Evidence of mycoparasitism and hypermycoparasitism in Early Cretaceous amber. 2007. Ge. O. Poinar Jr. and R. Buckley. Mycological Research 111: 503-506.
From Virginia Gewin at News@nature.com:
George Poinar, an Oregon State University zoologist and president of The Amber Institute, in Corvallis, Oregon, and Ron Buckley, a registered nurse and amateur fossil hunter from Florence, Kentucky have found the oldest mushroom fossil yet, encased in amber along with a striking example of a parasite feeding upon a parasite. Dated to 100 million years ago by the age of material surrounding the amber, the mushroom joins the exclusive company of just a handful of fossilized fleshy fungal bodies ever found.
The amber also holds the remains of an ancient parasitic relationship. The sample contains a mycoparasite, or fungus growing on the mushroom, and a hyperparasite growing on the mycoparasite.
Buckley's amber fascination is also a money-making venture. He sells collectable pieces with trapped bugs or flowers on eBay, an online auction website. Over time, he's honed a sharp eye for pieces of scientific interest — which he sends to Poinar. So far, they say they have discovered the oldest-known bee, the oldest-known flowers in amber and the oldest-known ticks. Their oldest find yet is a 130 million-year-old nematode parasite of a fly.