Modern dolphins fine-tuned their ability to echolocate –- using high-frequency sounds and their echoes to communicate, navigate and hunt –- at least 26 million years ago, according to a new fossil analysis.
In a study out of Monash University and Australia's Museum Victoria, researchers examined the 26-million-year-old ear bone of a xenorophid whale, one of the earliest ancestors of modern toothed whales - a group that includes dolphins as well as sperm whales, beaked whales and porpoises.
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Using CT scanning, the scientists were able to view the ear bone's structures in sharp detail.
The cochlea of the ancient animal, the team found, was specialized for the ability to sense high-frequency sound. And that looked familiar.
"When I first looked at the inner ear of the xenorophid, I was blown away by just how similar this incredibly old toothed whale was to a modern echolocating dolphin," said study lead Travis Park, of Monash University and Museum Victoria, in a statement.
Echolocation allows some animals, such as bats and dolphins, to emit sounds and use their return echoes to map things in their world - from prey to predator to inanimate object. It's a kind of "sight" that's considered an evolutionary advantage that helped animals in the toothed whale category spread and diversify across the Earth.
The similarity between the ancient toothed whale's inner ear and that of today's dolphin, the researchers say, solves a long-running mystery of just when dolphins first evolved their ability to echolocate.
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The finding also confirmed that ancient toothed whales could echolocate at all.
Researchers had previously thought the creatures could make high-frequency sounds. "But no one had actually ever looked to see whether they could actually hear these high frequency sounds as well," as Park told ABC Online's Rachel Brown.
Still unanswered, say the scientists, is what came before these super-sonic marine mammals.
"Our paper shows even the earliest known fossil odontocetes [toothed whales] have all the tools for echolocation seen in living dolphins," said study co-author Erich Fitzgerald, of Museum Victoria. "But they must have evolved from something that didn't quite have all the tricks of the odontocete trade."
Just how those earlier creatures evolved their way toward their future sonic prowess, then, remains an open question.
Park, Fitzgerald, and co-author Alistair Evans have published their findings in the journal Biology Letters.