Peering down on palms, ferns, and a thirsty Uintatherium below, this mural shows how North American mammals moved vertically to take advantage of new Eocene ecological opportunities. The primitive primate Notharctus braces against a branch to pick ripe fruit, which it spotted with its 3D color vision. Besides grasping hands and forward-facing eyes, distinctive primate traits include very flexible forelimbs and a large brain relative to body size. The ancient bat Icaronycteris, among the first of the sole group of mammals that has evolved flight, swerves past in pursuit of insects. Some mammals that couldn’t climb or fly took to digging underground, seeking shelter from predators or temperature extremes.

Grasping hands allowed early primates such as Smilodectes gracilis to climb trees. Their relatively big brains helped with hand-eye coordination, crucial in this new habitat.

The early bat Icaronycteris index ate insects but couldn’t echolocate for them in flight. A long tail and lack of leg membrane were among its many primitive traits.

Living like a modern prairie dog, the plains-dwelling beaver Fossorcastor fossor dug corkscrew-shaped burrows with its incisors and claws. The burrows mystified scientists until beaver skeletons were found inside.