Coprinopsis laanii fruiting on mammal carcasses in an underground mine.

Fungi are important decomposers of organic material, including animal waste. Ammonia and postputrefaction fungi grow in soil enriched in ammonium and nitrogen from carcasses. In 2014, we observed mushrooms fruiting on the flesh of a dead muskrat ( Ondatra zibethicus ) in an abandoned underground copper mine in southeastern New Brunswick, Canada. We placed an adult beaver ( Castor canadensis ) carcass near the muskrat to facilitate fungal colonization and fruiting. The beaver carcass was colonized by a variety of molds, especially Acaulium caviariforme . We observed mushrooms of an unidentified copriniid on the flesh 6 years and 9 months after carcass placement. Using morphological and molecular (nuclear internal transcribed spacer [nrITS]) data, we identified the mushrooms as Coprinopsis laanii , a rarely encountered species generally considered lignicolous. We discuss the role of C. laanii , and other postputrefaction fungi, in cave environments.