The veteran Aerosmith singer drew some howls from the judges, who recognized the 64-year-old rocker when he was introduced as a typical "Idol" hopeful named Pepper LaBieja.
"Steven Tyler is in the house," cheered Randy Jackson.
Mariah Cary quipped, "Dude looks like a lady," a reference to the Aerosmith hit by the same name.
CNN said Randy Travis recognized the prank immediately while Jackson, Cary and Niki Minaj seemed to need a few moments to catch on.
The Oklahoma auditions were the final round of tryouts before the selection process moves to Hollywood, the New York Daily News said.
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