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So, I have an aquatic humanoid species that I want to be able to use echolocation. They are extremely similar to humans,with some minor differences, like gills. (The reason I include this tidbit is because I understand that dolphins use their jaw to channel sounds to their ears.)

A problem I've run into is that I don't really know what makes whales and dolphins good at using sonar. I know humans can develop a kind of echolocation, especially if blind, but as I understand it sounds above water are very different from sounds in it.

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    $\begingroup$ Have you tried googling "How does a dolphin echolocate" $\endgroup$ – Aify May 9 '16 at 2:16
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    $\begingroup$ @Aify Yes, and while that certainly helps in regard to porpoises, what about a humanoid creature that doesn't look like a dolphin or have the jaw of one? $\endgroup$ – Xandar The Zenon May 9 '16 at 2:26
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    $\begingroup$ It seems you can'y get out of drastically changing the aquatic humans' head structure. The sound emitted could simply be an adapted voice box, but it seems the melon and some kind of sound receiving surface like the jaw of a dolphin (as well as internal structures to prevent confusion between sounds) are necessary. $\endgroup$ – XenoDwarf May 9 '16 at 3:15
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    $\begingroup$ Gills are by no means a minor difference. The branchial clefts of fish are what gave rise eventually to our ears. And if you have gills, you don't have lungs. If you don't have lungs, you don't need separate thoracic and abdominal cavities. These design changes are so daunting that adding echolocation would be a walk in the park in comparison. $\endgroup$ – frank May 9 '16 at 6:25
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Two places that would have changes from the usual human structure are the ear and brain. With just a few alterations to these organs and you could have a humanoid creature that could use echolocation effectively enough to "see" under water

Dolphins can produce clicks with their vocal cords; your humanoid should be able produce a similar sound. If not, some slight change of their vocal cords should make it possible.

It is possible for the human brain to learn to interpret sound as sight. However, the human brain is not set up to be used this way and can't do as effectively as a dolphin. Dolphin brain is optimized for interpreting sound into sight. Your humanoids would probably have a brain that was a hybrid between a human brain and dolphins.

Other changes would be in the ear. The Bottle-nose Dolphin hears tones with a frequency up to 160 kHz with the greatest sensitivity ranging from 40 to 100 kHz. The average hearing range for humans is about 0.02 to 20 kHz. So your humanoids' echolocation would much more efficient if their ear structure was more like a dolphin then a human. specifically changes you should make would be to the mechanical stiffness of the middle ear and the cochlear input impedance. These changes would alter the middle-ear transfer function. The dolphin ear also has some-filled sinus pockets that allow for greater directional hearing underwater.

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  • $\begingroup$ So, how would I go about changing it to be more like a dolphin's? How would the ear shape be different? What about the jawbone shave? It's pretty much a given that these creatures have to be similar to a dolphin, but what exactly does that entail? $\endgroup$ – Xandar The Zenon May 9 '16 at 3:42
  • $\begingroup$ @XandarTheZenon I don't think a Jabone shave will be necessary, make no mistake it would certainly make the echolocation better, but I don't think not have it would be too much of a handicap. You appear to be asking for more details, I going to bed know but hopefully some time tomorrow morning I can add more details. $\endgroup$ – Bryan McClure May 9 '16 at 4:30

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