DAVID GREENE, HOST:
Good morning. I'm David Greene. An Oklahoma teacher asked her fifth graders to each bring in a rock. She said any old rock would do. One student brought in a stone he tripped on in his backyard. It was about four inches wide and shaped like a tooth. Teacher Amy Duvall suspected the rock was a fossil, so she took it to a local museum. Turns out it was a tooth. According to the Muskogee Daily Phoenix, it belonged to a mastodon. The tooth may be up to 40 million years old. You're listening to MORNING EDITION. Transcript provided by NPR, Copyright NPR.