CRANFORD, TW; MCKENNA, MF; San Diego State University: Acousticoadaptations in Deep Diving Toothed Whales

A recent spate of whale deaths has been associated with exposure to high intensity sound. These events have provided an impetus to study the anatomic geometry of the most effected, yet little-known group of cetaceans, the beaked whales (Family: Ziphiidae). Decades of research has provided significant understanding of the anatomy of acoustic transmission and reception in adult dolphins (Family: Delphinidae). Comparisons between the cephalic anatomy of an adult Cuvier�s beaked whale (Ziphius cavirostris) and an adult bottlenose dolphin (Tursiops truncatus), as shown by CT scans, yield numerous acoustically relevant similarities and differences. Chief among the anatomic differences is that Ziphius has a broad band of dense connective tissue that wraps around its melon in an arch that is anchored to the skull. The deep diving odontocetes, primarily sperm whales and beaked whales, have a pair of pterygoid sinuses with a surprisingly large capacity for air. All odontocetes possess pterygoid sinuses that narrow posteriorly before they ramify to form a series of pockets on the medial aspect of each bony hearing apparatus (tympanoperiotic). These diverticula are inflated through the Eustachian tube and are juxtaposed to an extensive fibrous venous plexus. The morphological relationships between the mandibular fat bodies and the bony hearing apparatus, the internal structure of the melon, and the bilateral structure of the phonic lips are largely similar across the entire suborder. These anatomic anomalies and commonalities may indicate different strategies for the deepest diving odontocetes. The tendency is for deep diving species to use dense connective tissue boundaries for acoustic beam formation. At the same time, they apparently reserve the air volume, which decreases with depth, to isolate the hearing complexes acoustically as a means to maintain directional hearing.