Animal Crossing: Wild World/Fossils

Fossils are buried in the ground. If you see a brown star-looking thing, get your shovel and stand right in front of it. Press, and you'll either get a gyroid or a fossil. If you get a fossil, take it to the museum and have Blathers identify it. If Blathers asks for the fossil, it is a good idea to give it to him. If you give it to him, he'll put it on display. If you don't want to give it to him, you can sell it to Tom Nook for at least 1,000 bells! There are 52 kinds of fossils in the game. After filling up the Museum, you can just sell the fossils to make money.

If you dig up a gyroid, you can put it in your house or sell it to Tom Nook for several hundred bells or more. They come in different sizes- most sizes have a mega, mini, tall, normal, wee, and slim variety. You can dig up 127 gyroids. After selling them, you can't buy them back from the catalog, so be sure you want to sell before you get rid of them.