The nautilus is still alive, thriving today as a unique marine cephalopod that carries its spiraled shell throughout its life. This creature belongs to a lineage that has spanned an immense stretch of geological time, making it one of the ocean’s most remarkable survivors. The nautilus is the only cephalopod—a class that includes octopus and squid—to retain a hard, external shell, which is used for buoyancy control. It maintains a deep-water existence, primarily in the Indo-Pacific region.
The “Living Fossil” Status
The question of the nautilus’s existence is common because the animal is widely known as a “living fossil,” a term indicating its striking resemblance to ancestors that lived hundreds of millions of years ago. The nautilus lineage, the nautiloids, first appeared in the fossil record around 500 million years ago, during the Cambrian period. They survived multiple mass extinction events that wiped out the vast majority of other life forms.
This incredible endurance is due to a phenomenon called morphological stasis, meaning the animal’s physical form has remained largely unchanged over eons. The coiled, chambered shell seen in modern nautiluses is nearly identical to that of their ancient relatives. The nautilus represents the last surviving genus of the ancient order Nautiloidea, unlike their extinct cousins like the ammonites, which vanished at the end of the Cretaceous period.
Nautilus Anatomy and Deep-Sea Habitat
The defining feature of the nautilus is its large, smooth shell, which is partitioned into approximately 30 to 36 internal chambers as the animal grows. The nautilus only occupies the outermost chamber, and the other sealed compartments are used to manage its position in the water column. A tube-like structure called the siphuncle runs through all the chambers, regulating the balance of gas and fluid to achieve perfect neutral buoyancy, similar to a submarine’s ballast tanks.
Unlike other modern cephalopods, the nautilus has a large number of tentacles, roughly 90 of them, which lack suckers. These prehensile appendages are coated in a sticky substance, used to capture prey and scavenge for food on the ocean floor. The animal moves slowly using jet propulsion, expelling water through a funnel to maneuver backward and make turns.
The nautilus is a deep-water dweller, spending most of its time in dimly lit tropical waters of the Indo-Pacific Ocean, often at depths between 500 and 2,000 feet. While they are typically found near the bottom during the day, they undertake slow vertical migrations at night to shallower waters around 250 feet to forage. Their distribution is restricted to specific parts of the western Pacific and coastal Indian Ocean, where they inhabit deep slopes and coral reefs.
Conservation Concerns
Despite their millions of years of survival, modern nautilus populations face significant threats from human activity. The primary danger is targeted overfishing, driven by the strong international demand for their shells, which are sold as curios and jewelry. The spiraled shells are often harvested to supply a global trade that has led to substantial population declines in some areas.
The life history of the nautilus makes it extremely vulnerable to this exploitation because they reproduce very slowly. They take a long time to reach sexual maturity, often over 10 years, and females lay only a small number of eggs annually. This low reproductive output means that populations are slow to recover. Due to these pressures, the chambered nautilus and other species were listed in CITES Appendix II, which mandates that international commercial trade must be monitored and sustainable.