Mandible allometry in extant and fossil Balaenopteridae (Cetacea: Mammalia): the largest vertebrate skeletal element and its role in rorqual lunge-feeding

Rorqual whales (crown Balaenopteridae) are unique among aquatic vertebrates in their ability to lunge-feed. During a single lunge, rorquals rapidly engulf a large volume of prey-laden water at high speed, which they then filter to capture suspended prey. Engulfment biomechanics are mostly governed by the coordinated opening and closing of the mandibles at large gape angles, which differentially exposes the floor of the oral cavity to oncoming flow. Mouth area in rorquals is delimited by unfused bony mandibles that form kinetic linkages to each other and with the skull. The relative scale and morphology of these skeletal elements have profound consequences for the energetic efficiency of foraging in these gigantic predators. Here we performed a morphometric study of rorqual mandibles using a dataset derived from a survey of museum specimens. Across adult specimens of extant balaenopterids, mandibles range in size from ~1-6 m in length, and at their upper limit they represent the single l...