There are 30 Dinosaur Bones available to be found, but only 22 of them are accessible before the epilogue. You can find all 22 of the bones without having talked with Deborah MacGuiness, but you must talk with her before all 30 of the Dinosaur Bones can successfully be found. After finding and mailing all bone locations, Deborah MacGuiness will invite you to visit her at her workshop, along with sending you some rewards for your efforts along the way.