Hyperoodon echo-morphology: Biosonar anatomy in the northern bottlenose whale

Abstract

The northern bottlenose whale (Hyperoodon ampullatus) is one of the largest toothed whales, marked by an outsized bulbous forehead. Like other odontocetes, the head contains a sophisticated biosonar system. The in situ anatomic geometry of the biosonar components is normally inaccessible by the large size of these animals. We acquired a 400 kg head from a 6.18 m female Icelandic bottlenose whale. The head was encased in a special sarcophagus. An industrial CT scanner generated more than 700 scans at 2 mm thick, from which we reconstructed the detailed anatomy of the head. The acoustic fats are ensheathed in higher density (acoustically reflective) tissues that act to channel sounds into and out of the head. Lipid channels begin at both sets of phonic lips, coalesce into a single S-shaped channel that eventually passes between two large maxillary crests, and then forms a horn shaped melon that projects sound into the environment. Sounds are apparently received over the jaws and throat and travel back to the bony ear complexes through lipid pathways. These lipid channels bifurcate and insert onto the ear complex where the bone is thin. The finite element simulations for biosonar sound transmission and will be reported.