Description

Pennsylvanian
Francis Creek Shale
Pit 11, Will Co., IL, USA
8mm isopod in 19mm paired concretion.
Isopod, Mazon Creek.

Isopods are an order of crustaceans with genera that live in saltwater, freshwater, and even on land.  They are uncommon in the fossil record, dating back to the Carboniferous Period .  Biologists have studied modern ones the size of a lobster from the depths of the ocean but most are small like the “pill bugs” you found in your grandparents’ garden.

This specimen appears to be an isopod.  If it is, it represents the earliest occurrence of the group.