Reconstruction of a cyathiform Eugonophyllum, Upper Pennsylvanian, Palo Pinto County, Texas

Abstract

Species of Eugonophyllum (Codiaceae, Chlorophyta) have traditionally been characterized as phylloid or leaf-like. But a reconstruction of well preserved specimens of Eugonophyllum, probably E. johnsonii Konishi and Wray, from Upper Pennsylvanian limestone formations of Palo Pinto County, Texas, indicates it was cyathiform or cup-shaped. Reconstruction was based on the forms of membranes as seen in sections and on partial excavation of thalli. This Eugonophyllum shared with congeneric species of Eugonophyllum the characteristic two-layered cortex (outer and inner), and with other codiaceans the same general membrane structure consisting of bilateral cortices with palisades of utricles now filled with micrite, and a medulla of tubular coenocytes, an area now mostly filled with mosaic sparry calcite. A cyathiform thallus would have inner and outer cortices but no differences were found in the structure of the inner and outer cortical utricular casts. The thalli were apparently anchored with elongated, cylindrical holdfasts. Internal spherical structures, presumably developed from differentiated utricles, may have been zygotes or young embryos from an oogamous fertilization. These were apparently released to the environment through the membrane.