the present material are similar in size but possess a more acute distal tip. Another possible seed fern foliage type that is relatively common at this level-is Diplasiophyllum acutum. Also present are long (8.5 centimeter) strap-shaped leaves with parallel veins, which morphologically resemble leaves of the Desmiophyllum or Heidiphyllum type (figure 2). They also share some similarities with leaves described by Plumstead (1962) 1Z from southern Victoria Land as Zamites, and from Livingston Island as Sphaenobaiera (Banerji and Lemoigne 1987). The level I flora also includes a leafy axis (figure 3) similar to Phyllotheca Figure 2. Desmiophyllum leaf showing parallel venation. (Bar scale (Townrow 1955). The leaves are attached along an axis at in- = 1 centimeter.) 20 ANTARCTIC JOURNAL • A very high percentage of the plants at all three levels con- tain some cuticular remains. The presence of cuticle on plant parts from Antarctica is relatively rare; when present, it pro- vides an important set of diagnostic features that can be used along with morphology to establish the relationships among disarticulated plant organs. In addition to the impression/compression floral elements, the sandstone platform in Member B (level 3) also contains scattered peat rafts containing silicified plants (Gabites 1985). Numerous silicified trunks are also present on the platform, some up to 8.0 meters long. In many of the trunks, it is possible to see well-developed growth rings in the wood. Triassic sil- icified plants have also been reported from Fremouw Peak (Beardmore Glacier area) and have provided a great deal of information about the plants from this period (Taylor and Tay- lor 1989). The peat at the Allan Hills locality is more compacted J and degraded than that from Fremouw Peak, but plant organs are still recognizable. The presence of plants preserved as both impression/compressions and as silicified permineralizations at the same locality affords the rare opportunity to study not only the morphology but also the anatomy of a particular plant organ. The impression/compression data can be used in bios- tratigraphic and biogeographic correlations, while information obtained from the silicified plants can be used in a more biol- ogic and evolutionary context. This work was supported in part by National Science Foun- dation grants DPP 86-11884 and DPP 88-15976. We are espe- cially appreciative of the logistic support provided by the U.S. Navy VXE-6 Squadron. Figure 3. Portion of a sphenophyte shoot. (Bar scale = 1 centi- meter.) Leaves of the Desmiophyllum type are abundant at this level. Several coniferous shoots, some containing short shoots, are also common. These resemble vegetative conifer remains in- References cluded in the genus Brachyphyllum. Plant level 3. A few plant fossils were also found in siltstone Banerji, J., and Y. Lemoigne. 1987. Significant additions to the Upper lenses in Member B of the Lashly Formation. These include Triassic flora of Williams Point, Livingston Island, South Shetlands Dicroidium odontopteroides and fragments of several fern pinnae. (Antarctica). Géobios, 20, 469-487. Gabites, H.I. 1985. Triassic Paleoecology of the Lashly Formation, The plant fossils from the Allan Hills site are of special in- terest for several reasons: Transantarctic Mountains, Antarctica. (Unpublished M.S. Thesis, Victoria University of Wellington.) • Each of the levels examined appears to contain different Plumstead, E.P. 1962. Fossil floras of Antarctica. In Trans-Antarctic plant assemblages. Pteridophytes are the most common ele- Expedition, 1955-1958, (Science Report 9, Geology). London: Trans- ment in level 1, with osmundaceous ferns the principal com- antarctic Expedition Committee. ponent of the flora. At level 2, ferns are absent and seed Taylor, T.N., and E.L. Taylor. 1989. Bibliography of Antarctic paleo- ferns are the most common flora element. This level also botany and palynology. In T.N. Taylor and E.L. Taylor (Eds.), Ant- contains conifers, but forms that are different from those arctic paleobiology—its role in the reconstruction of Gondwana. New York: encountered in level 1. Although plant remains are rare in Springer-Verlag. level 3, they are different from those encountered at either Townrow, J.A. 1955. On some species of Phyllotheca. Journal and Pro- level I or 2. ceedings of the Royal Society of New South Wales, 89, 39-63. • Levels 1 and 2 contain both vegetative and reproductive Townrow, J.A. 1967a. Fossils plants from the Allan and Carapace Nunataks, and from the Upper Mill and Shackleton Glaciers, Ant- remains. This greatly increases the opportunity to demon - arctica. New Zealand Journal of Geology and Geophysics, 10, strate a relationship between fertile and sterile organs of the 456-473. Townrow, J.A. 1967b. On Rissikia and Mataia podocarpaceous conifers same plant, and thus makes it possible to reconstruct the from the Lower Mesozoic of Southern Lands. Papers and Proceedings entire organism. of the Royal Society of Tasmania, 101, 103-136. 1990 REVIEW 21.
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