Recently, I found three interesting clam shell fossils on the shore of Lake Michigan, in Southwestern Michigan USA. The first sample shown, clearly reveals the hardened muddy sediment that has completely encrusted its shell.

The clam fossil below has been completely replaced by minerals and is petrified to stone. It’s the mold of the original clam shell where sediment filled in the space where the animal’s soft body parts once lived. The smooth surface is a telltale demonstration of Lake Michigan’s sand and wave action.

With the use of two abductor muscles, bivalves or clams, can open and close their shells tightly. Very fittingly, the word “clam” gives rise to the metaphor “to clam up”, meaning to stop speaking or listening.

AGES: Clams have occupied Earth beginning as early as the Cambrian Period, 510 million years ago, but were especially abundant during the Devonian Period around 400 mya.

Clam Classification

Kingdom:    Animalia

Phylum:     Mollusk (Invertebrate animals with soft body encased in hard shell i.e. squid, snails, clams, chitons, octopus, nautilus)

Class:       Bivalve or Pelycopod (Animals possessing two uneven halves called valves which are mirror images of each other joined at one edge by a hinge (i..e. oysters, mussels, scallops, clams) 

Check out one of two of my articles Curious Collectors of Clam Shells from Arks to Tellins which describes and displays beautiful photos of 19 modern day species.

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