A. Wayne Vogl, Margo A. Lillie, Marina A. Piscitelli, Jeremy A. Goldbogen, Nicholas D. Pyenson, Robert E. Shadwick

Rorqual whales (Balaenopteridae) are among the largest vertebrates that have ever lived and include blue (Balaenoptera musculus) and fin (Balaenoptera physalus) whales. Rorquals differ from other baleen whales (Mysticeti) in possessing longitudinal furrows or grooves in the ventral skin that extend from the mouth to the umbilicus. This ventral grooved blubber directly relates to their intermittent lunge feeding strategy, which is unique among vertebrates and was potentially an evolutionary innovation that led to gigantism in this lineage [1]. This strategy involves the rorqual whale rapidly engulfing a huge volume of prey-laden water and then concentrating the prey by more slowly expelling the water through baleen plates (Figure 1A). The volume of water engulfed during a lunge can exceed the volume of the whale itself [2]. During engulfment, the whale accelerates, opens its jaw until it is almost perpendicular to the rostrum, and then the highly compliant floor of the oral cavity is inflated by the incoming water [3]. The floor of the oral cavity expands by inversion of the tongue and ballooning of the adjacent floor of the mouth into the cavum ventrale, an immense fascial pocket between the body wall and overlying blubber layer that reaches as far back as the umbilicus. The ventral grooved blubber in fin whales expands by an estimated 162% in the circumferential direction and 38% longitudinally [4]. In fin whales, multiple lunges can occur during a single dive, and the average time between lunges is just over forty seconds [3]. Here, we show that nerves in the floor of the oral cavity of fin whales are highly extensible.