The Cretaceous Creekbed diorama is in the "Prehistoric Journey" exhibition on the 3rd Floor.  There's an elf riding a dinosaur in this exhibit.

The Cretaceous Creekbed diorama. Un-zoomed.  The elf is painted on the wall of the diorama, to the left of the fighting bony-headed dinosaurs.

The elf is painted on the left wall of the diorama.  He's waving while riding the dinosaur. He has a light green outfit and brown hat.

Closeup