Decombeix, Anne-Laure , Taylor, Edith , Taylor, Thomas .
Anatomy and affinities of permineralized corystosperm trunks from the Middle Triassic of Antarctica: new data and synthesis.
Anatomically preserved stems of Middle Triassic corystosperm seed ferns from the Central Transantarctic Mountains include (1) trunks of Jeffersonioxylon from Gordon Valley found in association with Dicroidium leaf compressions and (2) young stems of Kykloxylon from Fremouw Peak bearing Dicroidium leaf bases. Neither taxon is comparable to the corystosperm trunk morphogenus Rhexoxylon, and it has been suggested that the habit of the Antarctic corystosperms differed from the tree-fern like reconstruction based on the association of Rhexoxylon and Dicroidium in the Triassic of South America. We have previously hypothesized, based on portions of trunks with preserved bark from Fremouw Peak, that stems with a Rhexoxylon-like dissected xylem cylinder actually correspond to the outer part of fluted trunk bases.
New specimens from Fremouw Peak, including material collected during the 2010-2011 austral field season, support this concept. Permineralized trunks 50 cm or more in diameter are preserved in fluvial sandstone channels at the locality. The base of the trees is often surrounded by silicified peat and is the only region where the bark is preserved. The secondary xylem is locally highly lobed, with included bark tissues, and isolated fragments somewhat resemble the outer part of a Rhexoxylon axis. The decorticated, more distal part of the trees shows a fluted secondary xylem cylinder. The central part of the trunks, as well as branches also found in the enclosing sandstone, however, lack evidence of the complex vascular system typical of Rhexoxylon. The simple stelar anatomy is indeed more comparable to that of young stems of Kykloxylon known from the permineralized peat at the same site. The similarities of the Antarctic specimens with South American corystosperm trunks with a so-called normal cylinder axis, such as Cuneumxylon and Tranquiloxylon, will be discussed.
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1 - University Of Kansas, 1200 Sunnyside Ave., Haworth Hall, Lawrence, KS, 66045-7534, USA
2 - University Of Kansas, Department Of Ecology And Evolutionary Biology, 1200 Sunnyside Avenue, Haworth Hall, Lawrence, KS, 66045-7600, USA
3 - University Of Kansas, Department Of Ecology And Evolutionary Biology, 1200 Sunnyside Avenue, Haworth Hall, Lawrence, KS, 66045-2106, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Forsyth Room/Chase Park Plaza
Date: Wednesday, July 13th, 2011
Time: 8:15 AM