So with all the controversy of Navy sonar, I thought I'd share an article I found about whales' hearing ...

Evolution of Whale Hearing Unfolds in Fossil Record

An international team of scientists has traced the evolution of hearing in modern cetaceans (whales, dolphins and porpoises). "This study of the early evolution of whales demonstrates the changes that took place in whales' outer and middle ears, required for the transition from a land-based to a marine-based existence," said Rich Lane, director of the National Science Foundation (NSF)'s geology and paleontology program, which funded the research. 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.

Reconstruction of the remingtonocetid Kutchicetus. It was a small animal, no bigger than a river otter. Illustration by Carl Buell and taken from http://www.neoucom.edu/Depts/Anat/Remi.html.

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,.

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 years ago), the old land-mammal ear disappeared, and the modern cetacean sound transmission system began its development. Although basilosaurids were not echolocators (they lacked the sound-emission equipment of later echolocators), they had taken a major step forward in refining underwater sound reception.