The purpose of this legislation is to officially designate the American mastodon as the national fossil mammal and the Tyrannosaurus rex as the national fossil dinosaur of the United States. This act aims to recognize and celebrate these significant prehistoric creatures, highlighting their importance in American natural history. Key provisions of the legislation include the formal designation of the American mastodon, scientifically known as Mammut americanum, and the Tyrannosaurus rex as the national fossil mammal and dinosaur, respectively.