AnimaliaHighest rank in taxonomy. Groups all life into domains: Animalia, Plantae, Fungi, etc.IUCN CRInternational Union for Conservation of Nature — the world authority on species extinction risk, using standardized criteria. — Critically Endangered — faces an extremely high risk of extinction in the near future.In ProgressCurrent stage of this record in the editorial review workflow. Recent Sighting
Sphyrna lewini
Scalloped Hammerhead
(Griffith & Smith, 1834)
Detailed Texts Multi-lang
The scalloped hammerhead possesses one of the most extraordinary anatomies in marine evolution. Its body is fusiform, slender, and hydrodynamic, typically olive-gray or bronze on the back, fading to a pale white belly (countershading). However, its defining feature is its massively flattened and laterally extended head, known as a cephalofoil. In this species, the front margin of the cephalofoil exhibits an unmistakable central indentation flanked by two lateral indentations, giving it a 'scalloped' or arched appearance. This structure is no mere aesthetic quirk: it functions as a hydrodynamic wing that enhances maneuverability while acting as an immense sensory antenna. By spacing the eyes and nostrils at the extremes of the cephalofoil, the shark gains exceptional 360-degree binocular vision and impeccable stereo olfactory tracking. Furthermore, the entire under-surface of this vast head is densely carpeted with thousands of ampullae of Lorenzini, electro-receptor pores that allow it to scan the seabed with pinpoint accuracy to detect the tiny electrical impulses of prey hidden beneath the sand.
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TaxonomyBiological classification ranks placing this species within the tree of life, from Kingdom down to Genus.
PhylumRank below Kingdom. Groups organisms sharing a fundamental body plan (e.g., Chordata = vertebrates and some invertebrates).Chordata
ClassRank below Phylum. Subdivides by structural traits (e.g., Mammalia, Aves, Reptilia, Insecta).Elasmobranchii
OrderRank below Class. Groups related families sharing common ancestry (e.g., Carnivora, Primates).Carcharhiniformes
FamilyRank below Order. Groups closely related genera (e.g., Felidae = cats, Canidae = dogs).Sphyrnidae
GenusRank just above Species. The first word in the two-part binomial scientific name.Sphyrna
Taxonomic AuthorityThe scientist who first formally described and published this species, followed by the year of publication.(Griffith & Smith, 1834)
Record Completeness
51%Coming soon
Ecology & StatusHow this species lives: habitat preferences, diet, behavior, population status, and role in its ecosystem.
OriginWhether the species is native (evolved here), endemic (found only here), or introduced by human activity.
Native
Population TrendDirection of change in population size over time: increasing, stable, decreasing, or unknown.
Decreasing
Breeding SeasonTime of year when this species typically reproduces or flowers.
Summer
Trophic RolePosition in the food chain: producer, herbivore, carnivore, omnivore, decomposer, or parasite.
Carnivore
Recent SightingsWhether this species has been observed in the wild in Costa Rica within recent years.
Yes
Habitat SummaryOverview of the specific ecosystems and environments where this species is found in Costa Rica. Multi-lang
It is a coastal and pelagic species with a circumglobal distribution, inhabiting warm, temperate, and tropical seas. It demonstrates a deep affinity for continental shelves, island terraces, and near-shore pelagic ecosystems. During its neonatal and juvenile stages, it relies entirely on shallow bays, turbid estuaries, and coastal mangrove forests that act as protective biological nurseries against larger predators. As adults, they undertake epic oceanic migrations to open-ocean volcanic seamounts, with Cocos Island (Costa Rica) and the Galapagos Islands (Ecuador) serving as crucial global sanctuaries where they congregate by the hundreds in cold, nutrient-rich currents.BehaviourDaily activity patterns, movement, territory use, foraging style, and seasonal behavioral changes. Multi-lang
The behavior of the scalloped hammerhead presents a fascinating dichotomy dictated by the sun. During daylight hours, they are profoundly social and gregarious creatures, congregating around volcanic vents and seamounts in gigantic schools that can exceed hundreds of individuals. In these breathtaking swimming vortexes, they communicate through subtle body contortions and head shakes, establishing hierarchies dominated by the largest females positioned in the protective center of the school. This schooling behavior provides them with a formidable collective defense and facilitates mating. However, as night falls, the imposing social structure completely dissolves. The sharks disperse in spectral silence, descending solitary and aggressive into the depths or actively combing coastal sandy bottoms, transforming into highly specialized and ruthless nocturnal predators.Social ActivitySocial structure: whether the species is solitary, paired, or colonial; hierarchy and communication. Multi-lang
Extremely gregarious during the day, forming massive hierarchical schools of hundreds of individuals in pelagic zones; strictly solitary during nocturnal hunting.Feeding GuildWhat the species eats, how it forages or hunts, and its role as a consumer in the food web. Multi-lang
Nektonic and benthic carnivore, specialized predator of elasmobranchs (rays) and cephalopods.Trophic Chain DetailsSpecific interactions in local food webs: prey species, predators, competitors, and scavengers. Multi-lang
