nummulite

A nummulite is a genus of large, flat, lenticular (lens-shaped) amoeboid protists that are characterized by a complex shell called a test. These fossil microorganisms, belonging to the phylum Foraminifera, are abundant in the fossil record, particularly in rocks from the Eocene and Oligocene epochs. Nummulites are often found in shallow marine environments. Their name comes from the Latin word "nummus," meaning coin, due to their resemblance to small coins.

The test of a nummulite is typically circular or oval in outline and can range in size from a few millimeters to several centimeters in diameter, with some specimens exceeding 10 centimeters. The test is composed of calcium carbonate and is built up of numerous chambers arranged in a spiral pattern. These chambers were occupied by the organism's cytoplasm. Nummulites lived a benthic lifestyle, meaning they lived on the seafloor.

Fossils of nummulites are widespread, especially in the Tethys Sea region, which was a large ocean that existed between the supercontinents of Gondwana and Laurasia during the Mesozoic and Cenozoic eras. They are particularly common in the limestones of the Middle East, the Mediterranean, and parts of Asia. Their presence in these rocks is an indicator of shallow, warm marine conditions. Due to their distinctive shape and abundance, nummulites have sometimes been mistaken for fossils of larger marine animals or even as coins dropped by ancient armies.