Fossil ascospores of Potamomyces from the Early Pliocene Gray Fossil Site (USA)

Fossil fungal ascospores assignable to the genus Potamomyces have been recovered from Early Pliocene deposits at the Gray Fossil Site, a Fossil-Lagerstätte in Tennessee, USA. Characterized by four prominent equatorial verrucae, these ascospores closely resemble the fossil-species Potamomyces invaginatus , P . batii , and P . pontidiensis , as well as the extant species P . armatisporus . Modern species of Potamomyces are primarily saprotrophic fungi that occur on decaying wood in freshwater and brackish environments, as well as in moist terrestrial habitats. During the Pliocene, Potamomyces formed part of the late Neogene wetland ecosystem associated with sinkhole ponds at the Gray Fossil Site, which developed under a warm temperate to subtropical humid climate. The remains described here represent the northernmost known occurrence of Potamomyces in North America, based on both fossil and extant records. These findings further suggest that Potamomyces appears to have considerable potential as a non-pollen palynomorph proxy for reconstructing past environments and climates.