TRIASSIC FLORAS OF ANTARCTICA: PALEOBIOLOGY AND PALEOECOLOGY OF POLAR LATITUDE COMMUNITIES

We present a synthesis of research conducted during the last 20 years on fossils collected in Middle–Late Triassic formations of the Beardmore Glacier area, Central Transantarctic Mountains, Antarctica. The presence of both compressed/impressed and permineralized specimens allows the detailed description of individual organs (e.g., leaves, seeds, roots, etc.) as well as the reconstruction of a whole organism concept for several Antarctic taxa. This last concept represents an essential tool for a deeper understanding of the paleobiology of high-latitude plants, the paleoecology of the ecosystems, and the phylogenetic relationships of Triassic plants.

In general terms, the highly diverse floras include lycopsids, sphenopsids, ferns, and gymnosperms. The ferns are particularly diverse, including the families Gleicheniaceae, Matoniaceae, Osmundaceae, Marattiaceae, Cyatheaceae (?), and other enigmatic forms. The gymnosperms also show an interesting diversity and are represented by cycads, seed ferns, and conifers. Recent data show the presence of ginkgoaleans, a group previously unknown in early Mesozoic Antarctic communities, a new type of enigmatic ovule, and a voltzian pollen cone with in situ pollen. In addition, anatomically preserved material, including trunks, leaves, roots, and pollen cones, has provided one of the most complete reconstructions of a fossil cycad in the world. The possibility of reconstructing complete organisms represents a considerable advancement in the resolution of evolutionary relationships in Triassic plants, and provides important data on the adaptations of these plants to polar latitudes.

Anatomically preserved specimens found in permineralized peat provide exceptional data on the ecology of these plants, including their interactions with microorganisms and arthropods, and ephemeral stages of the life history of some of the seed plants, such as embryo development. These remarkably well-preserved and diverse taphofloras, including well-preserved fossil tree rings, provide a unique opportunity to understand the functioning of ecosystems in a strongly seasonal, high-latitude environment that has no modern equivalent.