Primitive horses and tapirs found shelter in the thickets overgrown with ferns and climbing plants. Giant squirrels leaped through the treetops and monkeys played in the branches. Crocodiles lurked in the fish-rich lakes lined with steep banks. At night, bats went hunting. Insects and arachnids found favorable conditions everywhere. The Eocene was one of the warmest periods in the history of the Earth. The Earth was almost ice-free and the sea level was several meters higher than today.

The tree population around the volcanic lakes resembled that of today's tropical and subtropical regions. In addition to numerous walnut, elm, and rose plants, palm, laurel, and tea plants also thrived. Conifers were less common. In the shade of the tree crowns, dense undergrowth of herbaceous plants and ferns grew rampant. Climbing plants, such as vines and climbing ferns, wound their way up into the branches of the trees.