The Family Belemnitidae is a group of extinct cephalopods that lived during the Mesozoic Era. They are commonly known as belemnites and are characterized by their bullet-shaped bodies and internal shells known as guards. There are various synonyms for this family, including Belemnopsida, Belemnaceae, and Dibranchiata belemnites. These synonyms reflect the taxonomic changes that have occurred over the years as researchers have gained a better understanding of their evolutionary relationships. Despite these changes, the belemnites remain a crucial group in the fossil record, providing valuable insights into the ecology and evolution of ancient marine ecosystems.