Modern birds live in almost all habitats on Earth, and only a few birds are adaptable, allowing them to prey on active prey at night. Birds are derived from a group of dinosaurs known as theropods. Scientists have long wondered whether any of the ancient dinosaurs had the sensory adaptations that allowed them to hunt at night. A new study led by Professor Jonah Choiniere of the University of Witwatersrand has answered this question.
Choiniere and his team investigated how the visual and auditory abilities of dinosaurs and birds were compared. The researchers used CT scans 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 pinna, which is an organ that processes incoming sound information, similar to the cochlea of mammals.
One modern bird capable of hunting in complete darkness is the barn owl. Barn owls can hunt with hearing alone and have the largest pinna of all birds. The researchers assessed vision by looking at the scleral ring, a series of bones that surround the pupil of each species. The more the pupils open, the more light can enter, and the better the bird's vision at night. In this way, measuring the diameter of the ring allows scientists to determine how much light can be concentrated in the eye.
Over the course of the study, the team found that many carnivorous carnivores like Tyrannosaurus had optimized vision during the day and had better than average hearing. The team also found that a small theropod called Shuvuui had extraordinary hearing and night vision abilities. The species has a very large pinna, almost identical in relative size to the modern barn owl.
The discovery suggests that like barn owls, Shuvuui can hunt in complete darkness. The creature, which has long since ceased to appear in the world, also has a striking pair of eyes, said to be the largest proportion of pupils measured in birds or dinosaurs, suggesting that they could also see very clearly at night. Shuvuui was about the size of a chicken and lived in the desert of what is now Mongolia.
