Decombeix, Anne-Laure , Taylor, Edith L. , Taylor, Thomas N. .
A permineralized gymnosperm trunk with preserved cortex from the Middle Triassic of Antarctica: anatomy and affinities.
Middle Triassic axes with extensive pycnoxylic wood from Antarctica correspond to podocarp conifers and corystosperm seed ferns. Young stems with attached leaf bases are known for both groups. Larger specimens, including decorticated Jeffersonioxylon stumps and a portion of an axis with Rhexoxylon-like anatomy, have also been described for the corystosperms. In this presentation we describe a permineralized trunk with preserved cortex from the Fremouw Formation. The pith is absent, but the preserved portion of the vascular cylinder has a maximum thickness of 11 cm. The secondary xylem is composed of tracheids with 1-2 rows of circular bordered pits on their radial walls and uniseriate parenchymatous rays. Approximately 30 distinct growth rings each with a very small amount of latewood can be identified in the inner 7 cm of secondary xylem. In the outer part, rings have a faint boundary and are more irregular. The cortex is up to 1.8 cm wide and composed of a parenchymatous ground tissue containing scattered cells with opaque contents and clusters of thick-walled cells. This tissue also contains numerous fan-shaped vascular bundles with secondary xylem and phloem. The outer part of the trunk consists of a thin periderm with a very irregular outline, sometimes folding back on itself. 'Traces' up to 3.5 x 0.4 cm are present in the woody cylinder. Trace anatomy is similar to that of the cortex and each contains several vascular bundles. The nature of these traces (wounds or traces to lateral organs) is discussed. The affinities of the trunk are also considered based on a comparison with the podocarp and corystosperm axes from the Fremouw Formation, as well as with other contemporaneous taxa from Gondwana.
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1 - University of Kansas, Department of Ecology & Evolutionary Biology, Natural History Museum and Biodiversity Research Center, 1200 Sunnyside Avenue, Lawrence, Kansas, 66045-7534, USA
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Superior A/Cliff Lodge - Level C
Date: Wednesday, July 29th, 2009
Time: 8:00 AM