Silurian Reef at Thornton, Illinois
Pentamerid Brachiopods

Pentamerids are a type of brachiopod that grew to sizes of over 10 cm, and they represent one of the largest types of dwellers within Silurian reefs. A thickened beak area served as a weight to stabilize the shell in the sediment, and there was no fixed attachment. Pentamerid brachiopods often lived as clumps of individuals, as shown in this reconstruction.

Pentamerid brachiopods occur abundantly in discrete beds on the reef flanks at Thornton. The shell material has been dissolved, and the brachiopods are preserved as internal and external molds.

The abundant pentamerid brachiopod at Thornton is Kirkidium knightii, a species described originally from the Silurian of the Welsh Borderland. These photos show three views of the same shell.

© 1997, Milwaukee Public Museum, Inc.