Michael G. Boudreaux

Jason Avery is a museum security guard. Ninjas break in to steal a glowing crystal dinosaur egg. The scientist/anthropologist/whatever behind the theft talks of it giving him the power to control harpies. Through a series of contrivances, the egg opens a portal that Jason promptly falls into, crash landing in the past in a land plagued by harpies. Conveniently, he gets roped into saving the villagers. A lot of hullabaloo involves a gold amulet and a villain seeking to gain control of the egg.