Sling, Scoop, and Squirter: Anatomical Features Facilitating Prey Transport, Processing, and Swallowing in Rorqual Whales (Mammalia: Balaenopteridae)

Abstract

Much is known about lunge feeding in balaenopterid whales, but many key aspects of structure, function, and behavior have not yet been explained in detail, especially with regard to concentrating, positioning, and swallowing large aggregations of prey. We describe a novel system of three integrated structural components, all of which are involved in sequential feeding activities (intraoral transport, filtration, and swallowing of prey) that follow lunge-feeding engulfment of prey-laden water in rorquals: (1) a hammocklike muscular sling comprising extrinsic lingual musculature along the midline of the ventral pouch; (2) the flattened scoop-like arrangement of caudalmost baleen plates converging in the oropharynx adjacent to the esophageal opening; and (3) a flow-diverting flange at the posterior dorsum of the lip, by a flow channel at the angle of the mouth. Subsequent to contraction of the ventral pouch and concomitant expulsion of the mouthful of ingested water, these three structures together, we contend, aid in (1) channeling prey posteriorly toward the esophageal opening; (2) concentrating prey as excess water is squeezed from (what is presumed to be) the slurry-like mixture of nektonic and/or planktonic prey and water; and (3) guiding prey into the isthmus of the fauces while simultaneously (4) facilitating expulsion of water. These related functions occur along with, and are in part achieved by, elevation and retraction of the tongue and oral floor. Given their presumed functional role, these systems are best described as a suite of integrated structural adaptations.

Multiaxial movements at the minke whale temporomandibular joint

“…These video sequences and publications, although sparse, nonetheless confirm the types and degrees of mandibular movements obtained in our study. For example, the maximal rorqual gape described in the literature is approximately 90° (Arnold et al, ; Werth & Ito, ), which accords with the maximal gape angle (96°) obtained from our manipulation of minke whale specimens.…”

“…For example, the maximal rorqual gape described in the literature is approximately 90 (Arnold et al, 2005;Werth & Ito, 2017), which accords with the maximal gape angle (96 ) obtained from our manipulation of minke whale specimens.…”

“…Nonetheless, we did include, as part of our analysis, review of videorecorded feeding sequences as well as publications that describe mandibular and oral movements based on tag data from live animals (Goldbogen, Pyenson, & Shadwick, ; Potvin et al, ) or that relate rorqual feeding morphology to kinematic analysis of video sequences (Arnold et al, ; Werth & Ito, ). These video sequences and publications, although sparse, nonetheless confirm the types and degrees of mandibular movements obtained in our study.…”

“…Rorquals include humpback ( Megaptera novaeangliae ), fin ( Balaenoptera physalus ), and blue whales ( Balaenoptera musculus ), the largest animals that have ever lived. During ram‐propelled lunge feeding on schooling zooplankton and fish (Figure ), the mouth opens wide to engulf enormous volumes (5–80+ m 3 ) of prey‐laden water (Goldbogen, ; Goldbogen et al, ; Lambertsen, ; Pivorunas, ; Potvin, Goldbogen, & Shadwick, ; Werth et al, ; Werth & Ito, ).…”

Prenatal Development of the Humpback Whale: Growth Rate, Tooth Loss and Skull Shape Changes in an Evolutionary Framework

“…Cetaceans (baleen whales or Mysticeti and toothed whales or Odontoceti) evolved from terrestrial ancestors related to modern artiodactyl taxa such as hippos and cows (Gatesy et al, ) during the Eocene, between 55 and 37 million years ago (Thewissen et al, ; Uhen, ). Through extreme modifications of their skull anatomy, in concert with behavioral and physiological adaptations, cetaceans acquired new feeding strategies enabling them to live exclusively in the marine environment (Werth, ; Goldbogen et al, ; Werth and Ito, ). One of the most striking morphological changes in the cetacean skull is telescoping, defined as the overlapping of the bones posterior to the rostrum to accommodate migration of the external nares to the top of the skull.…”