Fusulinid

Part of speech: noun

Definitions

1. A type of extinct single-celled marine organism characterized by a complex, chambered shell made of calcium carbonate, commonly found as fossils in Paleozoic and early Mesozoic sedimentary rocks, and used by geologists for biostratigraphic dating
2. Fossilized remains of a group of ancient foraminifera distinguished by their elongate, multi-chambered tests made primarily of calcium carbonate, significant in studying Earth's geological past and correlating sediment layers
3. An extinct species of microscopic marine protists noted for their intricate, multi-chambered calcium carbonate shells, often preserved in sedimentary rock and valuable for understanding stratigraphic sequences and paleoenvironmental conditions

Etymology: Fusulinids were tiny marine organisms, single-celled foraminifera with spindle- or grain-shaped shells, that lived in Paleozoic seas roughly 300 to 360 million years ago. The name comes from the genus "Fusulina," coined in 1844 by the German naturalist Hermann von Meyer, who based it on the Latin "fusus," meaning spindle, a reference to the shape of the shells. The "-id" ending, which in zoology marks membership in a family, was then added to form the group name. Fusulinids were so abundant and changed so quickly through time that geologists use them as index fossils, meaning that finding a particular species in a rock layer tells you roughly how old that layer is. Their shells often accumulated into thick limestone deposits, and some of these rocks are visible in the mountains of the western United States and parts of Asia.