Mazon Creek Crustacean Kallidecthes with Exceptional Preservation

Name: Class: Crustacea; Order: Aeschronectida; Kallidecthes richardsoni

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

Size (25.4mm=1 inch): 46 mm long Matrix: 75 mm by 57 mm

Fossil Site: Mazon Creek, Pit 11, Francis Creek shale, Braidwood, Illinois

Mazon Creek Crustacean KallidecthesDescription: The Mazon Creek deposits of the region near Braidwood, Illinois rival the other famous Lagerstatten of the Burgess Shale, Solnhofen, and Liaoning for the variety of detailed life preserved. Many exquisitely preserved specimens are found in the ironstone nodules that make up the deposits. The majority of collecting areas are the spoil heaps of abandoned coalmines, the most famous of which is Peabody Coal Pit 11. Pit 11 now serves as a cooling pond for the Braidwood nuclear power plant, but with over 100 other localities, specimens still come to light.

This specimen is of a genus that represents an entirely extinct radiation of crustaceans that went extinct, leaving the modern-day mantis shrimps as closest relatives. Large examples such as this that possess a deeper abdomen and more rectangular carapace may actually represent a distinct species. Specimens such as this that preserve the gills of the pleopods are not often seen, making this a fine example of the taxon.

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