Wisconsin Public Day has an article about fossils from Waukesha County, including a the oldest known leech in the fossil record. The fossil deposit is commonly referred to as the Waukesha Lagerstätte. A few years ago, researchers found the world’s oldest fossilized scorpion at the site.

The Waukesha Biota, also known as the Waukesha Lagerstätte, is special because it holds a mass amount of paleontological information. It is preserved at the museum as a 12-centimeter thin layer of mudstone filled with rare fossils of soft-bodied organisms. 

Today most of the original biota is gone, but researchers are still making new discoveries from the museum’s collection. The most recent: a leech, older than dinosaurs, that preyed on living organisms.

It is the oldest leech fossil ever found. The finding pushes the species’ initial origins back 200 million years.

Carrie Eaton is the museum’s curator and has managed over 150,000 specimens. She says the biota is one of a kind. 

“The diversity of species from this site and their high quality of preservation offers this really rare glimpse into this window of geologic time,” Eaton said.