Melon (cetacean)

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Mass of fat found in all toothed whales

title: "Melon (cetacean)" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["cetacean-anatomy", "whale-sounds"] description: "Mass of fat found in all toothed whales" topic_path: "science/biology" source: "https://en.wikipedia.org/wiki/Melon_(cetacean)" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Mass of fat found in all toothed whales ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/1/1a/Dolphin_head_bisected.jpg" caption="The bisected head of a dolphin: The melon is just above the upper jaw."] ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/b/ba/Cetacean_melons.jpg" caption="Three-dimensional models of various odontocete melons based on CT scans"] ::

The melon is a mass of adipose tissue found in the foreheads of all toothed whales. 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.

Description

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. It was once hypothesized that the melon had functions in deep diving and buoyancy, but these ideas are no longer considered plausible by cetologists.

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.

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" (melon).

The melon is not homologous to the spermaceti organ. Research on the expression of genes such as that for the protein MYH16 show it originates from the masseter muscle.

Composition

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. 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. 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).

Pilot whales

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.

Pygmy sperm whale

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.

::figure[src="https://upload.wikimedia.org/wikipedia/commons/5/52/Kogia_breviceps_sagittal_+_coronal.svg"] ::

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.

::data[format=table title="Melon composition in ''K. breviceps''{{cite journal|last1=Karol|first1=R.|last2=Litchfield|first2=C.|last3=Caldwell|first3=D. K.|last4=Caldwell|first4=M. C.|title=Compositional topography of melon and spermaceti organ lipids in the pygmy sperm whale ''Kogia breviceps'': Implications for echolocation|journal=Marine Biology|date=1978|volume=47|issue=2|pages=115–123|doi=10.1007/BF00395632|bibcode=1978MarBi..47..115K |s2cid=84443478 }}"] | Outer melon | Inner melon | Spermaceti organ | Lipid content (weight) | Lipid composition | Wax esters | Triglycerides | Average number of carbons | Wax esters | Triglycerides | |---|---|---|---|---|---|---|---|---|---| | 15–91% | 74–94% | 92–96% | | | | | | | | | 8–46% | 40–90% | 84–99% | | | | | | | | | 54–92% | 10–69% | 1–16% | | | | | | | | | 32–35 | 29–32 | 28–29 | | | | | | | | | 47–51 | 41–46 | 45 | | | | | | | | ::

Sperm whale

Sperm whales have two large oil-filled sacs, stacked one on top of the other: the dorsal spermaceti organ or spermaceti case and the junk, named because whalers dismissed it as worthless for extracting sperm oil. The junk originated from the odontocete melon. It contains compartments of waxy oils separated by walls of connective tissue. Together, the spermaceti organ and the junk add directionality and amplitude to biosonar clicks.

Beluga whale

The melon of the beluga whale is unique in that the whale can change the melon's shape at will. These changes in shape probably change the size, shape, direction, and frequency composition of the echolocation beam.

References

References

  1. Cranford, Ted W.. (June 1996). "Functional morphology and homology in the odontocete nasal complex: Implications for sound generation". Journal of Morphology.
  2. Harper, C.J.. (July 2008). "Morphology of the melon and its tendinous connections to the facial muscles in bottlenose dolphins (Tursiops truncatus)". Journal of Morphology.
  3. Cranford, Ted W.. (October 1999). "The sperm whale's nose: Sexual selection on a grand scale?". Marine Mammal Science.
  4. [https://books.google.com/books?id=OwF05MfTagsC&pg=PA107 ''Marine Mammal Biology: An Evolutionary Approach'']. pg 153
  5. (April 2008). "Anatomic Geometry of Sound Transmission and Reception in Cuvier's Beaked Whale (''Ziphius cavirostris'')". The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology.
  6. (2024). "A tradeoff evolution between acoustic fat bodies and skull muscles in toothed whales". Gene.
  7. (September 1971). "Isovaleroyl triglycerides from the blubber and melon oils of the beluga whale (''Delphinapterus leucas'')". Lipids.
  8. (April 1975). "Comparative lipid patterns in acoustical and non-acoustical fatty tissues of dolphins, porpoises and toothed whales". Comparative Biochemistry and Physiology Part B: Comparative Biochemistry.
  9. (December 1973). "Heterogeneity of lipid composition within the cephalic melon tissue of the pilot whale (''Globicephala melaena'')". Biochimica et Biophysica Acta (BBA) - Lipids and Lipid Metabolism.
  10. (1978). "Compositional topography of melon and spermaceti organ lipids in the pygmy sperm whale ''Kogia breviceps'': Implications for echolocation". Marine Biology.
  11. Clarke, Malcolm R.. (February 1978). "Structure and Proportions of the Spermaceti Organ in the Sperm Whale". Journal of the Marine Biological Association of the United Kingdom.
  12. (1990). "Evolution of the Nasal Anatomy of Cetaceans". Springer US.
  13. (2000-01-01). "Sperm whale clicks: Directionality and source level revisited". The Journal of the Acoustical Society of America.
  14. Møhl, Bertel. (2001-06-01). "Sound transmission in the nose of the sperm whale Physeter catodon. A post mortem study". Journal of Comparative Physiology A.
  15. (31 May 2010). "Beluga Whale wiggling its Melon at Vancouver Aquarium". YouTube.

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