Ron Buckley, a nurse and photographer in Florence, Ky., who collects fossil amber, first spotted the 100-million-year-old mushroom last year. He sent the sample to George Poinar, a retired University of California professor living in Oregon, who confirmed the mushroom and found two parasites, one eating the mushroom and the second eating the other parasite.
"I was amazed enough with the mushroom," Poinar told The (Portland) Oregonian. "But then seeing the parasites was astonishing. No one has ever seen this three-tier association before."
Poinar and Buckley described the find in Mycological Research. The oldest previously known mushroom fossils dated back about 80 million years.
Mushroom fossils are extremely rare because they have no hard parts.