The Mazon Creek fauna is extremely
diverse. According to Nitecki (1979) more than 320 species of animal
have been identified (or originally described) from the deposit.
Scientists studying the fauna have divided it into two components.
These are the Essex and Braidwood faunas. The Essex fauna contains the
marine organisms that would have lived in the shallow bays. The Essex
fauna includes such animals as jellyfish, worms, snails, clams, shrimp,
The Braidwood fauna consists of land and freshwater-dwelling organisms
that washed into the bays. The Braidwood fauna includes insects, millipedes,
centipedes, scorpions, spiders, spider relatives, amphibians, freshwater
fish, shrimps, freshwater horseshoe crabs, and ostracodes.
The following Web pages discuss the fossil animals in the following
categories with fossil examples: