Myllokunmingia

The Myllokunmingia is a fossil that can be donated to the museum in.

In New Horizons
When donating to the museum, Blathers will say the following:

"The myllokunmingia! Said to be one of the oldest fish-like animals, it lived well before the dinosaurs. It was about an inch long and seems to have had no lower jaw. It is awe-inspiring imagining such ancient life! There is much we still don't know. We may yet discover even older organisms with even fewer jaws!"