Modern birds live in just about every habitat on the planet, with only a few having adaptations allowing them to hunt active prey at night. Birds are derived from a group of dinosaurs known as theropods. Scientists have long wondered if any of the ancient dinosaurs had sensory adaptations allowing them to hunt at night. A new study led by Professor Jonah Choiniere from the University of the Witwatersrand has answered that question.
Choiniere and his team investigated how the vision and hearing abilities of dinosaurs and birds compared. The researchers used CT scanning and detailed measurements to collect information on the relative size of the eyes and inner ears of nearly 100 living bird and extinct dinosaur species. To measure hearing, the team measured the length of the lagena, which is the organ that processes incoming sound information similar to the cochlea in mammals.
One modern bird able to hunt in complete darkness is the barn owl. The owl can hunt using hearing alone and has the largest lagena proportionately of any bird. Researchers looked at the scleral ring to assess vision, which is a series of bones that surrounds the pupil of each species. The larger the pupil can open, the more light can get in and the better vision the bird has at night. Measuring the diameter of the ring allowed scientists to determine how much light could gather in the eye.
During the study, the team found that many carnivorous theropods like the Tyrannosaurus had vision optimized for daytime and better-than-average hearing. The team also discovered that a small theropod called Shuvuui had extraordinary hearing and night vision. The species had an extremely large lagena, almost identical in relative size to the modern barn owl.
The finding suggests that, like the barn owl, the Shuvuui could hunt in complete darkness. The creature also had notable eyes said to be some of the proportionately largest pupils measured in birds or dinosaurs, suggesting they could see very well at night. Shuvuui was about the size of a chicken and lived in the deserts of what is now Mongolia.