Evolution of Echolocation

Over in the thread "A Most Promising Anti-Evolutionist" over at the Evolution/Creation section of Internet Infidels Discussion Board there was a creationist who called himself "Charles Darwin" who responded only to that thread.He had maintained that echolocation is unevolvable, and he maintained that creationism could be considered refuted only by presentation of a "compelling" naturalistic alternative. And about echolocation, he demanded the presentation of all the details of how it had evolved before he could accept that it had evolved.He'd present details like how echolocating bats have middle-ear muscles that muffle their ears as they chirp (it's rather difficult for a bat to cover its ears with its wings, let alone stick its fingers in its ears, as it flies).However, such muscles are a common feature of mammalian middle ears, and many species of bats simply make more use of them. All that is necessary is for a "make a chirp" brain command to also command temporarily muffling the ears.