Cephalopods: 500-million-year-old Mollusks (PA-04)
Squid, octopus, and cuttlefish are living relatives of animals that were once major predators of the seathe cephalopods. Ancient cephalopods had shellsy divided into chambers that enabled them to control their buoyancy in water.

Fossil cephalopods, while always chambered, are found in many shapes. Some are a straight cone as much as 19 feet long; others are coiled into a spiral. The largest coiled cephalopod had a shell as large as a wagon wheel. The most successful were ammonites, which became extinct about 60 million years ago. Fossil cephalopods, especially common in the Laurel Limestone of southeastern Indiana, are a key guide for correlating rocks around the world.

Our Hoosier State Beneath Us: Paleontology