The melon is a mass of adipose tissue found in the foreheads of all toothed whales. [1] [2] It focuses and modulates the animal's vocalizations and acts as a sound lens. It is thus a key organ involved in communication and echolocation.
The melon is a mass of adipose tissue found in the foreheads of all toothed whales. [1] [2] It focuses and modulates the animal's vocalizations and acts as a sound lens. It is thus a key organ involved in communication and echolocation.
The melon is structurally part of the nasal apparatus and comprises most of the mass tissue between the blowhole and the tip of the snout. The function of the melon is not completely understood, but scientists believe it is a bioacoustic component, providing a means of focusing sounds used in echolocation and creating a similarity between characteristics of its tissue and the surrounding water so that acoustic energy can flow out of the head and into the environment with the least loss of energy. In the past, some scientists believed that the melon had functions in deep diving and buoyancy, but these ideas have been discounted over the last 40 years, so are no longer considered valid by cetologists. [3]
The varying composition of the melon creates a sound velocity gradient that refracts sound directionally. Sounds also bounce off the skull and air sacs that surround the melon. [4]
Melon size is unrelated to maximum dive depth in toothed whales. The particular characteristics of the melon probably have more to do with odontocete phylogeny, the taxonomic relationships over evolutionary time. In some species, melons are more specialized than in others. The sperm whale has the largest nose of any animal in the world. The bulk of that nose is composed of two large, fatty structures, the spermaceti organ and the "junk". The junk is structurally the same as the melon (homologous to it).
The melon is not homologous to the spermaceti organ. [1] [5] Research on the expression of genes such as that for the protein MYH16 show it originates from the masseter muscle. [6]
The melon is a mixture of triglycerides and wax esters. The exact composition varies throughout the melon. Typically, the inner core of the melon has a higher wax content than the outer parts and conducts sound more slowly. This gradient refracts sound and focuses it like a lens.
The lipids in the melon cannot be digested by the animal, as they are metabolically toxic. A starving dolphin has a robust melon even if the rest of its body is emaciated. [1] The lipids in the melon tend to be of lower molecular weight and more saturated than the blubber.
The melons of the Delphinidae (dolphins) and Physeteroidea (sperm whales) have a significant amount of wax ester, whereas those of the Phocoenidae (porpoises) and Monodontidae (narwhals and beluga whales) contain little or no wax. [7] The speed of sound in the melon is lowest in the Delphinidae, Phocoenidae, and Monodontidae, intermediate in the Ziphiidae (beaked whales), and highest in the Physeteridae and Platanistidae (South Asian river dolphins). [8]
The melon of pilot whales (Globicephala) is a mixture of wax esters and triglycerides. The inner core of the melon is about 33% wax esters, while the outer layer is about 5% wax esters. Most of the fats are saturated. [9]
In the pygmy sperm whale (Kogia breviceps), the melon consists of an outer layer and an inner core, which has a generally larger proportion of wax esters than the outer layer. [10]
Behind the melon is a cornucopia-shaped organ that many scientists refer to as the "spermaceti organ". This organ is different in form and composition from the spermaceti organ of the sperm whale.
| Outer melon | Inner melon | Spermaceti organ | ||
|---|---|---|---|---|
| Lipid content (weight) | 15–91% | 74–94% | 92–96% | |
| Lipid composition | Wax esters | 8–46% | 40–90% | 84–99% |
| Triglycerides | 54–92% | 10–69% | 1–16% | |
| Average number of carbons | Wax esters | 32–35 | 29–32 | 28–29 |
| Triglycerides | 47–51 | 41–46 | 45 | |
The analogous structure in the sperm whale is traditionally called "the junk" because whalers dismissed it as worthless for extracting sperm oil. It contains compartments of spermaceti separated by walls of cartilage.[ citation needed ]
The melon of the beluga whale is also unique in that the whale can change the melon's shape at will. [11] These changes in shape probably have the effect of changing the size, shape, direction, and frequency composition of the echolocation beam.
Cetacea is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel themselves through the water with powerful up-and-down movement of their tail which ends in a paddle-like fluke, using their flipper-shaped forelimbs to maneuver.
Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and porpoises. Dolphins and porpoises may be considered whales from a formal, cladistic perspective. Whales, dolphins and porpoises belong to the order Cetartiodactyla, which consists of even-toed ungulates. Their closest non-cetacean living relatives are the hippopotamuses, from which they and other cetaceans diverged about 54 million years ago. The two parvorders of whales, baleen whales (Mysticeti) and toothed whales (Odontoceti), are thought to have had their last common ancestor around 34 million years ago. Mysticetes include four extant (living) families: Balaenopteridae, Balaenidae, Cetotheriidae, and Eschrichtiidae. Odontocetes include the Monodontidae, Physeteridae, Kogiidae, and Ziphiidae, as well as the six families of dolphins and porpoises which are not considered whales in the informal sense.
The narwhal, is a species of toothed whale. It is a member of the family Monodontidae, and the only species in the genus Monodon. An adult narwhal is typically 3.0 to 5.5 m in length and 800 to 1,600 kg in weight. The most prominent feature of the species is an adult male's long single tusk that can be up to 3 m (9.8 ft). The narwhal has a mottled pigmentation, with blackish-brown markings over a white background. Instead of a dorsal fin, it possesses a shallow dorsal ridge. It is a social animal, and may associate in groups of up to 20 members. Carl Linnaeus scientifically described the species in 1758 in his work Systema Naturae.
The beluga whale is an Arctic and sub-Arctic cetacean. It is one of two members of the family Monodontidae, along with the narwhal, and the only member of the genus Delphinapterus. It is also known as the white whale, as it is the only cetacean to regularly occur with this colour; the sea canary, due to its high-pitched calls; and the melonhead, though that more commonly refers to the melon-headed whale, which is an oceanic dolphin.
