The frilled shark, Chlamydoselachus anguineus, is a surviving species inhabiting the deep ocean today. Its rare sightings and highly unusual appearance have earned it the title of a “living fossil.” This ancient lineage possesses an elongated, dark body that resembles a large eel more than a typical shark. The species represents one of the most primitive shark forms still alive, providing a unique look at the evolutionary past of apex predators.
Where Frilled Sharks Live
This species inhabits the outer continental shelf and upper continental slope, typically dwelling in the bathypelagic and upper abyssal zones. Frilled sharks are usually found at depths between 120 meters and 1,500 meters, though their occurrence is highly irregular across their range.
The species has a widespread but patchy global distribution, occurring in both the Atlantic and Pacific Oceans. Specific areas include the waters off Norway, Ireland, and Namibia in the Atlantic. In the Pacific, they are found near Japan, Australia, New Zealand, and off the coasts of California and Chile. Sightings are infrequent, often occurring only when the animal is accidentally caught as bycatch in deep-sea trawling nets.
Defining Features and Ancient Ancestry
The frilled shark’s body shape is long and slender, reaching up to two meters in length. Its fins are positioned far toward the tail, emphasizing its serpentine form. The body color is a uniform dark brown or grey, which offers excellent camouflage in the low-light environment of the deep sea.
One defining, primitive characteristic is the number of gill slits; the frilled shark possesses six pairs, unlike the five found on most modern sharks. The first pair extends across the throat, connecting underneath the head. The extended tips of the gill filaments create a ruffled margin, and this unique, fringe-like structure is the origin of the common name.
The mouth is positioned terminally at the end of the snout, instead of underneath like most other sharks, and it is lined with approximately 300 needle-sharp teeth. Each tooth is trident-shaped, possessing three slender, backward-pointing cusps designed for snagging and holding prey. These physical traits, including the gill structure and the jaw articulation, bear a remarkable resemblance to fossilized shark relatives dating back to the Late Cretaceous period, nearly 80 million years ago. This morphological conservatism is why the frilled shark is referenced as a “living fossil.”
Unique Hunting and Reproductive Methods
The frilled shark’s deep-sea ecology requires a specialized approach to hunting, compensating for its relatively weak swimming ability. Instead of chasing fast-moving prey, the shark employs an ambush strategy. It is hypothesized that the shark coils its body like a spring before launching a rapid, snake-like lunge to engulf its victim.
Its diet consists primarily of soft-bodied, slippery prey like deep-sea squid, along with various bony fishes and other smaller sharks. The wide gape of its mouth, combined with hundreds of inwardly curved teeth, allows it to secure and swallow prey that can be surprisingly large relative to its own size.
The reproductive cycle of the frilled shark is one of the most unusual among all vertebrates. The species is ovoviviparous, meaning the embryos develop within egg capsules inside the mother’s uterus, where they are nourished by a yolk sac rather than a placenta. The most extraordinary detail is the gestation period, which is estimated to last up to three and a half years, representing the longest pregnancy known for any vertebrate animal. This extremely slow reproductive rate results in small litters, typically yielding between two and fifteen fully developed pups.