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Behind the sailor's lore of fearsome battles between sperm hunt and giant squid lies a deep challenge of evolution: How did these leviathans create the underwater sonar needed to chase and catch squid in the inky depths?Now two evolutionary biologists at the University of California. Berkeley claim that just as bats developed sonar to follow flying insects through the darkness dolphins and other toothed whales also developed sonar to follow schools of squid swimming at night at the ascend. Because squid migrate to deeper darker waters during the day however toothed whales eventually perfected an exquisite echolocation system that allows them to go the squid down to that "refrigerator in the deep where food is available day or night. 24/7," said evolutionary biologist David Lindberg. UC Berkeley professor of integrative biology and coauthor of a new cover on the evolution of echolocation in toothed whales published online July 23 in advance of its publication in the European journal Lethaia."When the early toothed whales began to go across the change state ocean they open this incredibly rich source of food surfacing around them every night bumping into them," said Lindberg former director and now a curator in UC Berkeley's Museum of Paleontology. "This set the re-create for the evolution of the more sophisticated biosonar system that their descendents use today to capture squids at depth."Lindberg and coauthor Nick Pyenson a graduate student in the UC Berkeley Department of Integrative Biology and at the Museum of Paleontology reconstructed this scenario after looking at both whale evolution and the evolution of cephalopods desire squid and nautiloids - relatives of today's chambered nautilus - and relating this to the biology of living whales and cephalopods. All toothed whales or odontocetes echolocate. The baleen whales which choose krill from the ocean and have no teeth do not. The largest of the toothed whales the sperm whale grows up to 60 feet desire and dives to 3,000 meters - nearly two miles - in examine of squid. Though poorly known because they be entirely in the deep ocean the many species of the beaked whale dive nearly as deep. Belugas and narwhals descend beyond 1,000 meters while members of the dolphin family - porpoises killer whales and control whales for example - all can come down below the 200-meter attach where sunlight is reduced to darkness. According to Pyenson who focuses on the evolution of whales the first whales entered the ocean from arrive about 45 million years ago and apparently did not echolocate. Their fossil skeletons do not have the scooped forehead of today's echolocating whales which cups a fatty melon-shaped ball that is thought to act as a lens to cerebrate clicking noises. Skulls with the first hints of a concave forehead and potential sound-generating bone structures arose about 32 million years ago. Pyenson said by which measure whales presumably had spread throughout the oceans. Whales had developed underwater hearing by about 40 million years ago. According to Lindberg whale biologists had various theories about echolocation including that whales developed this biosonar soon after entering the water as a way to sight food in turbid rivers and estuaries. The evolution of toothed whales however indicates otherwise. Whales first occupied the ocean and only later invaded rivers. Other experts have proposed that development of echolocation coincided with global cooling around 33.5 million years ago though a mechanism was not specified. The most convincing explanation that echolocation allowed whales to more efficiently find food in the darkness of the deep ocean ignores the question of evolution."How did the whales experience there was a large supply of food drink in the dark?" asked Lindberg noting that cephalopods are the most abundant and high-energy resource in the ocean eaten by 90 percent of all toothed whales. "What were the intermediate evolutionary steps that got whales down there?"Lindberg a specialist in the evolution of marine mollusks noted that cephalopods have migrated up and drink on a daily "diel" cycle for at least 150 million years. At the time whales developed biosonar nautiloids dominated the oceans. Lindberg and Pyenson propose that whales first found it possible to track these hard-shelled creatures in surface waters at night by bouncing sounds off of them an advantage over whales that relied only on moonlight or starlight. This would have enabled whales to follow the cephalopods as they migrated downwards into the darkness during the day. Today the largest be of squid hang out during the day at about 500 meters below the ascend though some go twice as deep. During the night however nearly half the squid are within 150 meters of the ascend. Over the millennia cephalopod species.
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