Triceratops

The Triceratops is a three-part fossil in the introduced in  that has appeared in all subsequent entries to date.

In
When donating the final part to Blathers in, he will provide the following information about the fossil:

"Well now, if I'm not mistaken, I do believe this means... triceratops is complete! Hoo-WEE! Er, did I just say 'hoo-wee'? Ugh. How terribly embarrassing. I sound like some blithering idiot. Let's move on, shall we? Here now... Where to begin? Triceratops... Yes... A member of the ornithischian order, this great beast flourished in the late Cretaceous period. It was a huge three-horned plant-eater, and grew up to 30 feet in length. That's 9 meters! Truly remarkable! Triceratops is easily recognized by its distinctive trio of horns, and, of course, its parrot-like beak. Oh, and one mustn't forget the solid neck frill which provided it with fortification against giant predators. Triceratops was quite formidable indeed. In fact, it was one of the very last dinosaurs to suffer extinction. Oh, dear! Oh good gracious! Please, please forgive me. I tend to get a bit carried away. Dinosaurs, you know!"

In
When donating to Blathers in, he will provide the following information about the fossil:

"Hoo! Indeed, hootie HOO hoo! I'm simply awash in joy! Allow me to compose myself and tell you about the mighty triceratops. This herbivore was one of the last remaining dinosaurs, eh wot? This quiet giant is esily recognized by its three horns and its large collar. The bone in that collar was designed to build more muscles in the neck... Yes, as a result, the biting power of this creature was something to behold! Ah. Hoo. Yes, so sorry. I didn't behold it MYSELF, of course... Hoo."

The Triceratops can be found in the first room of the fossil exhibit in the museum. If the player interacts with the plaque on the fossil, it reads:

"Triceratops Length: 31.2 feet Late Cretaceous"

In
When donating the final part to Blathers in, he will provide the following information about the fossil:

"...Stunning! The triceratops is done! Hoo, naught could make me happier! The triceratops was an herbivorous dino that lived until the end of the days of the dinosaurs. Its distinctive three horns and large collar belied its quiet nature. In actuality, the collarbone was the source of the beastie's mighty chewing power... But with powerful jaws like that, plus the horns, no carnivorous dino wanted a triceratops at its feet! HOO! I...beg your pardon! I was so enthralled, I... I spouted hot air like a boiling teapot, eh wot?"

In
After donating the final part of the fossil in, its plaque in the museum will read:

"The triceratops was a very large herbivore, commonly identified by its three horns and large bone frill. Its horns were likely used for turf wars and fighting over females rather than for protection. While it's true that it most likely lived in the same era as the T.rex, the two probably didn't fight much."

Real-world information
Triceratops was a ceratopsid dinosaur that lived in modern-day North America at the very end of the Cretaceous, 68 to 66 million years ago. It reached up to 9 meters in length and weighed up to 12 tons. Triceratops is named for its three characteristic horns, with a smaller one on the nose and a larger one above each eye. It possessed an unusually short frill, compared to its close relatives in the group Chasmosaurinae. While the horns were traditionally thought to be used for defense, more recent studies have suggested that they were used for species identification and courtship/dominance displays, much like the antlers on modern deer.