Dunn, Michael T .
A new pycnoxylic lyginopterid from the Fayetteville Formation (Late Mississippian) of Arkansas.
The Lyginopteridaceae are a diverse group of seed ferns that are commonly thought to include 10 manoxylic genera, and a group of problematic pycnoxylic taxa. These problematic taxa include Protopitys, Pitys, Eristophyton, Bilignea, Stanwoodia, Endoxylon and Megaloxylon and range from the lower to upper Mississippian of Europe and North America. Four new specimens from the Fayetteville Formation of Arkansas represent a new stem morphotaxon and are tentatively placed within this group. The Fayetteville Formation is primarily a marine black shale unit from which an abundant and diverse assemblage of marine invertebrates as well as polynomorphs date the new specimens as middle Chesterian/ uppermost Mississippian in age. The four new stems are all decorticated and the largest and best preserved is 143 cm long and almost 5 cm in diameter. The specimens produce a broad parenchymatous pith with a eustele that consists of numerous anastomosing sympodia that form a net-like cylinder. Leaf traces diverge in a helical pattern, originating from several sympodia, with relatively short internodes. The traces are approximately 2mm in diameter and do not occlude. Secondary xylem consists of narrow tracheids forming dense wood with narrow rays. Preserved wood is up to 12 mm thick and no annual growth rings have been observed. Tracheid pitting is reticulate to multiseriate. The dense wood suggests these were upright plants but branching architecture has not been observed.
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1 - Cameron University, Department of Biological Sciences, Science Complex, Lawton, Oklahoma, 73505, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Williford A/Hilton
Date: Monday, July 9th, 2007
Time: 2:30 PM