Stegosaur

The Stegosaur is a three-part fossil that can be donated to the museum in all games to date.

In Animal Crossing
"Finally! The day has come! Our stegosaurus is complete! Dare I believe it? Might this not be some cruel dream? Nay, it is true, indeed! I say to you: HOOOO! Spectacular! Superb! My whole being thrills! Now then, where to begin? Much has been written about the noble stegosaurus... It was the largest of the plated dinosaurs, and lived during the late Jurassic period, wot wot. It is famous for the two rows of alternating, bony plates surmounting its body and its four formidable tail spikes. Ka-smash! Yes, that’s correct. It’s a tail-spike chop! Oh... Please pardon me! I was overcome with emotion."

In Wild World
"It emerged right around the middle of the era when dinosaurs roamed the earth. The diamond-shaped plates embedded along its back are actually made of bone, wot? Indeed, they were used to keep it cool and also to thwart its enemies. Ah. Hoo. Indeed, so sorry. Stegosaurs never fail to set my beak blabbing!"

In City Folk
"...It is done! Hootie hoo, the stegosaurus is all done! Absolutely spectacular! The stegosaurus appeared in the middle of the days of the dinosaurs. Its defining characteristics were the plates extending out of its back. These were actually bones, eh wot? They were used to regulate the beastie's body temperature, much as an elephant uses its ears. Its brain was so small, if you stomped its tail, it would not feel it for some time! Or so they say. HOO! I...beg your pardon! I was so enthralled I...I spouted hot air like a boiling teapot, eh wot?"

In New Leaf
"The name stegosaurus literally means "roofed lizard" or "covered lizard." This name came from a belief at the time of discovery that it was covered in bony plates like a shell. We now know that the plates stood fully upright along its back and were covered in thick skin. Beyond protection from harm, they were likely used to regulate body temperature."