The Great Survivors
For half a billion years, the nautiloids were masters of survival. First appearing in the Late Cambrian, they outlasted planetary catastrophes that annihilated countless other species. They witnessed the rise and fall of the dinosaurs and survived the asteroid impact that ended the Cretaceous period. Their secret weapon was a biological feature: a multi-chambered shell. By regulating the gas and liquid in these sealed chambers via a tube called a siphuncle, they could precisely control their buoyancy, much like a modern submarine. This allowed them to migrate vertically through the water column, escaping predators and unfavorable conditions.
Over hundreds of millions of years, they diversified into over 2,500 known fossil species, from giant straight-shelled orthocones to the familiar coiled forms. They weathered the End-Ordovician, Late Devonian, End-Permian ("The Great Dying"), End-Triassic, and Cretaceous-Paleogene mass extinctions. While their close relatives, the ammonites, vanished 66 million years ago, the nautiloids persisted, a lineage of living fossils seemed indestructible.
A New Kind of Predator
The nautiloids' long run began to end during the Oligocene epoch, starting around 30 million years ago. A new form of predator entered the oceans: the pinnipeds, the group that includes seals, sea lions, and walruses. While whales had appeared millions of years earlier, their feeding strategies did not pose an existential threat to the nautiloids. The pinnipeds were different. They had evolved a ruthlessly efficient hunting method known as pierce-feeding. Using sharp, conical teeth, they could puncture the nautiloid's living chamber, bypassing the shell's formidable defenses against crushing force.
The fossil record tells a clear story: as pinnipeds spread from their origins in the North Pacific and North Atlantic across the world's coastlines, nautiloid fossils disappeared from the same regions. One genus, the fast-swimming Aturia, held on for millions of years longer, but eventually, it too vanished. Today, the last six species of nautilus are confined to the deep slopes of the tropical Indo-West Pacific. It is the one marine region on Earth with no native seal populations, a refuge from the predator they could never out-evolve.