lichen-like fossils have been found in the doushantuo formation in southern china dating back to 635–551 ma. lichens were a component of the early terrestrial ecosystems, and the estimated age of the oldest terrestrial lichen fossil is 400 ma; this date corresponds to the age of the oldest known sporocarp fossil, a "paleopyrenomycites" species found in the rhynie chert. the oldest fossil with microscopic features resembling modern-day basidiomycetes is "palaeoancistrus", found permineralized with a fern from the pennsylvanian. rare in the fossil record are the homobasidiomycetes (a taxon roughly equivalent to the mushroom-producing species of the agaricomycetes). two amber-preserved specimens provide evidence that the earliest known mushroom-forming fungi (the extinct species "archaeomarasmius legletti") appeared during the mid-cretaceous, 90 ma.