Fossilised whale skull reveals that the creature's incredible ultrasonic hearing evolved 27 million years ago
- Experts studied one of the best preserved ears of any ancient whale
- Found Echovenator sandersi would have heard ultrasonic frequencies
- Suggests toothed whales' ability to hear evolved 27 million years ago
From playful dolphins to huge sperm whales, all modern toothed whales rely on echoes of their own calls to navigate the ocean and hunt underwater.
Now researchers have discovered the whales’ ability to hear high frequencies inaudible to humans evolved earlier than previously thought.
They studied one of the best preserved ears of any ancient whale ever discovered to find high-frequency hearing evolved 27 million years ago.
Echovenator sandersi (illustrated) had the ability to echolocate. In this illustration, sound is produced by an ancient Echovenator, which bounces off prey to create echoes. They are detected via conduction of vibrations though the mandible and received by the inner ear
‘Our study suggests that high-frequency hearing may have preceded the emergence of echolocation,’ said Morgan Churchill of New York Institute of Technology in Old Westbury, New York.
Dr Churchill made the discovery when studying a new fossil whale species (Echovenator sandersi) found in a drainage ditch in South Carolina.
His team put the whale’s remarkably complete fossilised ear a in a CT scanner and compared its structure to those of two hippos and 23 species of living and extinct whales.
The analyses uncovered many features found today in dolphins, which can hear at ultrasonic frequencies and use them to find and catch prey.
Porpoises have the highest known upper hearing limited of all modern toothed whales, at around 160kH. For comparison, our own upper limit is around 20kHz, due to limitations in the middle ear.
The experts studied one of the best preserved ears of any ancient whale ever discovered to find high-frequency hearing evolved 27 million years ago. Its skull is pictured
The anatomy of Echovenator's ear suggests that high-frequency hearing evolved early in whale evolution, about 27 million years ago and that traits associated with this ability predate the emergence of toothed whales.
It also suggests the ancestors of toothed whales could hear at higher frequencies than their relatives on land, according to the study, published in the journal Current Biology.
Dr Churchill says that the inner ear of Echovenator is surprisingly similar to that of modern whales.
Dr Churchill says that the inner ear of Echovenator (ear bone pictured above from different angles) is surprisingly similar to that of modern whales
In fact, only one trait of the ancient whale's ear was more similar to primitive whales than to modern whales, suggesting a very rapid evolution of hearing abilities in early whales.
He told MailOnline: 'Echovenator would have looked pretty similar to many dolphins of today.
'It was small, only around 2 metres long, and probably similar in size to a modern harbour porpoise.
'The most obvious difference would be in its teeth and the position of its blowhole.
'Today modern porpoises and dolphins have very simple conical teeth - in contrast echovenator had more complex triangular teeth with multiple cusps. These teeth would have been placed along a set of long, thin, bony jaws.
'Modern dolphins have a single blowhole which is placed on the top of the head.
This diagram shows the evolution of hearing shapes, focusing on differences in the ear structure between species or whale with high frequency hearing - either infrasonic or ultrasonic, including E. sandersi (second from right)
'Echovenator would in contrast have had a much more forward facing blowhole. It is also possible that Echovenator would have had paired openings for this feature, rather than a single opening.'
He also said the ancient whale was remarkably small compared to its ancestors, suggesting a drastic change in body size early in toothed whale evolution that most likely influenced a range of variables, from brain size to ecology.
Echovenator is just one of many fossil whales from South Carolina that Dr Churchill and colleagues are in the process of studying.
The fossils represent some of the earliest known ancestors of toothed whales and experts hope they will shed light on the evolution of cetaceans’ intelligence, body size, foraging ecology, and diversity in modern whales.
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