The Auditory Anatomy of the Minke Whale (Balaenoptera acutorostrata): A Potential Fatty Sound Reception Pathway in a Baleen Whale

Abstract

Cetaceans possess highly derived auditory systems adapted for underwater hearing. Odontoceti (toothed whales) are thought to receive sound through specialized fat bodies that contact the tympanoperiotic complex, the bones housing the middle and inner ears. However, sound reception pathways remain unknown in Mysticeti (baleen whales), which have very different cranial anatomies compared to odontocetes. Here, we report a potential fatty sound reception pathway in the minke whale (Balaenoptera acutorostrata), a mysticete of the balaenopterid family. The cephalic anatomy of seven minke whales was investigated using computerized tomography and magnetic resonance imaging, verified through dissections. Findings include a large, well-formed fat body lateral, dorsal, and posterior to the mandibular ramus and lateral to the tympanoperiotic complex. This fat body inserts into the tympanoperiotic complex at the lateral aperture between the tympanic and periotic bones and is in contact with the ossicles. There is also a second, smaller body of fat found within the tympanic bone, which contacts the ossicles as well. This is the first analysis of these fatty tissues' association with the auditory structures in a mysticete, providing anatomical evidence that fatty sound reception pathways may not be a unique feature of odontocete cetaceans. Anat Rec, 2012. © 2012 Wiley Periodicals, Inc.

The auditory system of the minke whale (Balaenoptera acutorostrata) : a potential fatty sound reception pathway in a mysticete cetacean

“…These "ear fats" attach to the tympano-periotic complex and contact the ossicles. Preliminary investigations of the fin whale (Balaenoptera physalus) also revealed the presence of ear fats (Yamato et al, 2012). This study compares the morphology and biochemical composition of these newly described fat bodies in minke and fin whales with the acoustic fats of several odontocete species, including the bottlenosed dolphin (Tursiops truncatus), harbor porpoise (Phocoena phocoena), beluga whale (Delphinapterus leucas), and pygmy sperm whale (Kogia breviceps).…”

“…In contrast, virtually nothing is known about hearing in mysticetes, or baleen whales. Yamato et al (2012) reported the discovery of a large, well-formed fat body which extends from the blubber region to the ears of the minke whale (Balaenoptera acutorostrata). These "ear fats" attach to the tympano-periotic complex and contact the ossicles.…”

“…The morphological data for mysticete ear fats was obtained from Yamato et al (2012), which combined CT, MRI, and dissections of minke whales to create threedimensional reconstructions of the ear fats. Although the fin whale heads and ear fats were too large to fit within the available scanner, dissections showed that fin whales also have an ear fat morphology similar to minke whales (Yamato et al, 2012).…”

“…Although the fin whale heads and ear fats were too large to fit within the available scanner, dissections showed that fin whales also have an ear fat morphology similar to minke whales (Yamato et al, 2012).…”

“…Mysticetes possess very different cranial morphologies compared to odontocetes and the types of sounds used by mysticetes and odontocetes differ greatly. However, recent investigations found well-formed fat bodies associated with the tympano-periotic complex of the minke whale (Balaenoptera acutorostrata; Yamato et al, 2012). These fat bodies were referred to as "ear fats" rather than "acoustic fats", because their function has not yet been demonstrated.…”