The cetacean family Monodontidae comprises two living whale species, the narwhal and the beluga whale and at least four extinct species, known from the fossil record. Beluga and Narwhal are native to coastal regions and pack ice around the Arctic Ocean. Both species are relatively small whales, between three and five metres in length, with a forehead melon, and a short or absent snout. They do not have a true dorsal fin, but do have a narrow ridge running along the back, which is much more pronounced in the narwhal. They are highly vocal animals, communicating with a wide range of sounds. Like other whales, they also use echolocation to navigate. Belugas can be found in the far north of the Atlantic and Pacific Oceans; the distribution of narwhals is restricted to the Arctic and Atlantic Oceans.
The sperm whale or cachalot is the largest of the toothed whales and the largest toothed predator. It is the only living member of the genus Physeter and one of three extant species in the sperm whale family, along with the pygmy sperm whale and dwarf sperm whale of the genus Kogia.
Spermaceti is a waxy substance found in the head cavities of the sperm whale. Spermaceti is created in the spermaceti organ inside the whale's head. This organ may contain as much as 1,900 litres (500 US gal) of spermaceti. It has been extracted by whalers since the 17th century for human use in cosmetics, textiles, and candles.
Physeteroidea is a superfamily that includes three extant species of whales: the sperm whale, in the genus Physeter, and the pygmy sperm whale and dwarf sperm whale, in the genus Kogia. In the past, these genera have sometimes been united in a single family, the Physeteridae, with the two Kogia species in the subfamily Kogiinae; however, recent practice is to allocate the genus Kogia to its own family, the Kogiidae, leaving the Physeteridae as a monotypic family, although additional fossil representatives of both families are known.
Kogiidae is a family comprising at least two extant species of Cetacea, the pygmy and dwarf sperm whales. As their common names suggest, they somewhat resemble sperm whales, with squared heads and small lower jaws, but are much smaller in size, with much shorter skulls and more notable dorsal fins than sperm whales. Kogiids are also characterized by a "false gill slit" behind their eyes.
The toothed whales are a parvorder of cetaceans that includes dolphins, porpoises, and all other whales possessing teeth, such as the beaked whales and sperm whales. 73 species of toothed whales are described. They are one of two living groups of cetaceans, the other being the baleen whales (Mysticeti), which have baleen instead of teeth. The two groups are thought to have diverged around 34 million years ago (mya).
The pygmy sperm whale is one of two extant species in the family Kogiidae in the sperm whale superfamily. They are not often sighted at sea, and most of what is known about them comes from the examination of stranded specimens.
The spermaceti organ is an organ present in the heads of toothed whales of the family Physeteroidea, in particular the sperm whale. This organ contains a waxy liquid called spermaceti and is involved in the generation of sound.
Whales use a variety of sounds for communication and sensation. The mechanisms used to produce sound vary from one family of cetaceans to another. Marine mammals, including whales, dolphins, and porpoises, are much more dependent on sound than land mammals due to the limited effectiveness of other senses in water. Sight is less effective for marine mammals because of the way particulates in the ocean scatter light. Smell is also limited, as molecules diffuse more slowly in water than in air, which makes smelling less effective. However, the speed of sound is roughly four times greater in water than in the atmosphere at sea level. As sea mammals are so dependent on hearing to communicate and feed, environmentalists and cetologists are concerned that they are being harmed by the increased ambient noise in the world's oceans caused by ships, sonar and marine seismic surveys.
Whale oil is oil obtained from the blubber of whales. Oil from the bowhead whale was sometimes known as train-oil, which comes from the Dutch word traan.
Sperm oil is a waxy liquid obtained from sperm whales. It is a clear, yellowish liquid with a very faint odor. Sperm oil has a different composition from common whale oil, obtained from rendered blubber. Although it is traditionally called an "oil", it is technically a liquid wax. It is composed of wax esters with a small proportion of triglycerides, an ester of an unsaturated fatty acid, and a branched-chain fatty alcohol. It is a natural antioxidant and heat-transfer agent. In the late-18th and early-19th centuries, sperm oil was prized as an illuminant for its bright, odorless flame and as a lubricant for its low viscosity and stability. It was supplanted in the late 19th century by less expensive alternatives such as kerosene and petroleum-based lubricants. With the 1987 international ban on whaling, sperm oil is no longer legally sold.
Odobenocetops is an extinct genus of small toothed whale known from Chile and Peru. Its fossils are found in Miocene-aged marine strata of the Bahía Inglesa Formation and Pisco Formation. Two species of Odobenocetops are currently recognized, O. peruvianus and the slightly younger O. leptodon.
The Cetruminantia are a clade made up of the Cetancodontamorpha and their closest living relatives, the Ruminantia.
Hexadecyl hexadecanoate, also known as cetyl palmitate, is the ester derived from hexadecanoic acid and 1-hexadecanol. This white waxy solid is the primary constituent of spermaceti, the once highly prized wax found in the skull of sperm whales. Cetyl palmitate is a component of some solid lipid nanoparticles.
Artiofabula is a clade made up of the Suina and the Cetruminantia. The clade was found in molecular phylogenetic analyses and contradicted traditional relationships based on morphological analyses.
Macroraptorial sperm whales were highly predatory whales of the sperm whale superfamily (Physeteroidea) of the Miocene epoch that hunted large marine mammals, including other whales, using their large teeth. They consist of five genera: Acrophyseter, Albicetus, Brygmophyseter, Livyatan, and Zygophyseter. All species are known by at least a skull, and are informally grouped without a family designation. They were all likely the apex predator of their habitats, comparable to the modern day killer whale, and achieved great lengths, with one species–Livyatan–measuring about 13.5–17.5 m (44–57 ft).