ANIMALS - Frogs That Hear With Their Mouth: X-Rays Reveal a New Hearing Mechanism for Animals Without an Ear

Gardiner's frogs from the Seychelles islands, one of the smallest frogs in the world, do not possess a middle ear with an eardrum yet can croak themselves, and hear other frogs. An international team of scientists using X-rays has now solved this mystery and established that these frogs are using their mouth cavity and tissue to transmit sound to their inner ears.
http://www.sciencedaily.com/releases/2013/09/130902162712.ht