[brudgers]

I looked at the picture of the elephant and thought infrasound makes sense.

The size of elephant ears would probably work better with longer wavelengths.

[gus_massa]

My guess is that the deciding factor is the throat.

Yuo can have tiny ears if it would be better, but you need a throat of the corrrect size for breathing and eating.

[Terr_]

If the longer wavelengths are useful because they aren't impeded by obstacles like masses of forest leaves, then the same properties probably mean ear-flaps aren't really effective to shape/concentrate them either. (Although they could be used as a filter to block out higher frequencies.)

[joshuaheard]

I think the large ears are for cooling the big bodies.

[neonnoodle]

Yeah. Think about wooly mammoths - tiny/no external ears.