Nocturnal behavior was once thought to have been evolved with modern mammals. However recent fossil evidence of eye structures of the ancestors of mammals revealed that they preferred a nocturnal existence.
Nocturnal behavior is seen in a lot many modern mammals were evolving much earlier than what is popularly believed. There is irrefutable proof in the fossil records of a group of predecessors of mammals who were known as synapsids and lived some 300 million years ago. This is 100 million years before the first true mammals made their appearance.
A study published in the Proceedings of the Royal Society B reports that little ring-shaped bones known as scleral ossicles were found embedded in the eye sockets of these ancient creatures. The scleral ossicles give researchers a fair idea of the size and shape of different parts of the eye ball and in the process helps them to make predictions about the light sensitivity of the eye. This in turn reveals whether the animal is active nocturnally or in the day time.
The researchers studied the scleral ossicles in species representing major groups of synapsids, finding evidence of considerable differences in light sensitivity. Some of the synapsids had eyes which was adapted for daylight while others had eyes which were better adapted for nocturnal activities.
The presence of nocturnal activities in species so far back in the geological clock shatters much long held belief that nocturnal activity started in the right earnest with the appearance of true mammals. True mammals appeared only some 200 millions ago. It was reasoned that by turning nocturnal mammals were saved from becoming meal of dinosaurs which also inhabited the Earth in that era.
The new findings suggest that belief needs to be reexamined.