Hermsen, E. J. , Taylor, Thomas N. , Taylor, Edith L. , Stevenson, Dennis Wm. .
The Triassic cycad Antarcticycas: an early representative in the age of cycads.
UNTIL recently, Antarcticycas (structurally preserved stems and roots), and Delemaya (microstrobilus with pollen), represented the only cycad remains described from the Middle Triassic Fremouw Formation, Antarctica. Cataphylls associated with Antarcticycas stems and detached cycad petioles have now been identified from the same deposits. The cataphylls of Antarcticycas are roughly triangular in transverse section with an inverted omega-shaped pattern of petiole vascular bundles; like cataphylls of extant cycads, they have vascular bundles lacking fascicular cambia and are associated with straight traces. The unnamed petioles are clearly cycadalean; they have the characteristic inverted omega-shaped pattern of vascular bundles that is a synapomorphy for Cycadales. As in petioles of extant genera, they have well-developed vascular bundles that are interpreted as having fascicular cambia. Although not found in attachment, we hypothesize that these organs represent part of the same parent plant because they co-occur in the Fremouw flora to the exclusion of other cycad remains. Using extant cycads thought to be of similar growth form as models, we have reconstructed the Antarcticycas plant. This plant is small, possibly subterranean, lacks persistent leaf bases, and has dichotomous branching; the relative arrangement of leaves, cataphylls, and strobili is currently conjectural. Despite this, the Antarcticycas plant is among the most thoroughly documented fossil cycad reconstructions, similar in the number of organs known from the fossil record to Leptocycas (Triassic) and the Androstrobus-Beania-Nilssonia plant (Jurassic).[c.e.:srb]
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1 - University of Kansas, Ecology and Evolutionary Biology, Haworth Hall, 1200 Sunnyside Avenue, Lawrence, Kansas, 66045-7534, USA
2 - University of Kansas, Department of Ecology & Evolutionary Biology, Natural History Museum and Biodiversity Research Center, 1200 Sunnyside Avenue, Lawrence, Kansas, 66045-7534, USA
3 - New York Botanical Garden, Institute of Systematic Botany, 200Th Street & Southern Boulevard, Bronx, New York, 10458-5126, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Tuesday, August 1st, 2006
Time: 8:45 AM