The largetooth cookiecutter shark (Isistius plutodus) is a small deep-water shark of the kitefin family, reaching about 42 cm (17 in), which feeds by gouging round plugs of flesh from much larger animals. It has a cigar-shaped brown body, a blunt head with big forward-facing eyes, no anal fin, and enormous triangular lower teeth, proportionally the largest of any living shark.
It bites tuna, billfish, other sharks, squid, dolphins and whales, leaving a clean crater with parallel grooves. Reproduction is assumed to be yolk-sac viviparous, but no pregnant female has been described and litter size, growth and lifespan are unknown. The IUCN listed it Least Concern in 2024, and it has never been recorded biting a person.
- Maximum length42 cm (17 in), the largest a mature female
- WeightNo reliable measurement; a few hundred grams
- LifespanUnknown; no ageing study exists
- Depth rangeUsually 60–200 m (200–660 ft); one record near 6,440 m
- DietFlesh bitten from larger fish, squid and marine mammals
- IUCN statusLeast Concern (assessed 2024)
- Kingdom
- Animalia
- Phylum
- Chordata
- Class
- Chondrichthyes
- Order
- Squaliformes
- Family
- Dalatiidae
- Genus
- Isistius
- Species
- Isistius plutodus
- Family (common)
- Kitefin sharks
- Also known as
- Bigtooth cookiecutter shark, Longtooth cookiecutter shark, Gulf dogfish
On this page
- How to recognise a largetooth cookiecutter shark
- How big is the largetooth cookiecutter shark?
- Where largetooth cookiecutter sharks live
- What largetooth cookiecutter sharks eat and how they bite
- Behaviour, light and adaptations
- Reproduction and lifespan
- Is the largetooth cookiecutter shark dangerous?
- Conservation status
- Similar species and close relatives
- Frequently asked questions
- References
How to recognise a largetooth cookiecutter shark
The body is a smooth brown cylinder, tapering only slightly at either end, with no ridges, no keels and no fin spines. There is no anal fin, and the two dorsal fins are tiny, spineless and set so far back that they sit above and just behind the equally small pelvic fins. The tail is short and broad, its upper lobe about twice the length of the lower, with a distinct notch near the tip. The pectoral fins are small and rounded and are placed high on the body immediately behind the last of the five small gill slits.
The head is the giveaway. It is short and abruptly blunt, the eyes are large, oval and angled forward to give genuine binocular overlap, and the mouth is a narrow transverse slit surrounded by thick fleshy lips built to form a seal against another animal's skin.
Inside that mouth is the character the species is named for. There are about 29 rows of small, smooth, inward-angled teeth in the upper jaw and only 19 rows below, and the lower teeth are enormous: broad, triangular, sharp-edged and, measured against body size, the largest teeth carried by any living shark. Underneath, the belly bears light-producing photophores, though many specimens lack the sharply marked dark collar around the throat that the common cookiecutter shark wears. Between the two species, tooth counts and jaw strength are the reliable separators, not colour.
How big is the largetooth cookiecutter shark?
Very small. The largest specimen ever measured is a mature female of 42.3 cm (about 17 in), and that is the figure behind every maximum you will see quoted. Most examined animals are shorter. This shark would fit comfortably along a forearm, and it weighs a few hundred grams at most; no weight has ever been published, because the handful of specimens that exist have been preserved for museums rather than weighed on deck.
The disproportion is what matters. A shark of 40 cm carries a lower jaw whose teeth, scaled to the body, exceed those of a six-metre great white. Nothing else in the shark world is built this way, and it is the reason a fish this small can take a piece out of a marlin or a whale.
Size at birth, size at maturity and growth rate are all unrecorded. Mature females have been identified at just over 40 cm and immature individuals below that, which brackets maturity somewhere in the high thirties, but with so few specimens the bracket is wide. There is no growth curve for the species, and none is possible until many more animals are collected. The size bar below sets the 42 cm maximum against a diver, which is the fairest way to grasp the scale of the animal responsible for those wounds.
