 The adaptation of echolocation occurred when toothed whales ( Odontoceti ) split apart from baleen whales , and distinguishes modern toothed whales from fully aquatic archaeocetes . This happened around 34 million years ago in a second cetacean radiation . Modern toothed whales do not rely on their sense of sight , but rather on their sonar to hunt prey . Echolocation also allowed toothed whales to dive deeper in search of food , with light no longer necessary for navigation , which opened up new food sources . Toothed whales echolocate by creating a series of clicks emitted at various frequencies . Sound pulses are emitted , reflected off objects , and retrieved through the lower jaw . Skulls of Squalodon show evidence for the first hypothesized appearance of echolocation . Squalodon lived from the early to middle Oligocene to the middle Miocene , around 33 – 14 million years ago . Squalodon featured several commonalities with modern toothed whales : the cranium was well compressed ( to make room for the melon , a part of the nose ) , the rostrum telescoped outward into a beak , a characteristic of the modern toothed whales that gave Squalodon an appearance similar to them . However , it is thought unlikely that squalodontids are direct ancestors of modern toothed whales . 
