On behalf of my colleagues (Haruka Ito and Keiichi Ueda) I am pleased to announce the publication of our new article in the Journal of Morphology on whale feeding and TMJ motion: https://onlinelibrary.wiley.com/journal/10974687
Werth, A.J., H. Ito, and K. Ueda. Multiaxial movements at the minke whale temporomandibular joint. Journal of Morphology, 2020;1�C11. https://doi.org/10.1002/ jmor.21107 Abstract: Mandibular mobility accompanying gape change in Northern and Antarctic minke whales was investigated by manipulating jaws of carcasses, recording jaw movements via digital instruments (inclinometers, accelerometers, and goniometers), and examining osteological and soft tissue movements via computed tomography (CT)�\scans. We investigated longitudinal (α) rotation of the mandible and mediolateral displacement at the symphysis (Ω1) and temporomandibular joint (Ω2) as the mouth opened (Δ). Results indicated three phases of jaw opening. In the first phase, as gape increased from zero to 8°, there was slight (<1°) α and Ω rotation. As gape increased between 20 and 30°, the mandibles rotated slightly laterally (Mean 3°), the posterior condyles were slightly medially displaced (Mean 4°), and the anterior ends at the symphysis were laterally displaced (Mean 3°). In the third phase of jaw opening, from 30° to full (≥90°) gape, these motions reversed: mandibles rotated medially (Mean 29°), condyles were laterally displaced (Mean 14°), and symphyseal ends were medially displaced (Mean 1°). Movements were observed during jaw manipulation and analyzed with CT�\images that confirmed quantitative inclinometer/accelerometer data, including the unstable intermediate (Phase 2) position. Together these shifting movements maintain a constant distance for adductor muscles stretched between the skull's temporal fossa and mandible's coronoid process. Mandibular rotation enlarges the buccal cavity's volume as much as 36%, likely to improve prey capture in rorqual lunge feeding; it may strengthen and stabilize jaw opening or closure, perhaps via a simple locking or unlocking mechanism. Rotated lips may brace baleen racks during filtration. Mandibular movements may serve a proprioceptive mechanosensory function, perhaps via the symphyseal organ, to guide prey engulfment and water expulsion for filtration. Best regards, Alex _______________________________ Alexander J. Werth, Ph.D. Trinkle Professor of Biology Hampden-Sydney College Box 162, Hampden-Sydney, VA 23943 434-223-6326, fax 434-223-6374 http://www.hsc.edu/alex-werth
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