An Early Permian flora with Late Permian and Mesozoic affinities from north-central Texas

Abstract

Early Permian (late Leonardian Series) plant assemblages from King, Knox, and Stonewall Counties of North-Central Texas are dominated by seed plants, some apparently congeneric with taxa heretofore known only from the Late Permian or the Mesozoic. Conifers are the dominant elements, including one or more species of Ullmannia, Pseudovoltzia liebeana, both known from the Late Permian Zechstein flora of Germany and England, Podozamites sp., characteristic of the Mesozoic, and Walchia sp., abundant in Early Permian floras. Locally common are Taeniopteris cf. eckardtii, a Zechstein species, an unidentified plant represented by pinnulelike laminae with fine parallel veins, similar to pinnules of some Mesozoic cycads, and calamite stems. Rarely encountered are leaf fragments of the Paleozoic ginkgophyte Dicranophyllum, flabellate ginkgophyte leaves, leaves with a broad midvein and narrow, fimbriate lamina, and Wattia, typical of the Early Permian. Associated with these foliar remains are ovulate reproductive structures including the presumed cycad megasporophyll Dioonitocarpidium, known only from the Mesozoic, a voltzialean cone scale similar to Swedenborgia, and a variety of seeds, some remarkably similar to Agathis, of Cretaceous age. The assemblage includes only rare scraps of foliage and seeds possibly attributable to the pteridophyllous elements (gigantopterids, callipterids, and ferns) that dominate the Permian. The fossil plants occur in multistorey, fining-upwards, tidal-channel deposits that also include pelecypods and fragmentary palaeoniscoid fish. The occurrence of derived lineages in xeric habitats during the Early Permian indicates that some supposed Mesozoic groups actually preceded and survived the end-Permian extinction, reappearing in basinal lowlands during the mid-Mesozoic.