Axsmith, Brian , Upchurch, Garland , Jacobs, Bonnie .
New Pseudofrenopsis varians (Cheirolepidiaceae) Fossils from the Cretaceous of Texas and Arkansas: Structural and Paleoecological Implications.
REMAINS of the cheirolepidiaceous conifer Pseudofrenelopsis varians are common in marine carbonates of the Lower Cretaceous Trinity Group. In addition to being the type species of a widespread fossil conifer genus, P. varians provides the most convincing example of an obligate halophyte among conifers, and has been reconstructed as a small stem-succulent similar to the modern angiosperm Salicornia. Newly examined remains of P. varians from the Barker Branch locality of the Glen Rose Formation of Texas provide additional evidence for a halophyte ecology, but suggest that the species represented a large shrub or small tree. A monospecific assemblage of P. varians shoots with well-preserved cuticles occurs in association with woody axes up to 1.3 cm in diameter. Some cuticle-bearing shoots are encrusted with serpulid worm tubes and other marine invertebrates, suggesting that portions of the plant were submerged or regularly inundated with salt water. Associated woody axes have two layers of carbonized tissue; the inner has tracheid-like structures suggestive of pycnoxylic wood, while the outer has an irregular fracture pattern suggestive of periderm. Height estimates derived from these axes indicate that P. varians was 1-2 m tall, while estimates derived from larger woody axes reported from the same locality indicate that P. varians may have been at least 2.5 m tall. We also report a new occurrence of P. varians shoots from a quarry in Howard County Arkansas that produces abundant P. parceramosa remains. Within the quarry, P. varians occurs with marine invertebrates of the Dirks Limestone Member of the Cossatot Formation, while P. parceramosa occurs only in clastic sediments of the conformably overlying Holly Creek Formation. This mutually exclusive facies distribution at a single locality provides strong support for the classic paleoecological interpretation of P. varians as an obligate halophyte and P. parceramosa as a facultative halophyte or non-halophyte.
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1 - University of South Alabama, Biological Sciences, Life Sciences Bldg. #124, 307 University Blvd. North, Mobile, Alabama, 36688, USA
2 - Texas State University, Department of Biology, 601 University Drive, San Marcos, Texas, 78666, USA
3 - Southern Methodist University, Environmental Science Progrm, P.O. Box 750395, Dallas, Texas, 75275, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Tuesday, August 1st, 2006
Time: 9:30 AM