Chaney, Dan S. , DiMichele, William A. , Mamay, Sergius H. .
A New Peltasperm with affinities to Comia from the Lower Permian of north central Texas:.
A new genus of probable peltaspermous affinity, similar to the genus Comia Zalessky has been found in rocks of Lower Permian age from north central Texas. Foliar material of this plant has been collected over 15 years but the growth habit is unknown. The leaf is a once pinnate frond characterized by overtopping with increase in pinnule size acropetally, terminated by two large, ultimate and penultimate pinnules. Venation is distinctly comioid, consisting of three orders, the ultimate veins organized either into fascicles or arising singly directly from the pinnule midvein. The new form can be distinguished from Comiaby the presence of ultimate-vein blind endings and by anastomoses among the ultimate veins both within fascicles and between fascicular and isolated veins. Consequently, some ultimate veins to not reach the pinnule margin. In Comiaanastomoses and blind endings are unreported and all ultimate veins reach the pinnule margin. Anatomical features have been preserved by iron mineralization. The epidermis is uniseriate. Stomata occur on the adaxial surface, but the leaf probably is amphistomatic. Laminar stomata are round, approximately 52 μm in diameter, randomly oriented and distributed. There are approximately 15,000 / cm2. Palisade mesophyll is approximately 0.02 cm thick. Specimens occur in channel-form deposits, representing ponds and streams, suggesting growth along stream margins. Associated paleosols and Carbon isotopic analyses indicate seasonal moisture availability and warm temperatures. This morphotype is similar to foliage reported from the Middle Permian of Oman. The Oman form has overtopping and similar venation but is not known to exhibit the ultimate vein anastomoses or blind endings found in the Texas material. The earlier occurrence of this plant in the western equatorial Pangea prior to its occurrence later in western equatorial and higher latitudes replicates a pattern found in several other prominent Permian taxa.
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1 - NMNH Smithsonian Institution, Department of Paleobiology, MRC-121, Washington, DC, 20560, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 31st, 2006
Time: 11:00 AM