hippuritaceans

Hippuritaceans were a diverse and widespread group of extinct bivalve molluscs that lived during the Cretaceous period. They are characterized by their distinctive conical or curved shells, which often grew to be quite large. These organisms were primarily reef-builders, forming extensive shell banks and contributing significantly to the marine ecosystems of their time. Their shells typically had a thick, calcitic composition and were often cemented to the substrate or to each other, creating complex structures.

The internal morphology of hippuritaceans was also unique. They possessed a large, opaque white shell chamber and a smaller, often darker, pallial chamber. This dimyarian condition, where two adductor muscles were present, allowed them to tightly close their shells. Fossilized remains of hippuritaceans are common in Cretaceous limestones and marls worldwide, providing valuable insights into ancient marine environments and the evolution of bivalve life. Their extinction at the end of the Cretaceous period marks a significant event in molluscan history.