A study of the morphology of the spore genus AncyrosporaRichardson

Abstract

Fossils assignable to the genus Ancyrospora Richardson have been recovered from Devonian strata of Iowa and Missouri. The Scanning Electron Microscope (S.E.M.) has been used to examine them and has made it possible to interpret details of spore morphology not previously recognized. The genus Ancyrospora was established in 1960 for fossils from the Cromarty nodule beds of the Middle Old Red Sandstone. Photographs and diagrams of the type species of Ancyrospora illustrate the presence and specific pattern of “numerous minute wrinkles”. Subsequent species described by Richardson (1962) show a similar condition. S.E.M. studies show the outer exoexine to be lamellar and the inner exoexine to consist of a netlike or a spongy layer. The inner exoexine may exhibit thinning on the proximal face in a manner that is consistent within observed forms. The inner exoexine is produced laterally to form a flange. The “wrinkles” are an optical representation of the inner exoexine character and exhibit two different patterns. Forms comparable to Ancyrospora grandispinosa Richardson, 1960 and A. ancyrea Eisenack Richardson, 1962 have been recovered from strata collected in Iowa and considered to be the Solon Member of the Cedar Valley Formation. The “wrinkles” of these forms are optical sections of elongated bars of a netlike inner exoexine. Individual bars of the network protrude at various points along the surface. Two or more elongate in a bundle then fuse at the tips. After fusion, two rods may recurve in the characteristic bifurcate form or the column may extend some distance before bifurcating. In optical section, the spines appear clear beyond the point of fusion which corresponds to the point where the wrinkles terminate. Fossils comparable to A. simplex Guennel, 1963 recovered from the Calloway Formation of Missouri indicate a basic form much like those of the Solon.