Morphology, ultrastructure, and paleoecology of Paxillitriletes vittatus sp. nov. From the mid‐cretaceous (Cenomanian) of Kansas

Abstract

Large numbers of a new species of megaspore, Paxillitriletes vittatus, have been recovered through bulk maceration of a sample from the Dakota Formation (Cenomanian) of Kansas. Transmission electron microscopy has revealed a spore wall ultrastructure similar to both modern and fossil lycopod mega‐spores, consisting of a spongy reticulum of sporopollenin threads which are more compact towards the interior. The wall structure is similar to that of modern Isoetes, as well as another Mesozoic genus, Minerisporites, which has been found in situ in Isoetites megafossils. Monolete microspores, similar to those of Isoetes, were found entangled in the capilli of P. vittatus. The Paxillitriletes megaspores were found in great abundance in a dark brown, organic‐rich clay which has been interpreted sedimento‐logically as a marshy lake‐margin deposit. This abundance of a single species of megaspore suggests that the parent plants were a conspicuous part of this marsh community, similar to the habitat occupied by many species of Isoetes. The combined morphological, ultrastructural, and paleoecological evidence suggests that the systematic affinities of Paxillitriletes is with the Isoetales.