Shackleton Glacier Area: Evolution of Vegetation during the Triassic

University Of Kansas Center For Research Inc, Lawrence KS

Investigators

Abstract

This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports a study of the Triassic plant fossils from the Central Transantarctic Mountains. The terrestrial rocks of the central Transantarctic Mountains have been a source of outstanding fossil discoveries over the last 30 years, including Permian and Triassic permineralized peat, fossil forests silicified in growth position, and compression floras with cuticular preservation, as well as the interesting Sirius Group fossils, and the first Jurassic dinosaur from the continent, to name only a few. The rare juxtaposition of sites that include many different types of plant preservation, the exceptional quality of the plant fossils, and the biodiversity of the sites make this area unique in the world. The Paleozoic/Mesozoic transition is a critical time in plant evolution. A unique variety of seed plant groups existed and several of these have been suggested as angiosperm (flowering plant) ancestors. There was also a massive floral change from the Permian to the Triassic. The Permian of Gondwana is dominated by glossopterid seed ferns (leaf type = Glossopteris), but these plants disappeared at the boundary to be replaced by the corystosperm seed ferns (leaf type = Dicroidium), which persisted throughout the Triassic. Although the Corystospermales were the dominant plant group in the Triassic of Gondwana, we currently know very little about their biology and evolution. Recent additions to our knowledge of corystosperm phylogeny have come from permineralized peat from the Beardmore Glacier area and from exceptionally well-preserved compression fossils from the Shackleton Glacier area. While most fossil plants occur as disarticulates leaves, stems, and reproductive organs, many in the Shackleton Glacier area are partially articulated, thus making it possible to relate the diversity of plant parts and gain a more accurate picture of the entire plant and its place within the ecosystem. This project will center on the collection and study of Triassic floras from the Shackleton Glacier area. Fieldwork will be conducted in the 2003-2004 field season using two remote camps established via Twin Otter of helicopter. The sites to be collected include Collinson Ridge and an unnamed ridge southeast of Schroeder Hill. The latter has already yielded the only known example of a Dicroidium frond organically attached to an axis bearing Umkomasia reproductive organs, which has allowed a better understanding of the phylogenetic position of these enigmatic seed plants, especially in relationship to flowering plants. In addition to compression fossils, this site also includes some permineralized peat and in situ fossil stumps. The Collinson Ridge site is important because it contains fossil peat and logs in presumably Lower Triassic rocks. Megafossil plants of this age are currently unknown on the continent, although palynomorphs have been recovered and root traces are relatively common. Preliminary analysis of petrified material collected during the 1995-1996 field season, however, shows a large number of Glossopteris leaves in this peat, suggesting that perhaps it is Late Permian rather than Early Triassic. Thus the fossil flora, as it is currently known, is at odds with the age based on vertebrate fossils. It is important to elucidate the biostratigraphy of this area because the position of the Permian-Triassic boundary is crucial in understanding the timing of terrestrial extinctions around the boundary. Further collecting at both of these sites and analysis of the fossil material in the laboratory will address these discrepancies and yield important new information about Triassic plant evolution. Paleobotany is ideally suited to education and outreach activities. Workshops and temporary exhibits have been developed on Antarctic science through the public outreach programs of the University of Kansas Natural History Museum and Biodiversity Research Center, and this activity will be continued under this project. Student involvement has also been extensive and will be continued through research experiences for undergraduates.