Archelon

The Archelon is a two-part fossil that can be donated to the museum in and.

In New Leaf
"With a name that literally means "ruler turtle," the archelon was an ancient species of sea turtle. Reaching 13 feet in length and two metric tons in weight, it was a giant that lived up to its name. It likely ate jellyfish and squid, though theories say it may have also preyed on ammonites. Unlike with modern turtles, its shell was too soft to allow it to pull in its limbs for a defensive position."

In New Horizons
"Ah yes. Archelon. It was a sort of huge sea turtle. The largest thus far found, if you want to know. They were very sizable-some 13 feet long, with a shell the size of a small car... If you're into that sort of thing. They likely ate seaweed, shrimp, octopus, and possibly ammonites, given the era involved. It seems CERTAIN giant turtles had to be prima donnas and eat some of the oldest life forms on earth!"

In Real Life
Archelon was a herbivorous marine turtle from the Late Cretaceous period. It is the largest turtle ever known, at up to 4.6 meters in length and weighing up to 2200 kg. It had not a solid shell, but a leathery one supported by a skeletal framework. It lived in the Western Interior Seaway, which went down the middle of modern-day North America, from 80 to 71 million years ago.