This newly identified fossil whale species could hear frequencies far above the range of human hearing, new research published in the August 4 edition of the peer-reviewed journal Current Biology has revealed.
The new species, which was identified by a team of researchers from the New York Institute of Technology and the National Museum of Natural History in France, was an ancestor of modern dolphins and has been named Echovenator sandersi (“Echo Hunter”) due to its auditory abilities.
The discovery suggests that whales first developed high-frequency hearing some 10 million years earlier than previous research had indicated, according to lead author Morgan Churchill, who is a postdoctoral fellow at the NYIT College of Osteopathic Medicine and his colleagues.
“Previous studies have looked at hearing in whales but our study incorporates data from an animal with a very complete skull,” Churchill said in a statement. “The data we gathered enabled us to conclude that it could hear at very high frequencies, and we can also say with a great degree of certainty where it fits in the tree of life for whales.”
“This was a small, toothed whale that probably used its remarkable sense of hearing to find and pursue fish with echoes only,” added co-author and associate professor Jonathan Geisler. “This would allow it to hunt at night, but more importantly, it could hunt at great depths in darkness, or in very sediment-choked environments.”
The fossil of Echovenator sandersi. (Credit: Jonathan Geisler)
Findings could help determine what ear features hear different noises
High-frequency hearing, Geisler explained, is one of two primary traits required for echolocation, or the use of sound waves and their echoes to establish the location of objects. Like bats, some whales use echolocation to hunt, but doing so requires them to have the ability to produce a high-frequency call, as well as the ability to hear and interpret those noises.
The study, which was part of a series of research projects funded through a $220,000 grant to the associate professor’s team from the National Science Foundation (NSF), verified that most of the characteristics associated with high-frequency hearing in whales emerged about 27 million years ago, around the same time as echolocation. Some features, however, evolved even earlier.
Churchill, Geisler and their fellow researchers analyzed the skull of a 27-million-year-old whale specimen discovered 15 years ago in South Carolina. They focused on the bony support structure of the inner ear membranes, as well as its surroundings, and found that the species now known as Echovenator possessed ultrasonic hearing abilities, meaning that it could detect frequencies well beyond the range of human hearing.
While scientists know that the semi-aquatic predecessors of modern whales that lived about 60 million years ago had limited high-frequency hearing abilities, statistical analyses performed by the authors of the new study enabled them to determine that at least some characteristics linked to this ability evolved in whales before echolocation, eventually becoming more refined.
“Knowing when and how echolocation evolved is a critical step in our project,” Geisler noted, “and we are studying how the evolution of echolocation influenced the evolution of skull shapes in cetaceans.” He added that as biological studies turn ever more to computer models, his team’s study could help determine what inner ear features are necessary for hearing sounds at different frequencies.
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Image credit: A Gennari 2016
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