BEIJING, Sept. 20 (Xinhuanet) -- When whales returned to the ocean from land 45 million years ago, they had nothing in common with bats. Seven million years later they did: echolocation, the ability to find and identify objects by emitting and bouncing sounds off them.

Fossils reveal toothed whales, such as the sperm whale, first developed this sonar-like ability.

Some marine biologists think that sonar in toothed whales came about as a better way to find food in the darkness of the deep ocean. But how did the whales know there were fish down there in the first place?

Researchers at the University of California, Berkeley, suggest close encounters with giant squid that migrated from the depths to the surface at night were the attraction.

"When whales developed sonar," explained researcher Nick Pyenson of the University of California, Berkeley, "it allowed them to dive deeper and follow the squids into the very dark ocean depths, where they discovered a rich food source that was accessible 24 hours day."

Cephalopods, such as squid, are the most abundant and high-energy resource in the ocean and are eaten by 90 percent of all toothed whales.

The researchers detailed their theory in the European journal Lethaia.

The development of echolocation in whales and bats are strong examples of how two very different species evolved similar adaptations to their environment and passed it down to succeeding generations, a process known as convergent evolution, Pyenson noted.

"With convergent evolution, we see the same solution for being able to chase after your prey in the dark," Pyenson said, "whether you're a bat or a whale."

(Agencies)