Where largetooth cookiecutter sharks live
The known records are few and scattered right across the warm oceans, which is typical of a small, fast-moving midwater animal that almost nothing catches. In the Atlantic, specimens have come from the Gulf of Mexico off Alabama, from off Bahia in Brazil, from the Azores in Portuguese waters, and from off Western Sahara. In the Pacific they have been taken off Okinawa in Japan and off New South Wales in Australia. Nothing connects those points except deep, warm, open water, so the real distribution is almost certainly circumglobal in tropical and warm temperate seas, with the map reflecting where research vessels happened to fish.
The usual depth band is 60 to 200 m over continental shelves, slopes and trenches, which is shallower than most people expect for a deep-sea shark. It is also the band where the prey is, because tuna, billfish, squid and cetaceans all use it. There is a single record from far deeper, near 6,440 m, which is the source of the claim sometimes repeated that this shark lives four miles down; one capture is not a depth range, and the honest statement is that the species is normally an upper-slope and midwater animal that may descend far further on occasion.
A fuller account of the deep fauna where the type specimen came from is on our sharks of the Gulf of Mexico page.
What largetooth cookiecutter sharks eat and how they bite
This shark is an ectoparasite. It does not kill its prey and it does not eat whole animals; it removes a piece and leaves. The victims recorded, from the wounds they carry, include tuna, billfish, dolphinfish, other sharks, squid, seals, dolphins and large whales, along with anything else big enough to be worth biting.
The mechanism is precise. The shark closes with the flank of a much larger animal, seals its fleshy lips against the skin to form a suction cup, sinks the small upper teeth in as anchors, then swings the huge lower teeth through the flesh and rotates its whole body. What comes away is a conical plug, and what is left behind is a clean, round, crater-shaped wound with parallel grooves scored down its walls by the individual teeth. The name cookiecutter comes from precisely that shape.
The largetooth species leaves a bigger, deeper and more elongated wound than the common cookiecutter, because its jaw is stronger and its teeth fewer and larger. Work on stranded and photographed cetaceans off Brazil has attributed the large majority of cookiecutter wounds in that region to this species rather than to its commoner relative, which suggests it is far less rare than the specimen count implies. The wounds themselves are rarely fatal to a big animal, though repeated bites on the same fish can be serious, and claims that the shark regularly kills its targets go well beyond the evidence.
Behaviour, light and adaptations
Nothing about this shark's build suggests speed. The fins are small and set far back, the muscle mass is modest, and the tail is short. It cannot chase down a tuna, and it does not try to. Instead it hangs almost motionless in the water column, held there by a very large liver packed with low-density oil that occupies much of the body cavity and makes the animal close to neutrally buoyant. Hunting is a matter of waiting for something big to come within a metre and then striking once.
The ambush is probably helped by light. The belly carries bioluminescent photophores, which in the related common cookiecutter produce a soft green glow that erases the shark's silhouette against the faint light from above. In that species a dark collar around the throat stays unlit, and the leading hypothesis is that the dark patch reads to a predator below as a small fish against a glowing background, luring it into range. Whether the largetooth species uses the same trick is untested, because several specimens lack a well-marked collar and none has been observed alive.
The forward-set eyes point to the same lifestyle. Binocular overlap gives depth perception, which matters enormously for an animal that gets a single chance to place a bite on a moving flank. Almost everything else about its behaviour, whether it migrates vertically at night as its relative does, whether it aggregates, how often it feeds, remains unrecorded; see our shark anatomy page for the structures involved.
Reproduction and lifespan
The reproduction of the largetooth cookiecutter shark has never been described. No pregnant female has been dissected and reported, no embryo has been measured, and no litter has been counted. That is a direct consequence of how few specimens exist.
