Primal fear

An ancient mammal escapes a snake.
The scene doesn't try to depict a very specific geological period, but heavily leans on fossils from Paleogene (the period right after the extinction of the dinosaurs). The inspiration for the mammal is Purgatorius, which is thought to be one of those groups that could be closely related to our very distant ancestors. Many mammals during the Jurassic, Cretacious, and Paleogene had this type of morphology. We have a very poor record of snakes... but gene sequencing suggests they were around for a looong period of time, and hunted our mammalian ancestors.
This particular snake is a proto-python, with distinct thermal pits. The first thermal pits were found in fossils from Paleogene. However, given that python and vipers (related lineages that both have thermal senses) split somewhere in the Mezozoic, it wouldn't be surprising if snakes were smashing our distant furry relatives even when dinosaurs were still walking.
The environment flora leans on the Mezozoic side.