The findings are published in the Aug. 12 issue of the journal Nature.
The ear is the most important sense organ for modern toothed whales, say scientists, because these whales locate their prey using echolocation. Directional hearing is critical: A blind such whale could find food without much trouble; a deaf one would starve.
The study documents how hearing in these whales evolved. The research is based on cetacean fossils representing four groups of early whales. The earliest cetaceans, pakicetids (those that swam in ancient seas 50 million years ago), used the same sound transmission system as did land mammals, and so had poor underwater hearing. More recent cetaceans, remingtonocetids and protocetids (those that lived 43-46 million years ago), retained the land-mammal system, but also developed a new sound transmission system.
"The fossils document the ways in which cetacean hearing has changed, starting with ear fossils of whales' land ancestors and ending with the ear of near-modern looking whales," said Hans Thewissen, an anatomist at the Northeastern Ohio Universities College of Medicine (NEOUCOM). Thewissen and NEOUCOM researcher Sirpa Nummela led the study.
The newer system was similar to that of modern whales. The later whales could hear better in water than pakicetids could, and could also hear in air, but hearing in both media was compromised by the existence of two systems. With the advent of basilosauroids (approximately 40 million
Contact: Cheryl Dybas
National Science Foundation