First Report of Fungal Palynomorphs From the Zechstein Group (Lopingian): Implications for the Stratigraphic Completeness of the Earth's Paleozoic Fungal Record

Abstract

Palynological study of the Permian–Triassic boundary has typically focused on the pollen grain and spore content to reconstruct vegetation, with fungal remains either left unidentified or set aside for future research. Paleozoic fungal microfossil records in particular are lacking. The Zechstein Group (∼ 258–252 Ma; Lopingian) is a remarkable stratigraphic sequence of stacked carbonates and evaporites. High-resolution palynological analysis of new borehole cores through the Zechstein Group of northeast England has revealed its entire sedimentological history and enabled a new reconstruction of vegetation dynamics in central-western Europe preceding the Permian–Triassic boundary. Assemblages composed of conifers, pteridosperms, pteridophytes, sphenopsids, and cycads/ginkgoes were recovered alongside fungal remains throughout the entire sequence. Four fungal morphologies were observed, the most common being smooth-walled spheroidal inclusions of an endobiotic Chytridiomycota or Hypochytridiomycota affinity. Other evidence of fungi includes epiphytic Callimothallus-type fungi (Family Microthyraceae), the dematiaceous Chaetomium-like mold (Family Chaetomiaceae) found associated with soil, cellulose and plant debris, and possible evidence of chytrid-induced pitting on the surface of plant cuticle. This is the first study to highlight the fungal content of Zechstein palynological preparations and while occurrences are rare, they provide new insight into the composition of the Zechstein forest understory, reinforcing the interpretation that the upper Zechstein environment was humid. This work improves our understanding of the taxonomic and functional diversity of fungal taxa associated with evaporite systems during the Lopingian, and highlights the exceptional preservation potential of halite, combating underestimates of fungal richness in the fossil record.