THE PREHISTORIC SPIRAL

❃ Ammonites were an extraordinarily successful group of marine animals that inhabited Earth's oceans for more than 300 million years. These extinct cephalopods were relatives of modern squid, octopuses, cuttlefish, and nautiluses, but are best known for their beautifully coiled shells. Appearing long before the dinosaurs, ammonites survived several mass extinctions before finally disappearing around 66 million years ago.

❃ Inside an ammonite's spiral shell was a series of chambers. As the animal grew, it constructed larger chambers and sealed off the older ones behind it, occupying the outermost chamber with its soft body and tentacles. The internal chambers likely helped regulate buoyancy, allowing ammonites to move through ancient seas while searching for prey and avoiding larger marine predators.

❃ Ammonites ranged from species only a few centimeters across to giants with shells approaching 6 feet (2 meters) in diameter. Their hard shells fossilized exceptionally well, and their rapid evolution and widespread distribution make ammonite fossils particularly valuable to scientists for dating ancient rock layers. From prehistoric oceans to museum collections today, their unmistakable spiral remains one of the most iconic shapes in the fossil record.