The nocturnal species are the species that are active during the night, while during the day they rest, sleep, or hide. The life in the darkness has made these species develop some features that are common for almost all of them, despite them being in different families. The features that are mostly found at these species are the very well developed sense of smell, hearing, and enlarged and well developed eyes. When looking at fossil remains of such species, thy can easily be defined as nocturnal by the professionals, as they will exhibit larger and more developed nasal cavities, the ear bones will be larger and better developed, and the eye cavities will also be very large, usually proportionally larger than what they are in the diurnal species.