Radiolitidae

Radiolitidae is a family of extinct bivalve mollusks that lived during the Cretaceous period. These animals are commonly known as rudist bivalves, a group characterized by their irregular shells and their habit of cementing one valve to the substrate. Radiolitids were particularly successful and widespread, found in marine environments across the globe.

The shells of radiolitids are typically thick and calcitic. The lower valve, which was attached to the seafloor or other organisms, was often large, conical, or irregularly shaped. The upper valve was usually smaller and operculiform, meaning it acted like a lid. A distinctive feature of many radiolitids is the presence of internal radial ribs, which are extensions of the shell material into the interior cavity. These ribs gave the family its name, derived from the Latin word "radius" meaning ray or spoke.

Radiolitids played a significant role in Cretaceous ecosystems. They often formed extensive shell beds and reefs, providing habitat for other marine life. Their abundance and rapid growth suggest they were important reef-builders of their time, comparable to modern corals in some environments. The diversity within the Radiolitidae family is considerable, with numerous genera and species described, reflecting their evolutionary success during the Mesozoic Era. Their extinction at the end of the Cretaceous, along with many other groups of organisms, marks the end of their geological record.