Shark Tooth

The Shark Tooth is a standalone fossil introduced in that appears in all subsequent games except.

In
After donating the fossil in, its plaque in the museum will read:

"The fossilized shark tooth has a distinctive serrated edge, like a steak knife. Sharks have existed since before the dinosaurs, but their appearance seems to have hardly changed at all. Their age actually puts them at a time even before plants had fully propagated over every continent."

Real-world information
Sharks can have up to 50,000 teeth in their lifetime. The tooth itself can be used to identify the kind of shark it came from.