Researchers in the United States say meat-eating dinosaurs used night vision to track down their prey - a finding which challenges the theory that carnivorous dinosaurs were daytime hunters.
The findings, published in the journal Science came from researchers at the University of California.
They first measured the size of the eye socket and a bone in the eye region called the scleral ring in existing birds and reptiles and correlated these with the times these creatures were most active.
The BBC reports they then applied their findings to 33 dinosaur fossils and the results suggest that small, meat-eating dinosaurs such as velociraptor were nocturnal while large, plant-eating dinosaurs were active day and night.
The researchers believe that is because these giants needed to constantly forage to maintain they needed to constantly forage to maintain their size.
As well as countering the assumption until now that dinosaurs were primarily active only during the day, the new research also challenges the notion that mammals evolved nocturnal habits to avoid day-active dinosaurs.