Mesozoic
Textbooks have always described how the Mesozoic was the age of the dinosaurs, which has even more sense now that we know birds descended from land dinosaurs. It was the age, too, of extraordinary marine reptiles. Mammals were mainly small nocturnal animals which scurried around in the night-times of the great forests. We know from their loss of color vision (which is trichromatic in fish and reptiles) that mammals lived a nocturnal life.