Mazon Creek Polychaete Worm Fossil with Preserved Jaws

Name: Fossundecima konecniorum

Phylum: Annelida; Class Polychaeta

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

Size: 34 mm long on a 40 mm by 35 mm nodule

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

Fossundecima konecniorum fossil wormDescription: The Mazon Creek deposits of the region near Braidwood, Illinois rival the other famous Lagerstatten such as the Burgess Shale, Solnhofen, and Liaoning for the diversity of organizsms. Many exquisitely preserved specimens are found in the ironstone nodules that make up the Mazon Creek flauna and flora. The majority of collecting areas are the spoilage monunds of abandoned coal mines, the most famous of which is Peabody Coal Pit 11. Pit 11, for short, is now a cooling pond for the Braidwood nuclear power plant, but with more 100 other localities making up the fossil site, specimens still are discovered. Polychaete Worm Fossil

The Polychaeta (or Bristleworms) that is shown here have a diverse representation among Mazon Creek specimens. The segmented bodies of the Polychaeta have paired lobes called parapodia which have a function in locomotion or respiration. The parapodia bear numerous bristles which are the source of the name of the class (Polychaeta means many bristles). This one was surely a predatory species, as are many modern-day bristleworms, based on the formidable pair of jaws it possessed (the common name is “jaw worm”) that were mounted in an evertible proboscis. Note the distinct jaws in the close up picture above.

click fossil pictures to enlarge

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