Who would expect tropical foraminifera near Paris, France? The large pinwheels in this image are nummulites, fossil forams whose name is derived from the Latin word for coin. Well known from the limestones used in building Egyptian pyramids, nummulites are found in Tertiary deposits in France, Switzerland, Egypt, Libya and India, all areas once covered by the warm tropical waters of the ancient Tethys Sea.
Despite being single-celled protozoa, these macro-forams reached sizes of 2 cm and are suspected to have hosted symbiotic algae much like Marginopora species associated with today’s tropical reef systems. In modern species, this symbiosis is known to facilitate the deposition of the organism’s calcium carbonate test (its body). The pinwheel structure reflects growth as additional chambers are added to the perimeter of the test.