The authors of the research paper looked at the evolution of whales and cephalopods to try and come up with a theory about the evolution of toothed whale echolocation. This is what they came up with (according to Science Daily):
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.
Bats also make an appearance (also from Science Daily):
“Whales, like bats, developed a sensory system for seeing with sound, and every single toothed whale echolocates in a different way, just like how different bat species echolocate in different ways,” Pyenson said. Whales also partition the water column, specializing in harvesting squid at specific depths, just as bats partition the tree canopy and preferentially hunt insects at specific heights.
Lindberg noted that whales and bats are strong examples of convergent evolution to take advantage of unexploited food resources: nocturnal insects, in the case of non-migrating insectivorous bats, and nocturnal cephalopods, in the case of whales. And just as predominately migrating fruit bats do not echolocate, so filter-feeding baleen whales that depend on dense seasonal resources lack biosonar.
I haven’t managed to come up with the Lethaia paper yet, so I can’t really go into more detail, but this sounds like a fascinating piece of research. It combines paleontology with studies of modern whale/squid behaviors, ecology and a whole host of other disciplines to try and understand the evolution of echolocation in whales. Fascinating stuff…