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.
|Dwarf sperm whale, Kogia sima|
A number of genera are extinct.
There is some amount of uncertainty over if Kogiidae belong in the sperm whale family. Research still suggests a close relationship between Kogiidae and sperm whales using mitochondrial DNA, which supports Kogiidae as part of the sperm whale family. Other phylogenetic research raises further questions over a potential relationship between kogiids and Ziphiidae. Other questions exist regarding the high relatedness in mitochondrial DNA between Platanista and kogiids. Fossil evidence is limited for this family, which potentially limits an understanding of their relationship to other extant cetaceans.
Researchers have proposed that K. sima may represent at least two genetically unique species, and further genetic research is needed to determine the real number of extant species of Kogiidae.
- Infraorder Cetacea
- Parvorder Odontoceti toothed whales
- Superfamily Physeteroidea
- Family Kogiidae
- Genus Kogia
- Genus Aprixokogia †
- Genus Kogiopsis †
- Genus Nanokogia †
- Genus Pliokogia †
- Genus Praekogia †
- Genus Scaphokogia †
- Genus Thalassocetus †
- Family Kogiidae
- Superfamily Physeteroidea
- Parvorder Odontoceti toothed whales
Kogiid skulls are characterized by a very short rostrum, the smallest among extant cetaceans, as well as high levels of asymmetry, which is expected among odontocetes. Kogiid skulls have the most blunt mandible among extant cetaceans as well. Extant kogiidae also show relatively high encephalization quotient, the ratio between observed brain size and expected brain size. The pygmy sperm whale has an EQ of 1.78, while the dwarf sperm whale's EQ is 1.63. Kogiidae do possess spermaceti in their head like sperm whales. However, kogiid spermaceti is unique as the whales are able to control its temperature. Kogiidae are also homodonts, showing teeth all of the same size and shape.
Two fossilized species of Kogia sp. were shown to exhibit sympatry, similar to the two modern members of Kogia, which researchers suggested shows that this behavior has been part of Kogiidae for at least 3 million years.
Behavior and feedingEdit
Kogiidae are deep diving whales, believed to dive up to depths of 500m. Kogiids feed using a technique known as suction feeding, and their diet primarily consists of squid. Pygmy sperm whales are able to eat larger prey than dwarf sperm whales, although their diet as a whole is relatively similar. They have also been observed using echolocation to find their prey.
Most observations of Kogia have come from individuals tangled in fishing line or stranded individuals. There is a commercial fishery for K. breviceps in parts of southeast Asia and the Lesser Antilles. Both species of extant kogiidae have also been observed stranded with plastics blocking their intestines.
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