Hippuritacea

Hippuritacea is an extinct superfamily of bivalve mollusks. These marine invertebrates are characterized by their irregular shells, which often exhibit a peculiar morphology. The superfamily is particularly notable for its rudist forms, which lived during the Mesozoic Era, specifically from the Jurassic to the Late Cretaceous periods. Rudists were sessile organisms that lived in shallow marine environments and often formed extensive reef-like structures, similar to modern corals.

The shell of hippuritaceans is typically composed of two valves, though they are often asymmetrical. One valve, the lower or fixed valve, is usually large, conical, or cylindrical, and cemented to the substrate. The upper valve, or free valve, is often much smaller and operculiform, fitting over the opening of the lower valve. This unique shell structure allowed them to live a sedentary life and possibly provided protection from predators.

Fossilized remains of Hippuritacea are found in carbonate rocks worldwide, particularly in Tethyan regions. Their abundance and the distinctive reef-building nature of many species have made them significant components of Mesozoic paleocommunities. The decline and eventual extinction of Hippuritacea occurred at the end of the Cretaceous period, coinciding with the Cretaceous-Paleogene extinction event. Their fossils are important for biostratigraphy and understanding ancient marine ecosystems.