Thursday, 11 July 2019


Platryachella sp. / Devonian Brachiopod
This fellow is Platyrachella sp. a brachiopod from Middle Devonian deposits of the renamed the Little Cedar Formation, Cedar Valley Group (probably out of the Solon Member) near Benton County, deep in the agricultural belt of east-central Iowa.

Driving through Benton you see long, gently rolling slopes, farms of corn and soybean growing in deep black soil.

Benton also has three very productive quarries that produce limestone, gravel and clay for industrial uses. While the quarries focus on the commercial aspects of the many varieties of limestone produced there, they also boasts some very nice macro fossils like the brachiopod specimen you see here. While brachiopods share some similarities with their molluscan friends they are in a phylum all their own. Clams or bivalves are molluscs, the second-largest phylum of invertebrates with about 85,000 extant species.

Brachiopods are small marine shellfish that are not so common today but back in the Palaeozoic they were plentiful the world over. The two valves that make up a brachiopods shell are of different sizes and if you look closely you'll see that the hinge runs top and bottom  -- versus left and right like a clam.

Brachiopods have been with us a long time. Their lineage dates back to the Cambrian with over 12,000 fossil species and 350 living species sorted between 6,000 genera. There are two major groups of brachiopods, articulate with toothed hinges and simple open and closing muscles to manipulate their shells and inarticulate brachiopods with untoothed hinges and a more complex set of muscles used to control the brachial supports used to open and close their shells. This specimen is 7cm long and about 2.5cm deep