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Fossilized Ear Shows Ancient Toothed Whales' Ultrasonic Hearing Emerged Much Earlier

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Modern toothed whales possess exquisite skills that help them survive underwater.

Indeed, these marine animals depend on a process called echolocation to hear the sound of their own calls, navigate underwater and hunt for food.

What's more, the animals' ability to hear high frequencies boosts their echolocation, scientists say.

The question is, how far back in evolution has high-frequency hearing been imprinted in toothed whales?

A new study conducted in South Carolina provides an explanation: toothed whales' ability to hear high frequencies may have emerged much earlier than anticipated.

Finding Fossils

Led by Morgan Churchill, a paleontologist from the New York Institute of Technology, researchers unearthed several fossils in a drainage ditch located in South Carolina.

One of those fossils is that of a newly discovered dolphin species known as Echovenator sandersi, which may have thrived in warm, shallow seas millions of years ago.

What's interesting about the find is the Echovenator's well-preserved ear — now considered as the best-preserved ear of any ancient cetacean, scientists say.

The finely preserved ears provide insight into the development of ultrasonic hearing in ancient whales. Churchill says high-frequency hearing may have preceded the appearance of echolocation.

Ultrasonic Hearing

The team of paleontologists used CT scan to investigate the remarkably complete fossilized ear of the Echovenator and compared it with that of two hippos, as well as that of living whales.

The analysis revealed many features also found in modern dolphins, researchers say.

In fact, the anatomy of the ancient toothed whale's ear indicates that high-frequency hearing evolved in whales about 27 million years ago.

The traits associated with ultrasonic hearing actually predate the emergence of toothed whales, the report explained.

Furthermore, the evolutionary ancestors of these modern marine animals may have had the ability to hear higher frequencies than their relatives on land.

Similarities To Modern Animals

Churchill says the Echovenator's inner ear is uncannily similar to the inner ear of modern whales.

Only one trait of the prehistoric animal's ear was more similar to primitive whales than to modern whales, indicating a very quick evolution of hearing abilities, Churchill says.

The Echovenator, which meant "echo hunter," was remarkably smaller than its ancestors at only about 6 feet (2 meters) long. The animal's front teeth, which is located on the end of a long, narrow snout, is well adapted for catching fish.

The process of echolocation is a crucial adaptation not only for whales, but for dolphins as well, because the skill could help them hunt down food successfully.

Meanwhile, the Echovenator is only one of many fossil whales that Churchill and the team are studying in South Carolina.

The remains, which represent the earliest known ancestors of toothed whales, mean that there must be more to come in the understanding of modern whale and dolphin evolution.

Details of the new study are published in the journal Current Biology.

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