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Ancient Whale Skull Reveals Evolutionary Origins of Echolocation in Marine Mammals

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Mar 13, 2014 01:18 PM EDT
skull of the 28-million-year-old Cotylocara macei.
Evidence of the most ancient whale known to have used echolocation was announced Wednesday in the journal Nature. Pictured is the skull of the 28-million-year-old Cotylocara macei. Its anatomy and density variation indicate that this early toothed whale used echolocation to find its prey.
(Photo : James Carew and Mitchell Colgan )

Evidence of the most ancient whale known to have used echolocation was announced Wednesday in the journal Nature.

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Humans have been using echolocation in the form of sonar since the early part of the 20th century, but whales have made use of the ability to use sound to pinpoint locations for tens of millions of years. As evidenced in the fossils - which belong to a new species of ancient whale named Cotylocara macei - cetaceans have been using echolocation for at least 30 million years.

"The most important conclusion of our study involves the evolution of echolocation and the complex anatomy that underlies this behavior," said lead study author Jonathan Geisler, a professor of anatomy at the New York Institute of Technology College of Osteopathic Medicine. "This was occurring at the same time that whales were diversifying in terms of feeding behavior, body size, and relative brain size."

Cotylocara macei was a relative of modern-day toothed whales, dolphins, and porpoises and was a bit larger than a bottlenose dolphin. Cetaceans like these use a nasal passage beneath their blowholes to produce the high-frequency vocalizations used in echolocation. The mechanisms underlying the cetacean's ability to produce sound is complex, relying upon large muscles, air pockets and bodies of fat crammed into a small area.

The Cotylocara macei fossils give scientists a clearer picture of the evolutionary history of echolocation, while also providing evidence that the whale itself was capable of echolocation.

"Its dense bones and air sinuses would have helped this whale focus its vocalizations into a probing beam of sound, which likely helped it find food at night or in muddy water ocean waters," Geisler said.

The Cotylocara macei fossils, which were discovered near Summerville, South Carolina, consist of a 22-inch skull, neck vertebrae and ribs. The creature was about 11 feet long and possibly swam in shallow waters, Geisler told Reuters.

The marine mammal had an unusual, deep cavity atop its head, and a radar-dish like shelf of bone around its nasal openings which may have been used in echolocation.

"The anatomy of the skull is really unusual. I've not seen anything like this in any other whale, living or extinct" Geisler said.

The discovery suggests that echolocation evolved in toothed whales between 32 million and 34 millions years ago, after cetaceans underwent an evolutionary split between toothed whales and toothless, filter-feeding whales. The scientists reached this conclusion through analyzing the evolution of the entire toothed whale family tree.

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