Hammerhead Shark

Lore & Background

Because sharks do not have mineralized bones and rarely fossilize, only their teeth are commonly found as fossils. Their closest relatives are the requiem sharks (Carcharinidae). Based on a recent combined molecular and paleontological study, the ancestor of the hammerheads probably lived in the Cretaceous or Paleocene. Definitive fossils of the family date back to the Eocene. Prior DNA studies had estimated the family to have arisen in the Miocene, about 20 million years ago. Using mitochondrial DNA, a phylogenetic tree of the hammerhead sharks showed the winghead shark as sister to the rest of the hammerhead sharks. As the winghead shark has proportionately the largest "hammer" of the hammerhead sharks, this suggests that the first ancestral hammerhead sharks also had large hammers.

In Their Own Story

The water turned a deep, inky blue as the sun dipped below the horizon. A single shadow detached itself from the massive school hovering near the reef wall. The Great Hammerhead moved with a slow, deliberate grace, its wide head slicing through the current like a submarine prow. Beneath it, the sandy bottom was a landscape of secrets, but the shark needed no eyes to see them. Its cephalofoil swept side to side, reading the invisible electric whispers of a stingray buried inches deep in the silt. With a sudden burst of power, the shark pivoted, its tail driving it downward. The sand erupted as jaws clamped shut on hidden prey, the school above swirling in a silent, synchronized dance before fading back into the twilight. Alone now, the predator began its night patrol, guided by currents and electric signals rather than light.

Reader's Guide

Hammerhead shark species vary in length and weight. The largest species, the great hammerhead, has an average length of 13.1 feet (4.0 m) and weight of 500 pounds (230 kg). The smallest species, the bonnethead shark, can reach 5 feet (1.5 m) in length and 24 pounds (10.8 kg) in weight. They are usually light gray and have a greenish tint. Their bellies are white. Their heads have lateral projections that give them a hammer-like shape. Hammerheads have disproportionately small mouths compared to other shark species. Some species are also known to form schools. In the evening, like most other sharks, they become solitary hunters. Hammerheads can be found in warm, tropical waters, but during the summer, they begin a mass migration period in search of colder waters. The hammer-like shape of the head may have evolved at least in part to enhance the animal's vision. The positioning of the eyes allows 360° of vision in the vertical plane. They also have an increased binocular vision and depth of visual field. The shape of the head was previously thought to help the shark find food, aiding in close-quarters maneuverability, and allowing sharp turning movement without losing stability. The unusual structure of its vertebrae, though, has been found to be instrumental in making the turns correctly. From what is known about the winghead shark, the shape of the hammerhead apparently has to do with an evolved sensory function. Like all sharks, hammerheads have electroreceptory sensory pores called ampullae of Lorenzini. By distributing the receptors over a wider area, hammerheads can sweep for prey more effectively. Reproduction occurs only once a year for hammerhead sharks, and usually occurs with the male shark biting the female shark violently until she agrees to mate with him. The hammerhead sharks exhibit a viviparous mode of reproduction with females giving birth to live young. Fertilization is internal. The developing embryos are at first sustained by a yolk sac. When the supply of yolk is exhausted, the depleted yolk sac transforms into a structure analogous to a mammalian placenta (called a "yolk sac placenta" or "pseudoplacenta"), through which the mother delivers sustenance until birth. Once the baby sharks are born, they are not taken care of by the parents in any way. Usually, a litter consists of 12 to 15 pups, except for the great hammerhead, which gives bi

Did You Know?

• The hammerhead's cephalofoil gives the shark superior binocular vision and depth perception, as well as increased surface area for electroreceptors.
• The smallest hammerhead species, the bonnethead shark, can reach 5 feet in length and 24 pounds in weight.
• The great hammerhead occasionally engages in cannibalism, eating other hammerhead sharks, including mothers consuming their own young.
• In 2007, the bonnethead shark was found to be capable of asexual reproduction via automictic parthenogenesis, the first shark known to do this.
• Bonnetheads have been found to feed on seagrass, making them potentially omnivorous.

Production Challenges and Scientific Discovery

Creating this groundbreaking documentary required an unprecedented five-year commitment involving nearly two hundred distinct filming locations across the globe. The production team faced immense difficulties because the vast majority of the ocean environment remained a mystery to science at the time. To overcome these obstacles, producers collaborated with marine scientists worldwide and utilized state-of-the-art equipment to capture behaviors never before witnessed or recorded. A notable example involved tracking blue whales; after tagging them with temporary radio transmitters, camera crews spent three years on standby in microlights until they could locate the migrating giants in the Gulf of California. The open ocean proved particularly elusive, consuming over four hundred days of often unsuccessful filming trips. However, persistence paid off when a school of spinner dolphins led the crew to tuna, and frigatebirds guided them to sailfish near Mexico. In South Africa, two seasons were dedicated to capturing the annual sardine run, while deep-sea exploration required special submersibles to dive over a mile into the San Diego trench to observe scavengers feeding on a whale carcass.

Critical Acclaim and Cultural Impact

Premiering in September 2001 as a co-production between the BBC Natural History Unit and Discovery Channel, this series was celebrated as the first comprehensive look at the natural history of the world's oceans. Narrated by the legendary David Attenborough, the eight-episode run achieved massive viewership, with over twelve million people tuning in for the initial broadcast on BBC One and regularly securing an audience share exceeding thirty percent. The show's artistic excellence was recognized globally, earning numerous Emmy and BAFTA TV awards specifically for its innovative cinematography and musical score composed by George Fenton. The success of this project paved the way for future landmark series like *Planet Earth* and eventually led to the highly anticipated sequel, *Blue Planet II*, which aired fifteen years later.

Theatrical Releases and Live Experiences

The visual spectacle of the documentary was successfully adapted into various formats beyond standard television broadcasting. This immersive experience featured spectacular sequences projected onto an eighteen-meter-wide screen standing three stories high. The performances were accompanied by George Fenton conducting the Manchester Camerata Orchestra, with critically acclaimed shows held in major cities including London, Cardiff, and Wembley Arena. These live events allowed audiences to witness the ocean's majesty on a grand scale, often introduced by special guests.

Home Media and Educational Resources

To extend the reach of this marine masterpiece, extensive home media collections were released globally, offering fans deep dives into the production process. The initial release was a three-disc DVD set in late 2001, which later evolved into expanded Special Editions containing additional documentaries such as *Deep Trouble* and *Dive to Shark Volcano*. Complementing these visual releases were comprehensive books published by BBC Worldwide and Dorling Kindersley. Written by Andrew Byatt, Alastair Fothergill, and Martha Holmes, these volumes served as detailed companions to the series, featuring a foreword by Attenborough. These resources ensured that the educational value of the documentary remained accessible long after its initial broadcast, preserving the knowledge gained from the five-year filming expedition for future generations.