Ctenis clarnoensissp. n., an Unusual Cycadalean Foliage from the Eocene Clarno Formation, Oregon

Abstract

Premise of research. Leaves of an extinct kind of cycad are recognized from the middle and late Eocene Clarno Formation of Oregon. Although the pinnately compound leaf is similar in gross form and organization to some other extant and Cenozoic cycads such as Dioon Lindl., Encephalartos Lehm., and Dioonopsis Horiuchi et Kimura, it is readily distinguished from them by its venation, consisting of a closed reticulum of a single order of veins with a frequent dichotomizing and anastomosing pattern. Methodology. Fossils stored in the Museum of Paleontology (University of California), Florida Museum of Natural History (University of Florida), and Condon Museum of Natural History (University of Oregon) were studied applying conventional macromorphological and micromorphological methods including transmitted light and epifluorescence microscopy. Pivotal results. The leaves conform in their peculiar venation and epidermal anatomy to the extinct genus Ctenis Lindley et Hutton, which previously was known only from Mesozoic occurrences. Ctenis clarnoensis Erdei et Manchester sp. n. adds to the diversity of cycads known from the Paleogene of western North America. Conclusions. The record of the reticulate-veined C. clarnoensis and other fossil cycad genera with anastomosing venation patterns from the Paleogene implies that an extinct lineage or lineages of cycads sharing the character of reticulate venation, previously considered to be restricted to the Mesozoic, may have persisted into the Paleogene. Some physiognomic features of leaflets including the involute margin and pointed apex may suggest periodically dry conditions. By the present record the stratigraphic range of Ctenis is significantly extended from its previously known latest records in the Early Cretaceous up to as late as the Eocene.