Trilobite

Trilobite 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 1,300 Bells.

Trilobites were sea-dwelling arthropods that thrived for around 270 million years before dying out about 252 million years ago. They were among the first animals with complex eyes, built from crystal lenses.