Dunkleosteus

Dunkleosteus is a standalone fossil: one piece completes it. Dig up fossils at the cracks on the ground, have Blathers assess them, then donate it to the museum or sell spares for 3,500 Bells.

Dunkleosteus was an armoured fish that hunted Late Devonian seas around 370 million years ago. Instead of teeth, it had sharp, self-sharpening bony plates in its jaws that gave it a very powerful bite.