Abstract
The various types of spherical microfossils collectively termed fossil fungal “sporocarps” exhibit basic congruities in morphology that have been used to suggest they all may belong to the same higher taxonomic category. Both the Ascomycota and zygomycete fungi have been discussed in this respect, but features that precisely delimit the nature and taxonomic position of these fossils have not been documented. Here, we present two new specimens of the Pennsylvanian “sporocarp” Sprocarpon asteroides from the Lower Coal Measures of Great Britain. Both provide evidence that a spore with a multi-layered wall was formed in this structure by blastic inflation of a hyphal tip. The outer spore walls appear to be continuous with the wall of the subtending hypha, while the inner wall (the spore wall proper) more likely developed de novo. Sporocarpon asteroides is interpreted as a unisporic sporocarp with a pseudoparenchymatous peridium, likely with affinities to the Glomeromycota. This discovery supports the notion that the fossil fungal “sporocarps” include several biologically different structures.