Meeting Abstract

89.3  Friday, Jan. 6  A putative sensory organ in the mandibular symphysis of rorqual whales (Balaenopteridae) PYENSON, N.D.*; GOLDBOGEN, J.A.; VOGL, A.W.; SZATHMARY, G.; DRAKE, R.; SHADWICK, R.E.; Smithsonian Institution; Cascadia Research Collective; University of British Columbia; FPinnovations; Cleveland Clinic; University of British Columbia pyensonn@si.edu

Marine vertebrates have evolved multiple solutions to the challenges of feeding in an aquatic medium. Large baleen whales belonging to the group Balaenopteridae, or rorquals, engulf and filter large volumes of prey-laden water at high speed by lunge-feeding. This feeding strategy is facilitated by several bony and soft tissue specializations, including unfused mandibles that loosely articulate with the skull and delimit the size of the oral cavity. Here we report the presence of an unusual organ located within the fibrous mandibular symphysis of rorqual whales. We investigated the properties and composition of this organ using gross macroscopic dissection, fine histological examinations, and digital imaging with x-ray CT and MRI techniques on several species of rorquals, including both fetal and adult specimens. These approaches revealed that the organ, located in the open mandibular symphysis, receives branches from neurovascular bundles that emerge from relictual alveolar foramina. Based on the preponderance of evidence, we argue that this structure is a sensory organ that responds to localized changes in jaw configuration during lunge-feeding. Furthermore, its anatomical location in the mandibular symphysis resolves a problematic linkage of specialized tissues (e.g., ventral groove blubber, Y-shaped cartilage) associated with the rapid and dramatic expansion of the oral cavity during a lunge. Beyond its biomechanical significance, this sensory organ also represents an evolutionary novelty, based on its absence in all other lineages of extant baleen whales, despite the antiquity of unfused mandibles in mysticetes since the Oligocene.