Triassic Kykloxylon wood (Umkomasiaceae, Gymnospermopsida) from Skinner Ridge, northern Victoria Land, East Antarctica

Abstract

During the first Korea Antarctic Geological Expedition (KAGEX I, 2013/2014), fossil wood was collected from the Triassic fluvial deposits of the Beacon Supergroup at Skinner Ridge in northern Victoria Land, Antarctica. The material is coalified and partially silicified; most specimens are slightly compressed due to burial compaction. In spite of this imperfect preservation, anatomical features of both the xylem and the pith could be observed in some specimens. The xylem displays prominent growth rings and usually araucarioid or somewhat mixed-type radial pitting with some abnormal rings partly composed of parenchymatous tissues. Some specimens also have a wood cylinder that is divided radially by parenchymatous zones. These anatomical features indicate a systematic affinity with Kykloxylon Mey.-Berth., T.N.Taylor et Ed.L.Taylor, a characteristic wood type of the Umkomaciaceae, which flourished throughout Gondwana during the Triassic. The Kykloxylon specimens in this study represent the only wood fossil taxon in the Triassic of Victoria Land, except for a dubious report of Antarcticoxylon Seward in 1914. This may indicate a low diversity of Triassic wood fossils in this area, as in other parts of Antarctica. On the contrary, diverse other gymnosperm organs are known to occur in the Triassic of Antarctica. This low diversity of wood taxa compared to the various plant organs in the Triassic of Antarctica is remarkable. We hypothesize three major reasons for this: 1) the overall structural uniformity of gymnosperm wood compared to other vegetative and especially reproductive organ diversity; 2) the overwhelming dominance of corystosperm plants, with a minor component of voltzialean conifers in the canopy-forming forest vegetation during the Triassic in Antarctica; and 3) the very few systematic studies of fossil wood compared to other plant macrofossils.