Spinosaurus

The Spinosaurus is a three-part fossil that can be donated to the museum in Animal Crossing: New Leaf.

Completing the Sabretooth in New Leaf
In New Leaf, a plaque by the display offers information about the fossil instead of Blathers.

"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."