A 27 million year old fossil from a species named Echovenator Sandersi, nicknamed Echo Hunter, had been found 15 years ago in South Carolina. Recently, it had been discovered that the features in its inner ear indicated that it could hear sounds too high pitched for the human ear. This species is a relative of the modern toothed whales like dolphins, porpoises, and sperm whales. Based on the Echo Hunter's skull and cranial features they were able to tell if this species could echo locate or not. By examining the inner ear, researchers found evidence of its ability to receive high frequencies. A soft tissue structure called the basilar membrane, not present on the fossil, but indicated by other parts of the ear to be of size and thickness consistent of high frequency hearing. A thick, bony part of the cochlea also provided further evidence of this ability. Toothed whales use echolocation to hunt for prey by emitting a series of high frequency chirps and navigating based on echoes. Dr Uhen believed that the development of high frequency hearing is a nice illustration of natural selection. Because of this newly discovered information, we now know that the use of navigational technique of echolocation goes back millions of years earlier in whales than previously known.
http://www.nytimes.com/2016/08/05/science/echo-hunter-whale.html?rref=collection%2Fcolumn%2Ftrilobites&action=click&contentCollection=science®ion=stream&module=stream_unit&version=latest&contentPlacement=2&pgtype=collection
http://www.eurekalert.org/pub_releases/2016-08/cp-wuh072816.php
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