Spinosaurus

The Spinosaurus is a three-part fossil that can be donated by the player to the museum in and.

Completing the Spinosaurus in New Leaf
"The spinosaurus is famous for the sail on its back, made up of skin stretched over spikelike bones. The assumption is that these sails were used to help regulate body temperature, common for reptiles. In addition to having this large sail, it is also the largest of the carnivorous dinosaurs. Despite being so commanding, its diet most likely consisted of fish from swampy, marshy regions."

In New Horizons
"Ahem. Yes. The Spinosaurus was a very large, carnivorous dinosaur, roughly the size of a T. Rex. Unlike its more famous cousin, however, Spinosaurus seems to have spent a great deal of time in water. Similar to modern crocodiles, this creature lived on a diet of fish AND land-dwelling animals. Personally, I am simply relieved that it did not seek FLYING prey."

In Real Life
Spinosaurus lived in what is now North Africa and weighed on average 14,000 kilograms. There were up to 6 species of spinosaurus. It was a carnivore.