As dramatic fossils go, it’s hard to beat the Mongolian fighting dinosaurs – a Velociraptor and a Protoceratops locked in mortal combat. The Protoceratops, an early horned dinosaur, has the raptor’s arm in its mouth, and the raptor appears to be kicking its prey in the neck. The two combatants were killed in this pose, around 75 million years ago. And according to a new study, they probably met and died sometime around dawn or dusk.

Most dinosaur reconstructions portray the animals walking about in bright sunlight but of course, we know that living animals are active at all times of the day. The diurnal ones prefer the daylight hours, while nocturnal species haunt the night. Crepuscular animals favour twilight hours, while cathemeral ones are active in short bursts throughout the day.

It’s easy enough to work out which group a living animal falls into, but the task becomes far more difficult if the animal in question is extinct. With the exception of tracks, burrows or other trace fossils, behaviour doesn’t fossilise easily. But Lars Schmitz and Ryosuke Motani have developed a clever way of working out when ...