 Mesopic vision is characteristic of cathemeral animals, which are active in both night and day, and crepuscular animals, which are active in twilight.Adaptations to see in dim light may have been ancestral to archosaurs, and "Proterosuchus" may have been an early example of this trend.However, "Proterosuchus" lived near the Antarctic Circle, so its mesopic vision may have instead been an adaptation to the highly seasonal day lengths it experienced.