A SEED PROFILE FROM THE EARLY PERMIAN RED BEDS OF TEXAS

Seeds represent one of the most ecologically informative attributes of terrestrial plants. Strongly tied to dispersal and to the survival of the next generation, seed morphology reveals the dynamics of early Permian plant communities. We analyzed the seeds preserved in the strata of the Clear Fork Group of North-Central Texas (Leonardian/Kasimovian). Consisting of continental, fine grained red mudrocks with interbedded sandstones, the formation is heavily over-printed by pedogenesis, with fossiliferous deposits occurring primarily in small lake or pond deposits. Our study is based on 149 collections from the region, housed in the National Museum of Natural History, with 31 collections found to contain seeds, and a total of 543 seeds identified. We noted or measured the following aspects of each seed: platyspermic or radiospermic symmetry; number of seeds of the same type on a specimen; maximum height and width; presence or absence of a compression border; winged or unwinged; nucule and wing height and width. Results: 26 seed morphotypes were identified with approximately 52% being platyspermic and 48% radiospermic. Radiospermic seeds ranged from 1.5 cm – 0.2 cm in length and 1.0 – 0.2 mm in width; Platyspermic seeds ranged from 2.0 – 0.4 cm in length and 1.6 – 0.3 cm in width. 52% of the seeds were winged; of these one form had asymmetrical wings. From these observations, we conclude that the great majority of the seeds in the Clear Fork Group species pool were wind dispersed and most were large, by modern standards. All radiospermic seeds were small, and few appear to have had distinctive compression borders, indicative of thick, fleshy outer seed coats. The highest concentrations of single types of seeds were in deposits of actively flowing stream channels, and were primarily small and radiospermic in form. Previous studies of regional paleosols and sedimentology indicate strongly seasonal moisture distribution, with periods of high moisture availability punctuated by intervals of drought. The seed profile from these strata is consistent with such a setting and suggests seasonal reproduction and reliance primarily on abiotic vectors (wind and water) for dispersal. The generally large size of the seeds, particularly those of platyspermic symmetry, suggests little or no dormancy and small storage of seeds in soil seed pools.