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Fossil of ancient whale sheds light on how cetacean sonar developed

Reuters

The deadly threat posed by German submarines during World War I helped spur scientists to develop sonar, using underwater sound signals to locate objects like subs.

It was an important breakthrough, but it was old technology as far as whales go. These marine mammals have been using echolocation — bouncing high-frequency sounds off underwater objects — to find prey for tens of millions of years.

U.S. scientists Wednesday announced the discovery of the most ancient whale known to have used echolocation — a creature called Cotylocara macei, which lived about 28 million years ago and was a bit larger than a bottlenose dolphin.

The discovery suggests that echolocation evolved in toothed whales — the group that includes modern varieties like sperm whales, killer whales, dolphins and porpoises — perhaps 32 million to 34 million years ago, the scientists said.

That was relatively soon after whales split into two major groups of cetaceans around 35 million years ago: toothed whales that were active hunters and toothless baleen whales that were filter feeders, straining food like krill from the ocean.

Jonathan Geisler, an anatomy professor at New York Institute of Technology who led the research, published in the journal Nature, called echolocation “an amazing trait.”

“It’s a sonarlike system which allows them basically to navigate and find food, particularly in waters where there’s little light, either at great depth or in very turbulent waters with a lot of mud, like estuaries or around marshes,” he added.

Cotylocara, whose fossilized remains include a 22-inch (56-cm) skull, neck vertebrae and ribs, was about 10 to 11 feet (3 to 3.4 meters) long and probably swam in a shallow ocean environment, feeding on fish and squid, Geisler said.

The fossils were unearthed near Summerville, South Carolina, outside Charleston, said College of Charleston geology professor James Carew, another of the researchers.

While Cotylocara looked superficially like some smaller modern toothed whales, it was not closely related to them.

“This is a member of an extinct family that split off very early from other echolocating whales, dolphins and porpoises. They went extinct 25 million or 26 million years ago, and they don’t have any living relatives,” Geisler said in an interview.

Whales that use echolocation produce very high-frequency vocalizations through a soft-tissue nasal passage located between the blowhole and skull. Other mammals, including people, produce sounds using the voice box, or larynx, inside the neck.

When air is pushed through the whale’s nasal passage, it produces extremely high-frequency clicks, squeaks and squeals that then echo off objects in the water, enabling the whale to get a high-resolution audio image of its surroundings.

“They can ‘see’ the fish, and then they know to swim in that direction to catch it,” Geisler said.

The sound-producing mechanism is complex, with big muscles, air pockets and bodies of fat — all in a small facial area.

The sound is too high for human ears to hear.

Modern whales that use echolocation possess a melon — a fat-filled organ in the head — that focuses the sound wave. Geisler suspects that Cotylocara already had this organ.

The whale’s genus name, Cotylocara, means “cavity head” in recognition of a very deep pocket atop its skull that is thought to be associated with an air sinus used in echolocation.

Whales are not the only animals that use echolocation. Bats, which first appeared more than 50 million years ago, use it while flying to pinpoint insects and other prey.

The first whales appeared more than 50 million years ago, arising from wolf-size land dwellers. Whales gradually became better suited to sea life and grew larger — one called Basilosaurus, which lived about 40 million years ago, was at least 56 feet (17 meters) long. Echolocation was a later adaptation.

  • Jamie Bakeridge

    Amazing animals. Which begs the question why the Japanese feel the need to keep killing them, and disingenuously claim it is done in the name of “research”.