Kogiidae
Kogiidae is a family comprising at least two extant species of Cetacea, the pygmy (Kogia breviceps) and dwarf (K. sima) 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.[2] Kogiids are also characterized by a "false gill slit" behind their eyes.[3]
There is some amount of uncertainty over if Kogiidae belongs 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.[5] This relationship is supported by similarities of the anatomical structures in the read, responsible for sound production, in particular the presence of a spermaceti organ.[6] Other phylogenetic research raises further questions over a potential relationship between kogiids and Ziphiidae.[5] Other questions exist regarding the high relatedness in mitochondrial DNA between Platanista and kogiids.[7] Fossil evidence is limited for this family, which potentially limits an understanding of their relationship to other extant cetaceans.[8]
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.[9]
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.[8][12] 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.[8] Kogiidae do possess spermaceti in their head like sperm whales.[13] However, kogiid spermaceti is unique as the whales are able to control its temperature.[14] Kogiidae are also homodonts, showing teeth all of the same size and shape.[15]
Kogiidae possess a unique system of organs to produce sound, including a bagpipe-like structure to produce sound and an amplifying horn.[14]
Kogiidae have a modified colon which works as an "ink sac", storing liquid red feces.[16] They are able to release over three gallons of this fecal "ink" to confuse or discourage predators.[17]
