From last August, here's Jeanette Strole Parks on Dollar Store Crafts outlining a method for turning a paper plate into a set of shark jaws:
1. Fold your paper plate in half "backwards" (with the bottom of the plate facing you, and the folded edges coming toward you).
2. Using small scissors trim away the outer edges of the plate in a sweeping arched "M" design on the top half and bottom half, which should leave it looking like the hinges on the jaw, and the "m" shaped bottom & top of the mouth. Look at pictures on Google of real shark jaws to get inspiration, if the craft-samples in the photos don't help you visualize the outline.
3. Cut out a large oval from the middle, and then work from that center to cut out free-form teeth that follow the inside arc of the paper plate on the top and bottom. I just snipped away happily. Shark teeth are often quite irregular and jagged and not always parallel.