Pteranodon

The Pteranodon is a fossil that can be donated to the museum in all games to date. It is a three or four-part fossil, depending on the game - introduced a fourth part, the body, which was removed in  but re-introduced in.

In Animal Crossing
"First things first, this winged creature is not actually a dinosaur, but rather a flying reptile. It did, however, live among many dinosaurs during the late Cretaceous period. Fascinating, eh wot? The structure of its immense wings suggests that is stayed aloft by gliding rather than flapping, you see? Imagine pteranodons with wingspans of over 23 feet swooping down to catch fish in their pelican-like beaks...Screee...SCHWAAAH!!! Oh, I do beg your pardon. Beaks, wings, flying...It's so very close to home!"

In
"The pteranodon was simply a wonderful creature. It emerged in the later age of dinosaurs, winging through the ancient skies. Though it could fly, it was most certainly not a bird! No, it was a reptile, wot! When it spread its wings, it was as big as a small airplane. Simply gargantuan! The very thought boggles my brain, to be honest. Ah. Hoo. Yes, so sorry. I'm actually rather glad the brute no longer exists."

In
"Pteranodons were a type of winged reptile, perhaps the ancestors of common birds. With their wings spread, they were about the size of a small airplane, but their bodies were very light. Strangely, they weighed less than 50 pounds, with wings made from skin, allowing for ease of flight."

Real-world information
Pteranodon was a pterosaur which lived 86–84.5 million years ago around the Western Interior Seaway, a shallow sea that stretched down the middle of modern-day North America. Around 1,200 specimens of Pteranodon have been found, more than any other pterosaur. Males had an average wingspan of 5.6 meters, while females averaged 3.8 meters. They were known to have been piscivores, or fish-eaters. In the past, it was believed they could not take off from the water and would have skimmed the surface with its toothless beak (from which it gets its name) while flying. However, more recent studies suggest that not only were they able to land and take off from the water's surface, but they may also have been able to dive for fish.