Dinosaurs were active both day and night, study claims

Some dinosaurs did their hunting at night, new research suggests.

Studies of the eyes of existing birds and reptiles with different daily activity patterns were compared with similar parts in dinosaur fossils.

The results suggests that small, meat-eating dinosaurs were nocturnal; large, plant-eating dinosaurs tended to forage both during the day and at night.

The Science study also challenges the notion that mammals' nocturnal nature evolved to avoid day-active dinosaurs.
Lars Schmitz and Ryosuke Motani of the University of California Davis have been looking at the eye parts of dinosaurs, and their modern-day descendants the lizards and birds, for a number of years.

They have been trying to determine just how big and how light-sensitive dinosaurs' eyes would have been.
That in turn would be an indication of whether they were active at night; until now the assumption has been that dinosaurs were diurnal, or primarily active in the daytime only.

However, fossils give no indication of how large dinosaurs' pupils would have been - an indication of how much light they could gather up, and thus of whether they were nocturnal "night stalkers".