Shark-tooth pattern

The shark-tooth pattern (known as the shark tooth prior to ) is a standalone fossil introduced in that appears in all subsequent games.

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
Helicoprion was a shark-like fish that lived off the southwestern coast of Gondwana in the Early to Middle Permian. While it is more closely related to sharks and other cartilaginous fishes than the bony fishes, its closest living relatives are actually the chimaeras, or rat fish. Like most cartilaginous fish, Helicoprion's body would have decayed quickly. As such, the only fossils found so far have been those of its tooth whorl. First described in 1899, the tooth whorl had baffled paleontologists for over a century, with ideas for what part of the body it was on ranging from the snout to the dorsal fin, to (possibly the most famous early idea) the outside of the lower jaw. Finally, in 2013, researchers working with related species discovered that the tooth whorl in fact sits inside the lower jaw. The whorl grows as Helicoprion ages, with newer teeth growing on the outside while the older teeth get pushed towards the middle of the spiral.