A Thelypteridaceous Fern from the Early Paleocene Raton Formation, South-central Colorado, and Its Importance in Interpreting the Climate of the Region

Abstract

Based on the results of leaf physiognomic studies, it is generally acknowledged that the Raton Basin in south-central Colorado and northeastern New Mexico hosted a tropical rainforest during the early Paleocene. However, this interpretation is problematic because the canopy-forming foliage of this forest was predominately lauraceous, and lauraceous foliage is almost invariably entire-margined. Thus, it may be necessary to look to other, taxonomy-based paleotemperature proxies to test megathermal paleotemperature estimates based solely on leaf physiognomic analyses of predominately lauraceous datasets. In this study, the pantropical fern Cyclosorus sensu lato (s.l.) is reported from the upper coal zone of the Raton Formation. The presence of this fern in the understory of a predominately lauraceous canopy suggests megathermal conditions in the early Paleocene.