This came out over a week ago, and has been sitting around among my bookmarks – I couldn’t ignore it forever though. As reported on ScienceDaily, Migrating Squid Drove Evolution Of Sonar In Whales And Dolphins, Researchers Argue.
Lindberg, a specialist in the evolution of marine mollusks, noted that cephalopods have migrated up and down 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 number of squid hang out during the day at about 500 meters below the surface, though some go twice as deep. During the night, however, nearly half the squid are within 150 meters of the surface.
Over the millennia, cephalopod species in general – and especially shelled cephalopod species – fell as the number of whale species boomed, possibly because of predation by whales. Then, about 10 million years ago, the whales seem to have driven the nautiloids out of the open ocean into protected reefs. Lindberg said that the decline in nautiloid diversity would have forced whales to perfect their sonar to hunt soft-bodied, migrating squid, such as the Teuthida, which in the open ocean are typically two feet long or bigger and range up to the 40-foot-long giant squid.
So you see, migration was an effective strategy, until cetaceans joined in with their own sonar ‘arms race.’ Nifty.