March 28th

Dinosaurs in the Dark

They’re terrifying enough in broad daylight, but were some dinosaurs nocturnal? A study in 2011 tried to answer that question, which seemed like a riddle that couldn’t be answered through skeletal data. That is, until scientists started looking into dinosaur eyes.

Unlike mammals, archosaurs (a group that includes dinosaurs, along with crocodiles and birds) have a ring of bone in their eye sockets called the scleral ring. This gives an indication of the size of a dinosaur’s eye. Since fossilized soft tissue is rarely found, scleral rings give us a window into Mesozoic irises.

Velociraptor / Wikimedia Commons


The size of an animal’s eyes can provide clues to its habits. Modern animals with large eyes often live in low-light environments or have adopted a nocturnal lifestyle. Larger eyes capture more light, which makes seeing in the dark easier. Examining modern nocturnal animals, scientists found that a large pupil in relation to the retina was indicative of operating in dark conditions. Using the scleral rings to determine the size of the eye in relation to a dinosaur’s eye socket, scientists hoped to determine whether the ancient creatures could operate at night. So were dinosaurs confined to the daylight?

Research suggests that they might not have been restricted to living in the sunshine. Comparing 33 Mesozoic archosaur species with 1401 living species from many animal groups revealed that dinosaurs were not uniform in their optical equipment. Based on this data, researchers concluded that animals like Velociraptor and Microraptor could have been partially nocturnal. Psittacosaurus and the giant Diplodocus seemed ready for both day and night time behaviors, like many of today’s animals.

Whether these conclusions are accurate or merely plausible, the idea of packs of raptors hunting in the darkness is bone-chilling.

Share your fascinations and fears about nocturnal dinosaurs with us on Facebook and Twitter using the hashtag #TDIDinos.