Mazon Creek Fossil Crustacean Cyclus obesus

Name: Cyclus obesus

Phylum Arthropoda; Subphylum Crustacea; Class Maxillipoda

Geological Time: Pennsylvanian (~300 m.y.a.)

Size: 16 mm long, 50 mm across Matrix: 33 mm by 37 mm

Fossil Site: Mazon Creek, Francis Creek shale, Braidwood, Illinois

Cyclus obesus fossilThe taxonomy of these animals has been under dispute ever since their discovery in the late 1800s, but they are currently believedCyclus Mazon Creek Crustacean 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.

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