The mode is inferred from the family. All kitefin sharks and their relatives are ovoviviparous, or more exactly yolk-sac viviparous: the eggs stay inside the mother in thin membranes, the embryos live on their yolk with no placental connection, and the young are born fully formed and independent. There is no egg case, no nursery and no parental care. In the common cookiecutter, the only member of the genus with any reproductive data at all, litters run to about six to twelve pups. Whether the largetooth species matches that is unknown.
Maturity can be bracketed roughly. Females identified as mature have measured just over 40 cm, and smaller specimens have been immature, so the transition happens somewhere in the high thirties of centimetres. Males are too poorly represented to say anything useful.
Lifespan is entirely unknown. No vertebral ageing study exists for this species, and none is likely soon. Small squaliform sharks that have been aged live for one to three decades, and a parasitic feeder with no great energy demands would sit within that range, but that is reasoning by analogy rather than measurement; our page on how long sharks live explains why deep-water species are so hard to age.
Is the largetooth cookiecutter shark dangerous?
The SharkSider database holds no incident attributed to this species, and no bite on a person has ever been assigned to it anywhere. The few records in the database that name a cookiecutter shark do not identify which of the two species was involved, and they are held on the cookiecutter shark page rather than here.
That said, the genus is one of the very few that can bite a living person without the encounter being a predatory mistake. Cookiecutter bites on open-water swimmers and on triathletes crossing Hawaiian channels at night are documented, and they produce the same neat crater a tuna carries. They are painful and slow to heal but not life-threatening, and every known case involves a swimmer far offshore in deep water at night, which is an extremely rare situation.
For the largetooth species specifically there is no record at all, and its scarcity in collections makes an encounter vanishingly unlikely. The practical risk to an ordinary swimmer, diver or surfer is zero. The realistic contact is industrial: these sharks turn up occasionally in midwater trawls and on longlines, and they damage the catch and the gear rather than the crew.
The SharkSider database has no incident attributed to this species. The database draws on the International Shark Attack File, the Global Shark Attack File and verified local reports, and is updated weekly.
Conservation status
The IUCN assessed the largetooth cookiecutter shark as Least Concern in 2024. The reasoning is not that the population is known to be healthy, because it is not known at all; it is that the shark is widely distributed across the warm oceans, has no commercial value, and is not targeted by any fishery.
Such contact as there is comes through bycatch in pelagic longlines and midwater trawls, and it is incidental and small. Nothing about it attracts fishing effort: too small to sell, too rare to accumulate, and dispersed in open water rather than in workable concentrations.
The genuine problem is information. Fewer than a few dozen specimens have been examined since the species was described in 1964, there is no population estimate, no trend, and no biological study of growth or reproduction. Evidence from cetacean wounds off Brazil suggests the animal is a great deal commoner than the specimen record implies, which if true is reassuring, but it also shows how little the collections tell us. A Least Concern rating founded on the absence of a known threat is a different thing from one founded on evidence of stability, and our explainer on the IUCN Red List sets out that distinction. No cookiecutter shark is listed on any CITES appendix.
Similar species and close relatives
The only shark that seriously resembles this one is its own congener, the cookiecutter shark, Isistius brasiliensis, which is commoner, slightly longer, carries a sharply defined dark collar and has more and smaller lower teeth set in a weaker jaw. Where both occur, the wound is often a better clue than the shark: a largetooth bite is deeper and more elongated. The two also differ in fin placement, with the dorsal fins set further back in the largetooth species.
The wider family is the kitefin sharks, small to medium squaliforms of deep water. The kitefin shark is the giant of the group at around 1.6 m and the largest bioluminescent vertebrate known. At the other end sit the dwarfs: the pygmy shark and the spined pygmy shark, among the smallest sharks in the world, and the smalleye pygmy shark, all of them glowing, all of them midwater, but none of them parasitic. The rarely seen taillight shark belongs to the same family and carries a luminous gland at the base of its tail.
