Coils of time

It's not easy studying the nautilus, a creature that lurks in the depths of the ocean and emerges only at night to prowl the coral reefs. But the rewards are great: discovering just how old living fossil can be.

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 day-time 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 millions 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.

Centuries would pass before other scientists could observe the chambered nautilus alive in the wild and begin to learn its secrets. The nautilus looks like nothing familiar: it swims just above the seafloor, moving like a peculiar fish; it has tentacles and a jet propulsion system somewhat like those of other cephalopods--the class of mollusks that also includes octopuses, cuttlefish, and squid. But there are great differences. The chambered nautilus has about 90 tentacles rather than the Y or 10 of other cephalopods, and its peculiarly primitive eye lacks a true lens. And no other cephalopod has anything remotely resembling the nautilus shell. The animal itself is housed in the last chamber in the shell's spiral, with only its head and many tentacles visible. As the nautilus grows, it adds a new chamber and moves into it, leaving the old one behind.

In 1975, I made the first of what turned out to be annual trips to the Western Pacific to study these odd creatures. My first goal was to observe the chambered nautilus in its natural environment along the seaward edges of coral reefs. In New Caledonia, where my studies began, local fishermen reported seeing them in the shallowest reef regions at night, but never during the day. Like the neighboring Great Barrier Reef of Australia, the immense New Caledonian reefs form great vertical walls extending down many hundreds of feet from the warm surface of the coral sea to the cold, dark, muddy bottom. During daylight hours, the nautiluses lurk in these depths, out of sight and danger from shell-breaking predators such as turtles and triggerfish. But with the coming of night, as the faint daytime light reaching the thousand-foot depths fades to complete blackness, they begin to stir. They follow the slope of the bottom toward shallower water, swimming just above the mud, sand, and coral rubble, eventually reaching the sheer vertical rocky walls that mark the base of the reef itself. Undeterred by these great coral skyscrapers, whose tops may still be 500 feet overhead, the nautiluses continue their voyage, ascending like silent hot-air balloons. Finally, after journeying for several hours, they arrive in the shallows and spend the night roving the reef, using their sense of smell to find carrion, lobster molts, and hermit crabs. With the first approach of daylight, they swim back over the reef walls and fall down into darkness.

Starting from Noumea, the capital city of New Caledonia, my colleagues and I would travel the 12 miles across the wide lagoon, through the heavy afternoon waves whipped up by the trade winds. We would arrive at the seaward side of the barrier reef just before sunset, about the time the nautiluses, far beneath us, would begin their journeys. Anchoring our boat, we shone large underwater lights to mark its position; in the utter blackness of the tropical night, we'd need to find it after our long, deep dives. Finally, at about 8 P.M., we would splash into the darkness and follow our beams of light down into the sea.