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Pygmy sperm whale
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==Echolocation== Like all toothed whales, the pygmy sperm whale hunts prey by [[Animal echolocation|echolocation]]. Sound produced for echolocation by many odontocetes come in the form of high-frequency clicks.<ref name="Marten2000" /> The frequencies it uses are mostly ultrasonic,<ref name="Karoletal978"/> peaking around 125 kHz.<ref name=Marten2000/> The clicks from their echolocation has been recorded to last an average of 600 microseconds. When closing in on prey, the click repetition rate starts at 20 Hz and then begins to rise when nearing the target.<ref name="Marten2000" /> The pulse sounds that pygmy sperm whales make for echolocation are generated primarily from the ''museau de singe'' or monkey's muzzle, which is an anatomical structure located within the whale's skull that produces sound when air passes through its lips.<ref name="Karoletal978" /> The sound from the ''museau de singe'' is transferred to the attached cone of the spermaceti organ. Unique from other odontocetes, the spermaceti organ contacts the posterior of the whale's melon.<ref name="Karoletal978" /> Fat from the core of the spermaceti organ helps direct sonic energy from the ''museau de singe'' to the melon.<ref name="Karoletal978" /> The melon acts as a sonic magnifier and gives directionality to sound pulses, making echolocation more efficient. Fat on the interior of the melon has a lower molecular weight lipid than the surrounding outer melon.<ref name="Karoletal978" /> Since the sound waves move from a lower velocity material to a higher one during sound production, the sound undergoes inward refraction and becomes increasingly focused. Variation in fat density within the melon ultimately contributes to the production of highly directional, ultrasonic sound beams in front of the melon. The combined melon and spermaceti organ system cooperate to focus echolocative sounds.{{fact|date=May 2024}} Like in most odontocetes, the known echoreception apparatus used by the pygmy sperm whale is linked to the fat-filled lower mandibles within the skull.<ref name="Karoletal978" /> However, compositional topography of the pygmy sperm whale's skull indicates abnormally large fatty jowls surrounding the mandibles, suggesting a more intricate echoreception apparatus.<ref name="Karoletal978" /> Additionally, an unusual cushion structure, of porous and spongy texture, found behind the ''museau de singe'' has been hypothesized of being a possible "pressure receptor".<ref name="Karoletal978" /> The positioning of this cushion structure in close proximity to the largest cavities closest to the ''museau de singe'' may suggest that it is a sound absorber used for echoreception.{{fact|date=May 2024}}
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