Every evening across the immense expanse of the tropical western Pacific, millions of white-shelled, dinner-plate-size mollusks begin an epic voyage. They rise from their daytime resting place—the dark, muddy ocean bottom a thousand feet or more deep—and slowly swim upward to shallow coral reefs where they feed for the night. These animals, the chambered nautiluses, look like snails with tentacles—their closest living relatives are the octopus and squid. More than that, though, they bear the look of a creature from a bygone era. Over the past 500 million years—before, during, and after the age of dinosaurs—more than 10,000 related species have roamed the seas. But in the 65 million years since the dinosaurs died out, the family to which the chambered nautilus belongs has gradually diminished. Today only a few species still exist, and they remain poorly known. Only recently have we learned some of the key facts about nautiluses, facts as simple as their extraordinary nocturnal voyages.
This new knowledge has caused paleontologists such as myself to ask new questions: Is this nightly behavior a holdover from the age of dinosaurs, when great scaly marine lizards preyed on the shelled denizens of ancient seas? And, more important, is the chambered nautilus itself only a recent descendant of an ancient lineage—or a true living fossil that actually lived during the age of dinosaurs and endured through the long roll of time unchanged?
The nautilus has commanded scientific attention at least since the time of the ancient Greeks, who were intrigued by the unique, beautiful partitions of its shell. When cut in half, the nautilus shell describes an unwinding spiral intersected with beguiling regularity by pearly chambers. In the 1600s the great English natural historian Robert Hooke received a chambered nautilus shell (even then a great rarity) and wrote the first learned treatise about its shape. Without ever seeing a live specimen, he correctly deduced that the chambers of the shell held gas rather than animal flesh and thus gave the creature buoyancy.
