Cetacean tongue mobility and function: A comparative review

Abstract

Cetaceans are atypical mammals whose tongues often depart from the typical (basal) mammalian condition in structure, mobility, and function. Their tongues are dynamic, innovative multipurpose tools that include the world's largest muscular structures. These changes reflect the evolutionary history of cetaceans' secondary adaptation to a fully aquatic environment. Cetacean tongues play no role in mastication and apparently a greatly reduced role in nursing (mainly channeling milk ingestion), two hallmarks of Mammalia. Cetacean tongues are not involved in drinking, breathing, vocalizing, and other non‐feeding activities; they evidently play no or little role in taste reception. Although cetaceans do not masticate or otherwise process food, their tongues retain key roles in food ingestion, transport, securing/positioning, and swallowing, though by different means than most mammals. This is due to cetaceans' aquatic habitat, which in turn altered their anatomy (e.g., the intranarial larynx and consequent soft palate alteration). Odontocetes ingest prey via raptorial biting or tongue‐generated suction. Odontocete tongues expel water and possibly uncover benthic prey via hydraulic jetting. Mysticete tongues play crucial roles driving ram, suction, or lunge ingestion for filter feeding. The uniquely flaccid rorqual tongue, not a constant volume hydrostat (as in all other mammalian tongues), invaginates into a balloon‐like pouch to temporarily hold engulfed water. Mysticete tongues also create hydrodynamic flow regimes and hydraulic forces for baleen filtration, and possibly for cleaning baleen. Cetacean tongues lost or modified much of the mobility and function of generic mammal tongues, but took on noteworthy morphological changes by evolving to accomplish new tasks.

Dynamic filtration in baleen whales: recent discoveries and emerging trends

“…These hydrodynamic effects could also slightly diminish pressures where water enters at the anterior of the mouth, perhaps not sufficiently to generate truly notable subambient suction pressures, but at least enough to obviate an anterior compressive bow wave that might physically disperse small prey and/or warn them of an approaching whale. Flow experiments (Werth, 2004, Werth, 2013 using pressure transducers and videorecording of particles and prey (Werth, 2012) have confirmed that these limited yet real pressure effects in laboratory settings (Figure 7), and tantalizing photographs and video recordings of whales foraging at sea (Werth and Potvin, 2016;Werth and Crompton, 2023) have likewise supported conclusions of Bernoulli and Venturi effects.…”

“…In addition to laterally supporting and constraining the baleen racks, the lips may be especially important in generating and modifying flow regimes (Werth et al, 2018a;Werth et al, 2019b); their positioning should be the focus of further flow experiments and field observations. The balaenid tongue may preferentially direct flow toward either rack (Werth, 2007;Werth and Crompton, 2023); it also, without moving, sets up a flow regime that channels flow toward each rack (Potvin and Werth, 2017;. Balaenids typically swim at about 0.7-1.0 m/s when filtering prey (van der Hoop et al, 2019;.…”

“…Although rorquals normally display sleek bodies adapted for rapid locomotion (both for long migrations and predatory lunges), when they engulf a capacious mouthful of prey-laden water, they briefly assume a bloated "tadpole" shape, as the accordion-like throat pleats expand over the entire ventral region, spreading posteriorly to the umbilicus (Werth et al, 2019b). Adult rorquals have a floppy, flaccid tongue (Werth and Crompton, 2023), which invaginates into a hollow interior space, the cavum ventrale, to accommodate the massive temporary influx of water, which may involve over 100 m 3 (100,000 L; Werth, 2013). Apart from stealthy "trap feeding," in which a stationary whale at the surface holds its jaws open and waits as prey accumulate inside the mouth (McMillan et al, 2019), rorquals generally lunge via rapid forward locomotion.…”

“…The very large (up to 1m high and wide and 4+m long), firm muscular tongue of all balaenid species also channels flow, dividing it and directing it into either baleen rack (Werth, 2000;Werth and Crompton, 2023). Lambertsen et al (1989) speculated that this intraoral morphology might create a Bernoulli effect, as flow speed increases due to narrowing of the pipe-like path, and that this might further generate a Venturi effect to pull water from the center of the mouth, along the tongue, through baleen.…”

“…Although this might work, there are several potential problems. First, this overestimates the mobility and muscularity of the tongue body in adult rorquals, which, in order to invaginate and line the ventral cavity of the throat pouch during lunge engulfment (Lambertsen, 1983), resembles a floppy, flaccid waterbed more than a firm tongue akin to that of most mammals (Werth and Crompton, 2023). Second, even if the tongue were not too loose to dislodge ensnared items, prey might be pushed even deeper into the filter mat, compounding the problem.…”