Two plant-fossil assemblages of early Permian age from north-central Texas and their comparison with other Permian deposits of the region

North-Central Texas preserves an early Permian record of floristic change from the Asselian through the Kungurian. The regional floras that occur during that time interval vary compositionally in systematic ways and indicate major periods of environmental change. Here we describe two such floras from the late Artinskian, found in close geographic and stratigraphic proximity, the latter collection (1991) initially was thought to be from the same site as an earlier collection (1974), but proved to be from a different layer in the same area. The two floras, "Farmer's Tank" and "Cattle Tank" were analyzed quantitatively. They are composed of the same basic mixture of taxa but with strikingly different dominance-diversity profiles; Farmer's Tank is dominated by walchian conifers with subdominant marattialean tree ferns and gigantopterids, and Cattle Tank by marattialean tree ferns with subdominant noeggerathialeans and callipterids with conifers fourth in rank. These floras are from the early phases of a change in regional floras from heavily dominated by conifers and other xeromorphic, drought-tolerant elements, to "mixed" floras rich in, even dominated by marattialean tree ferns, but retaining a major component of drought-tolerant elements. These quantitative differences may reflect differences in the environment of deposition, but also possibly in season of the year - the Farmer's Tank collection is rich in seeds of considerable variety (13 morphotypes), whereas the Cattle Tank collection contains few seeds. These floristic features strongly suggest a landscape under seasonal climatic conditions with a period of moisture deficit.