The nautilus, a marine mollusk with a beautifully coiled, chambered shell, often appears in conversations about ancient sea life. This animal is frequently mistaken for a creature of the distant past. The confusion is understandable, given its unique, old-world appearance compared to its modern relatives like the octopus and squid.
The Definitive Answer: A Living Lineage
The simple and definitive answer to whether the nautilus is extinct is no. Several species of nautiluses are currently alive and inhabit the deep slopes of the Indo-Pacific ocean. These animals represent the last living members of the subclass Nautiloidea, a group that once flourished across the globe. The common chambered nautilus (Nautilus pompilius) is the most well-known species, but at least seven to nine extant species across two genera, Nautilus and Allonautilus, are recognized by scientists today.
Anatomy and Behavior
The nautilus possesses a remarkable structure that allows it to thrive in its deep-water environment, centered on its external, spiral shell. This shell is divided internally into numerous gas-filled compartments called the phragmocone, with the animal’s body residing only in the largest, outermost chamber. A specialized tube called the siphuncle runs through all these chambers, actively regulating the balance of gas and water to control the animal’s buoyancy, much like the ballast tanks of a submarine.
The nautilus extends a crown of approximately 90 tentacles from its shell opening, far more than any other cephalopod. These tentacles are unique because they lack suckers, instead using ridges and a sticky secretion to grip prey and food. For movement, the animal uses a method called jet propulsion, forcefully expelling water from a funnel-like siphon to maneuver through the water. Nautiluses are primarily found at depths between 160 and 2,000 feet, where they spend their days and ascend to shallower waters at night to scavenge for crustaceans and carrion.
Deep Evolutionary History
The belief that the nautilus is extinct stems from its immense geological age and the concept of it being a “living fossil.” This designation reflects that the animal’s basic body plan has changed very little over hundreds of millions of years. The earliest nautiloids appeared in the Late Cambrian period, making the lineage approximately 500 million years old.
The nautilus is the sole survivor of a vast group of ancient shelled cephalopods, including the entirely extinct ammonites and belemnites. Ammonites, which were incredibly diverse, failed to survive the mass extinction event at the end of the Cretaceous period 65 million years ago. The nautilus, uniquely, survived all five of Earth’s major mass extinctions, maintaining the ancestral trait of an external shell while its relatives evolved into modern, shell-less cephalopods like octopuses and squid.
Modern Vulnerability
Despite its survival through eons of environmental change, the nautilus now faces severe modern threats, primarily from human activity. The greatest danger is overfishing, driven by the international trade in their highly attractive, coiled shells for jewelry and curios.
Nautiluses possess life history characteristics that make them exceptionally susceptible to population collapse. They have a remarkably long lifespan for a cephalopod, maturing slowly, sometimes taking 10 to 17 years to reach sexual maturity. Their reproductive rate is also very low, with females laying only a small number of eggs at a time, unlike the mass spawning of squid and octopus. This combination of slow growth and low fecundity means that populations cannot quickly recover from heavy fishing pressure, leading to localized extinctions in some areas of the Indo-Pacific. Due to these threats, the chambered nautilus has been listed as a threatened species under various conservation assessments.