Fish
Frilled Shark
Chlamydoselachus anguineus · also called lizard shark, living fossil shark
The frilled shark looks less like a shark than like a sea serpent — a long, brown, eel-bodied fish with a wide, forward-set mouth full of glassy trident teeth. It lives in the deep sea, it has barely changed in tens of millions of years, and it may be pregnant for longer than any other vertebrate.
Overview
Frilled sharks live in deep water worldwide — on the outer continental shelves and upper slopes, generally between about 500 and 1,500 metres, near the seabed and in the water column above it. Encounters are rare and scattered across the Atlantic, Pacific, and Indian Oceans, and most specimens come from fishery bycatch or from sick animals that rise toward the surface. Live footage exists but is very limited.
A shark from the age of dinosaurs
The frilled shark is one of the animals most often labelled a “living fossil,” and for good reason: its overall form closely matches shark relatives from around 80 million years ago, and it keeps a suite of ancient features that other sharks lost —
- an eel-like body with the fins pushed to the rear,
- a terminal mouth at the front of the head,
- six pairs of gill slits (most sharks have five), the frilly first pair fused across the throat — the “frill,”
- a persistent notochord only partly replaced by vertebrae,
- and simple, three-pointed teeth in about 25 rows.
How it feeds
Its hunting style is inferred rather than observed. The long, flexible body could be coiled and released like a striking snake, and the widely opening, forward-set jaws let the shark take prey up to half its own length. The 300 recurved trident teeth work as a one-way trap for soft-bodied deep-sea squid — the shark’s main food — and for fish and small sharks, which are swallowed whole.
Extremely slow reproduction
Frilled sharks are live-bearers, and the cold, food-poor deep sea slows everything down. The gestation period is estimated at up to 3.5 years, perhaps the longest known for any vertebrate, and litters are small. Pups are around 55 cm at birth and fully independent.
Status
The frilled shark is listed as Least Concern — it is widely distributed and there is no evidence of a major decline — but this rating carries real uncertainty, because the species is so rarely seen that its population and trends are essentially unknown. Its extremely slow reproduction means it would recover very poorly from heavy fishing pressure, and deep-sea trawling and longlining that reach its habitat are the main potential threats.
Frilled Shark: common questions
Why is the frilled shark called a "living fossil"?
Its body plan is very close to that of shark relatives from around 80 million years ago, and it retains a mix of primitive features — an eel-like body, a mouth at the front of the head rather than underneath, six gill slits instead of the usual five, a notochord (a flexible rod) that is not fully replaced by vertebrae, and simple trident teeth. Most sharks evolved away from this arrangement long ago, but the frilled shark's lineage changed little, probably because the deep sea it lives in is a stable environment.
How does a frilled shark catch prey?
It is thought to hunt by lunging, snake-style. The shark can flex its long body into an S-shape and then strike forward, and its jaws are set far forward and can open extremely wide, so it may engulf prey up to half its own length. The 300 inward- and backward-pointing three-pronged teeth act like a net of hooks — once a soft-bodied squid or fish is in the mouth, the teeth make it almost impossible for it to back out. Slow-moving or exhausted deep-sea squid are the likely main target.
Is the frilled shark dangerous to people?
No. It lives hundreds of metres down, is small, slow, and not aggressive, and there is no record of one harming a person. The teeth are needle-sharp and could cut a careless hand on a hauled-up specimen, but the shark poses no threat in its own habitat. It is occasionally caught as deep-sea fishery bycatch and very rarely filmed alive, usually when a dying individual drifts up to shallow water.
How long is a frilled shark pregnant?
Possibly longer than any other backboned animal. The frilled shark is aplacental viviparous — the embryos develop inside the female nourished by yolk — and because the deep sea is cold and food is scarce, development is extremely slow. The gestation period has been estimated at up to about 3.5 years, and litters are small, typically 2 to 15 pups. This makes the species very slow to replace losses.