Echolocation evolved in aquatic mammals about 30 million years ago during the Eocene period. Whales and other aquatic mammals like Dolphins, Seal, Porpoise etc use Ultra sound for navigation and predation. Whales live in an environment that has acoustic characters but with low visibility due to the turbidity of water. So they use the sonar mechanism for navigation. Whales, especially Toothed whale uses Bisonar system for echolocation. Bisonar in toothed whale uses two frequencies like FM and CF for locating the objects. Sonar is a system that detects objects through sound waves. The word SONAR is the acronym for SOund Navigation And Ranging.
Toothed Whales use the Bisonar system for navigation and predation. They emit ultrasound waves which pass through the water and hit back from the objects. They can sense these Echo back to determine the distance of the target.
Adaptations for Echolocation
Toothed whales possess a structure called Blow hole on the top of its head to produce ultra sound since Vocal cords are absent. The skull of Toothed Whale is asymmetric as an adaptation for echolocation. Brain is highly enlarged and there is poor connection between the hemispheres. A structure called Melon is present in the head to focus the ultrasound. The Melon is a fatty organ composed large quantity of lipids and act as an acoustic organ. Toothed Whale also lacks the sense of smell and they do not have salivary glands.
Communication through sound waves is well developed in Whales. They use two frequencies of ultrasounds for navigation. These frequencies include FM and CF frequencies. For communication and localization of targets, they use clicks of sounds .The click train has a repetition rate of 600 per second or more. These clicks are called Burst pulses and the auditory brain response resolves the individual clicks to produce the response. Whale emits a focused beam of high frequency clicks which passes from the nostrils through the Phonic lips. The sound waves are reflected by the concave bone of the cranium and an Air Sac present below it. The Melon modulates the sound frequency. Echo is received by the fatty structures present around the lower jaw. From there, the sound travels to the middle ear. Lateral sound is received through the fatty lobes present around the ear. The highly enlarged brain can interprets the echo and determines the distance, direction etc of the target.