Dinosaurs were active both day and night

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. ...

we saw pretty much everything: we had diurnal, nocturnal and species active both day and night, that was the first surprise," Dr Schmitz said.

"The activity patterns depend essentially on what they do for a living - what the ecology is. Small carnivores like velociraptor tended to be nocturnal or active day and night; we didn't have a diurnal carnivore in our analysis.

"Large herbivores, they were almost exclusively day- and night-active."

Dr Schmitz said this was probably because larger animals needed to forage longer to support their large sizes.

The find also casts doubt on the idea that mammals - who in modern times are predominantly nocturnal - evolved their activity patterns to avoid being targeted by day-active dinosaurs.

"We now know that dinosaurs were active at night as well, so the whole story is much more complicated," Dr Schmitz said. ...

via BBC News - Dinosaurs were active both day and night, study claims.