A study published in Diversity provides new insight into how toothed whales and dolphins came to navigate the underwater world using sound waves.

Whales and dolphins, which lack external ears, rely on a technique called echolocation to navigate and hunt in the dark. Much like shouting and listening for echoes, these animals emit high-pitched sounds that bounce off objects and reflect back at them, allowing them to map out their surroundings.

Their skulls and soft tissues near and within the blowhole are asymmetrical, meaning that a structure on one side is larger or differently shaped than its counterpart on the other side. This “lopsidedness” enables the production of sound. At the same time, a fat-filled lower jawbone conducts sound waves to the internal ear, allowing the animals to locate where sounds are coming from (directional hearing).

Yet, how whales and dolphins evolved this sophisticated “built-in sonar” is not fully understood.