As an avid pelagic and benthic apex predator, the scalloped hammerhead regulates mid-level ocean populations. Its menu is diverse, including squids, sardines, mackerel, and crustaceans, but its absolute specialty—for which its head acts as a master tool—is subduing benthic elasmobranchs, particularly stingrays and eagle rays. It uses the extremes of its cephalofoil to batter, pin, and physically press rays against the seabed before devouring them. On the other side of the food chain, while adults are rarely hunted naturally, young and neonatal hammerheads face a terrifying gauntlet of predation in their coastal habitats, frequently being devoured by bull sharks (Carcharhinus leucas), massive tiger sharks (Galeocerdo cuvier), and even pods of orcas.Reproductive BehaviourMating strategies, courtship displays, nesting or spawning behavior, and parental care. Multi-lang
Reproduction is placental viviparous, a highly advanced reproductive trait. Following a violent courtship where the male relentlessly bites the female's pectoral fins to submit her and achieve copulation, embryos develop in the uterus initially sustained by a yolk sac. Once depleted, the sac transforms into a direct placental connection to the mother's uterine wall, drawing nutrients directly from her bloodstream, much like in mammals. After an extensive gestation of 9 to 12 months, gravid females migrate to warm, shallow coastal estuaries and bays. There, they give birth to considerable litters ranging from 12 to over 40 pups (neonates). These pups are born with an extremely flexible cartilaginous cephalofoil folded backward, which stiffens and takes its hammer shape minutes after birth. Immediately after birth, the pups are left completely alone, relying on their own instincts to survive.Physical Measures
Length (cm)
40.0 - 430.0 cm
Weight (Grams)
500 g - 152.00 kg
Offspring per cycleTypical number of young (live births, eggs, or seeds) produced by one adult in a single reproductive event or breeding season.12 - 40
Sexual DimorphismObservable physical differences between males and females of the same species (e.g., size, coloration, features).Yes
Lifespan
Sexual MaturityAge at which the individual becomes capable of reproducing for the first time.
10 - 15 Years
Gestation / IncubationDuration from fertilization to birth (mammals) or to hatching (egg-laying species).
9 - 12
Lifespan EstimatedExpected duration of life from birth to natural death under wild conditions.
Males20 - 30 Years
Females20 - 35 Years
Sexual DimorphismPhysical differences in size, coloration, or morphology between males and females of this species.
Males Multi-lang
Adult males are noticeably smaller and lighter than females. Phenotypically, their sexual maturity is distinguished by the presence of well-developed, calcified pelvic claspers (mixopterygia), tubular extensions located at the ventral base that function as copulatory organs for internal fertilization.
Females Multi-lang
Females lack pelvic claspers and present a smooth anatomy. Evolutionarily, they exhibit highly marked sexual size dimorphism, growing to considerably larger lengths and body volumes to accommodate the internal development of massive litters of live young. Additionally, they often bear permanent bite scars on their backs resulting from aggressive courtship.
Evolutionary AdaptationsInherited traits and behaviors that improve the species' survival and reproduction in its specific environment. Multi-lang
Stereoscopic Vision and Electromagnetic Radar: The radical expansion of its hammer-shaped skull houses a highly gifted sensory network. The extreme separation of its eyes grants it an astonishing visual field that includes stereo vision, allowing it to see above and below simultaneously. Concurrently, the cephalofoil maximizes the surface area for its ampullae of Lorenzini, turning its head into a highly efficient biological metal detector capable of sensing the heartbeats of stingrays buried under centimeters of dense oceanic sediment.
Thermo-Regulated Breath-Holding Dives: Recent bio-telemetry research has revealed that when making extreme dives into frigid bathypelagic waters (exceeding 800 meters) to hunt deep-sea squid, the scalloped hammerhead effectively 'holds its breath'. It firmly shuts its mouth and gill slits to prevent freezing water from stealing precious heat from its bloodstream, thus maintaining its core body and brain temperature suitable for active hunting in lethally cold conditions.
Main ThreatsDocumented pressures reducing the population: habitat loss, hunting, disease, climate change, and invasive species. Multi-lang
Demographic Collapse due to Shark Finning and Trawl Fishing: Listed as Critically Endangered (CR) by the IUCN, this species is being annihilated on a global scale. Their tall, iconic, and fibrous dorsal and pectoral fins are among the most coveted and expensive in the illegal shark fin soup trade in Asian markets. Furthermore, their tendency to swim in large schools makes them extremely vulnerable to perishing en masse as bycatch in the miles-long gillnets and longlines of industrial pelagic fisheries.
Destruction of Nursery Habitats: The expansion of coastal infrastructure, the deforestation of mangrove ecosystems, and the severe plastic and chemical pollution of estuaries are rapidly destroying their natural nurseries, leaving neonatal sharks without safe zones to grow and develop, effectively breaking the life cycle of new generations.
Interesting FactsSurprising or notable facts that highlight what makes this species unique or ecologically important. Multi-lang
Underwater Magnetic Map: Scientists have discovered that schools of hammerhead sharks navigate the vast emptiness of the open ocean by utilizing variations in the Earth's magnetic field imprinted on the basalt of the seabed, using them as invisible geomagnetic highways that guide them unfailingly toward seamounts like the Galapagos and Cocos Islands.
Resilience to Stingray Venom: Benthic stingrays are their favorite prey. It is incredibly common to observe adult hammerhead sharks swimming with multiple huge, venomous stingray barbs deeply embedded in their jaws, faces, and even near their throats. Apparently, they have developed an extreme immunological tolerance to the venom and tissue damage caused by these weapons.