Cephalopods: 500-million-year-old Mollusks (PA-04)
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