You don't actually "dig" for fossils in Animal Crossing. You discover them already partially unearthed, sticking out of the ground!

Here's how it works:

1. Look for cracks in the ground: Fossils appear as small, brown cracks in the ground.

2. Use your shovel: Dig up the cracks with your shovel.

3. Unearth the fossils: Once you've dug a bit, you'll find the fossil partially sticking out.

4. Collect the fossil: Press "A" to collect the fossil and add it to your inventory.

You can then donate fossils to the museum to help complete the exhibit!