Acanthostega

The acanthostega is a stand-alone fossil that can be donated to the museum in.

Real-world information
Acanthostega gunnari was an animal from the late Devonian period and is representative of the evolution of tetrapods, or land vertebrates. While not well suited for life on land, it nevertheless exhibits important evolutionary advances in that direction. Notably, its locomotion was powered by its back fins instead of its front.