None of these relatives feeds the way the cookiecutters do. Parasitic flesh-taking evolved once in this group, and the largetooth species pushed it furthest.
Cookiecutter Sharkspecies profile- Kitefin Sharkspecies profile
Pygmy Sharkspecies profile- Spined Pygmy Sharkspecies profile
- Smalleye Pygmy Sharkspecies profile
- Taillight Sharkspecies profile
Frequently asked questions
How big is a largetooth cookiecutter shark?
The largest specimen ever measured is a mature female of 42.3 cm, about 17 inches, and most examined animals are smaller. No weight has been published, but the shark would weigh a few hundred grams at most. Size at birth and growth rate are unknown, and maturity appears to fall somewhere in the high thirties of centimetres.
Why is it called the largetooth cookiecutter shark?
For its lower teeth, which relative to body size are the largest of any living shark. It has only about 19 rows below, against 29 above, and each lower tooth is broad, triangular and sharp-edged. The cookiecutter part of the name comes from the neat round crater its bite leaves in the flesh of larger animals.
What does the largetooth cookiecutter shark eat?
It eats pieces of other animals. It seals its lips against the flank of a tuna, billfish, squid, shark, seal, dolphin or whale, anchors with the small upper teeth, swings the big lower teeth through the flesh and rotates, removing a conical plug. The victim survives; the shark takes only what fits in its mouth.
Where does the largetooth cookiecutter shark live?
Records are scattered across the warm oceans: the Gulf of Mexico off Alabama, off Bahia in Brazil, the Azores, Western Sahara, Okinawa in Japan and New South Wales in Australia. It normally occupies the 60 to 200 m band over shelves and slopes, and the distribution is probably circumglobal in tropical and warm temperate seas.
How deep does the largetooth cookiecutter shark go?
Usually between 60 and 200 m, which is shallower than most deep-sea sharks, because that is where its prey swims. A single capture near 6,440 m is the source of the widely repeated claim that it lives four miles down. One record is not a depth range, and the species should be thought of as a midwater and upper-slope animal.
Is the largetooth cookiecutter shark dangerous to humans?
There is no recorded bite by this species on a person anywhere, and none in the SharkSider database. Its commoner relative has bitten long-distance swimmers crossing deep water at night, producing a painful but survivable crater wound. For ordinary swimming, diving or surfing the risk from either cookiecutter is effectively zero.
How does the largetooth cookiecutter shark reproduce?
Nobody knows. No pregnant female has ever been described, no embryo measured and no litter counted. Every member of the family is yolk-sac viviparous, meaning the young develop inside the mother on yolk alone with no placenta and are born fully formed, so this species almost certainly does the same. Litter size remains unrecorded.
How many largetooth cookiecutter sharks have been found?
Only a small number, on the order of a few dozen since the species was described from a Gulf of Mexico specimen in 1964. That scarcity may be an artefact of sampling rather than of the animal. Studies of bite wounds on cetaceans off Brazil attribute most of them to this species, which suggests it is considerably commoner than collections imply.
Is the largetooth cookiecutter shark endangered?
The IUCN listed it as Least Concern in 2024. It is widely distributed, has no commercial value and is not targeted by any fishery, appearing only as occasional bycatch on longlines and in midwater trawls. There is no population estimate or trend, so the rating reflects the absence of a known threat rather than measured stability.
How is it different from the common cookiecutter shark?
The largetooth has fewer and much larger lower teeth, about 19 rows against 25 to 31, set in a stronger jaw, and its dorsal fins sit further back. Many specimens lack the sharp dark collar the common cookiecutter wears around the throat. Its bite wounds are correspondingly deeper and more elongated.
References
A small team focused on researching sharks and making marine biology easy to understand. Every page is reviewed against current species records and the SharkSider attack database, and updated when new incidents or research appear.
Published October 14, 2022 · Last updated September 22, 2026 · No incident attributed to this species in the SharkSider attack database, which is updated weekly.
