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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., (© 2023 Anatomical Society.)

Baleen whales are ecosystem sentinels of microplastic pollution. Research indicates that they likely ingest millions of anthropogenic microparticles per day when feeding. Their immense prey consumption and filter-feeding behavior put them at risk. However, the role of baleen, the oral filtering structure of mysticete whales, in this process has not been adequately addressed. Using actual baleen tissue from four whale species (fin, humpback, minke, and North Atlantic right) in flow tank experiments, we tested the capture rate of plastics of varying size, shape, and polymer type, as well as chemical residues leached by degraded plastics, all of which accumulated in the baleen filter. Expanded polystyrene foam was the most readily captured type of plastic, followed by fragments, fibers, nurdles, and spherical microbeads. Nurdle and microbead pellets were captured most readily by right whale baleen, and fragments were captured by humpback baleen. Although not all differences between polymer types were statistically significant, buoyant polymers were most often trapped by baleen. Plastics were captured by baleen sections from all regions of a full baleen rack, but were more readily captured by baleen from dorsal and posterior regions. Baleen–plastic interactions underlie various risks to whales, including filter clogging and damage, which may impede feeding. We posit that plastics pose a higher risk to some whale species due to a combination of factors, including filter porosity, diet, habitat and geographic distribution, and foraging ecology and behavior. Certain whale species in specific marine regions are of the greatest concern due to plastic abundance. It is not feasible to remove all plastic from the sea; most of what is there will continue to break into ever-smaller pieces. We suggest that higher priorities be accorded to lessening humans' dependence on plastics, restricting entry points of plastics into the ocean, and developing biodegradable alternatives. [ABSTRACT FROM AUTHOR]

Enamel microstructure of 34 species in eight odontocete families is described and categorized according to structural complexity (from no or prismless enamel to highly arranged enamel in decussating layers), then correlated with parameters of ecology, life history, and occlusal function. Overall, more complex dental structure in extant and extinct cetaceans is associated with smaller, more numerous teeth in taxa that bite or grasp smaller, harder prey with longer, narrower jaws and have more oral processing. Enamel complexity loosely correlates with mechanical properties, but measurement of compressive strength is complicated by the presence of cementum overlying or in place of crown enamel. Given the presence of Hunter-Schreger bands and other indices of high microstructural complexity in archaic cetaceans (with presumed plesiomorphic characters), the absence of complex enamel, as well as more generally of gross dental form, signals a loss of complexity in various cetacean lineages. Nonetheless, it is difficult to draw robust or reliable inferences regarding either cetacean phylogeny or dental function given the pattern of presumed loss of tooth complexity, and the confounding presence of numerous exceptions (taxa with complex teeth despite limited use, or with thin, weakly developed enamel and soft, simple teeth despite high occlusal function). Although retention of a complex feature implies its continued adaptive value, and thus selection for the underlying genetic and developmental bases for that complexity, loss of complexity can simply follow absence of function. Loss of complex traits presumably relates to accumulated mutations and economic efficiency, but unfolds with no distinct pattern of distribution. [ABSTRACT FROM AUTHOR]

The largest animals are the rorquals, a group of whales which rapidly engulf large aggregations of small-bodied animals along with the water in which they are embedded, with the latter subsequently expulsed via filtration through baleen. Represented by species like the blue, fin, and humpback whales, rorquals can exist in a wide range of body lengths (8–30 m) and masses (4000–190,000 kg). When feeding on krill, kinematic data collected by whale-borne biologging sensors suggest that they first oscillate their flukes several times to accelerate towards their prey, followed by a coasting period with mouth agape as the prey-water mixture is engulfed in a process approximating a perfectly inelastic collision. These kinematic data, used along with momentum conservation and time-averages of a whale's equation of motion, show the largest rorquals as generating significant body forces (10–40 kN) in order to set into forward motion enough engulfed water to at least double overall mass. Interestingly, a scaling analysis of these equations suggests significant reductions in the amount of body force generated per kilogram of body mass at the larger sizes. In other words, and in concert with the allometric growth of the buccal cavity, gigantism would involve smaller fractions of muscle mass to engulf greater volumes of water and prey, thereby imparting a greater efficiency to this unique feeding strategy. [ABSTRACT FROM AUTHOR]

Despite its vital function in a highly dynamic environment, baleen is typically assumed to be a static material. Its biomechanical and material properties have not previously been explored. Thus I tested sections of baleen from bowhead whales, Balaena mysticetus, and humpback whales, Megaptera novaeangliae, alone or in groups representing miniature 'racks', in a flow tank through which water and buoyant particles circulated with variable flow velocity. Kinematic sequences were recorded through an endoscopic camera or viewing window. One set of experiments investigated particle capture; another series analyzed biomechanical behavior, including fringe spacing, movement and interaction. Baleen fringe porosity directly correlates, in a mostly linear fashion, with velocity of incident water flow. However, undulation and interaction of fringes (especially of bowheads) at higher flow velocities can decrease porosity. Fringe porosity depends on distance from the baleen plate. Porosity also varies, with fringe length, by position along the length of an individual plate. Plate orientation, which varied from 0 to 90 deg relative to water flow, is crucial in fringe spacing and particle capture. At all flow velocities, porosity is lowest with plates aligned parallel to water flow. Turbulence introduced when plates rotate perpendicular to flow (as in cross-flow filtration) increases fringe interaction, so that particles more easily strike fringes yet more readily dislodge. Baleen of bowhead whales, which feed by continuous ram filtration, differs biomechanically from that of humpbacks, which use intermittent lunge filtration. The longer, finer fringes of bowhead baleen readily form a mesh-like mat, especially at higher flow velocities, to trap tiny particles. [ABSTRACT FROM AUTHOR]

Comprehensive morphometric analysis of osteological and necropsy specimens indicates that blunt heads and wide jaws, both of which create a more circular mouth opening and thus improve water flow for suction feeding, are common in Odontoceti and found in all families except freshwater river dolphins (Platanistoidea), which are exclusively long-snouted. Mandibular bluntness, here termed amblygnathy, correlates with dental reduction in odontocetes; there is a further association of reduced dentition with increased body length. Examination of quantitative data reveals that many odontocetes, especially globicephaline delphinids, have a blunter cranial profile (partly from facial musculature and other soft tissues) and fewer exposed teeth for grasping prey than is generally supposed, especially when the researcher relies solely on examination of skeletal materials. Numerous teeth present in cleaned skulls and jaws remain unerupted even in adults, as verified by necropsy tooth counts, rendering tooth counts from museum specimens unreliable indicators of in vivo conditions. Amblygnathy and smaller, rounder mouth openings correlate with other anatomical, ecological, and behavioral traits associated with suction feeding. It is likely that odontocete suction ingestion evolved independently in multiple lineages from use of suction to transport grasped prey in long-jawed ancestors, with consequent loss of the grasp and transport step as prey are sucked directly into the oral cavity or oropharynx. [ABSTRACT FROM AUTHOR]