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Bivalvia are a class within the phylum Mollusca more commonly referred to as bivalves or mollusks. Their shell consists of 2 hinged parts. The 2 parts are in most cases asymmetrical, but roughly can be seen as a mirror image of each other. Some Bivalves (shells) were made up from aragonite which dissolves relatively easy, fossilization in mostly limited to the preservation of a rocky core. Other bivalves (shells) were made up from calcite which shows better shell preservation after the fossilization process. Fossil bivalves are very common and cover a big timespan in evolutionary history. Fossil records date back as early as the Cambrian period and even in the present bivalves still exist. Their diversity showed an increase during the Mesozoic period.
Example of bivalve, note that the individual shell parts are asymmetrical.
Example of a bivalve, preserved as stone core.
One remarkable group of extinct, reef building bivalves are called Rudista (rudists).
Photos or locations for rudists on this site
Photos or locations for bivalves on this site
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