Juramaia

The Juramaia is a fossil that can be donated to the museum in.

In New Horizons
"Ah, yes, the juramaia: one of the first mammals, and one of the few to live alongside the dinosaurs! In order to hide from much larger dinosaurs, it was less than four inches long and quite unobtrusive. Some even theorize that these mammals were nocturnal until the dinosaurs went extinct. They needed every advantage to live among those behemoths. They were nocturnal before it was cool!"

In Real Life
Juramaia sinensis is one of the earliest known eutherians, or mammals more closely related to placental mammals than marsupials. It lived during the Late Jurassic in northeastern China and shared its habitat with early ancestors of birds, including Anchiornis and Xiaotingia. Juramaia's forelimbs were adapted for climbing, leading some to speculate that early eutherians may have been arboreal.