Mazon Creek Fossil Crustacean Cyclus obesus

The taxonomy of these animals has been under dispute ever since their discovery in the late 1800s, but they are currently believed to have the copepods as nearest relatives. They have been thought to have possibly parasitized fish, but their association with plant matter seems more indicative of the habits of crabs. Normally, only the shell is preserved, but here the long antennae and some appendages are clearly evident, making this a very high-quality specimen.