The early fossil record of glomeromycete fungi: New data on spores associated with early tracheophytes in the Lower Devonian (Emsian; c. 400 Ma) of Gaspé (Quebec, Canada)

Abstract

Fossil assemblages in the fluvial to coastal deposits of the Early Devonian Battery Point Formation (400–395 Ma; Gaspé Bay, Quebec, Canada) are among the most diverse occurrences of Early Devonian permineralized plants worldwide. The plants host microbial and fungal material, which was studied in cellulose acetate peels and thin sections. The fossil fungal material includes spores that show affinities to the Glomeromycotina, preserved in trimerophyte axes. The spores fall into two size categories, both characterized by complex wall layering and hyphal attachments. Spores in the small category (40–65 μm) occur in a single axis and exhibit few informative features. The most frequently occurring type is the large spores (90–240 μm) that are placed into the new species Glomites oqoti. These spores exhibit four wall layers (when well preserved), of which two are always present: a thick, dark layer and a thin, membranous layer. Several lines of circumstantial evidence suggest that the spores were metabolically active within their plant hosts at the time of fossilization and that the plants were alive at the time of colonization. These observations, along with comparisons with other fossil glomeromycetes and the life history traits of living glomeromycetes, suggest that G. oqoti held an endomycorrhizal role. The Battery Point Formation fossils represent the only Early Devonian glomeromycete occurrence documented outside the Rhynie Chert hot spring deposits. Their occurrence in fluvial-coastal environments and their putative mycorrhizal role suggest that glomeromycetes were relatively ubiquitous symbionts of tracheophytes, like their extant counterparts, by the Early Devonian.