As all modern birds are the direct descendents of theropod dinosaurs, such as velociraptors and the mighty T-rex, for a long time scientists have wondered whether any relatives of these formidable hunters had the ability to stalk their prey in the dead of night.
The answer is yes, though unlike the massive meat-eating power-houses mentioned above, the species identified as having the necessary biology is very small and much less ferocious in appearance.
Meet the shuvuuia, a member of a group of dinosaurs known as alvarezsaurs, which had both extraordinary hearing and night vision.
The extremely large ear bones of this species suggest that the shuvuuia could have hunted in complete darkness, scientists said.
The new study, led by the University of the Witwatersrand’s Professor Jonah Choiniere, 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, the organ that processes incoming sound information, and is called the cochlea in mammals.
The barn owl, which can hunt in complete darkness using hearing alone, has the proportionally longest lagena of any bird.
To assess vision, the team looked at the scleral ring, a series of bones surrounding the pupil, of each species.
They compared this to a camera lens – the larger the pupil can open, the more light can get in, enabling better vision at night.
By measuring the diameter of the ring, the scientists could tell how much light the eye can gather.
The team found that many carnivorous theropods such as the T-rex and dromaeosaurus had vision which was particularly optimised for the daytime, and that they had better-than-average hearing, which they said was presumably to help them hunt.
But the large lagena of shuvuuia came as a surprise discovery to Dr James Neenan, the joint first author of the study.
“As I was digitally reconstructing the shuvuuia skull, I couldn’t believe the lagena size... I called Professor Choiniere to have a look.
“We both thought it might be a mistake, so I processed the other ear – only then did we realise what a cool discovery we had on our hands!” he said.
Professor Choiniere said: “I couldn’t believe what I was seeing when I got there – dinosaur ears weren’t supposed to look like that.”
The eyes of shuvuuia were also of note, as the fossils indicated they had had some of the proportionally largest pupils yet measured in birds or dinosaurs, suggesting that they could likely see very well at night.
Shuvuuia was a small dinosaur, about the size of a chicken, and it lived in the deserts of what is now Mongolia.
The creature’s skeleton is among the most bizarre of all dinosaurs, the researchers said.
It has a fragile, bird-like skull, brawny, weightlifter arms with a single claw on each hand, and long, roadrunner-like legs.
This odd combination of features has baffled scientists since its discovery in the 1990s. But with the new data on shuvuuia’s senses, the scientific team hypothesises that, like many desert animals, Shuvuuia would have foraged at night, using its hearing and vision to find prey like small mammals and insects, using its long legs to rapidly run that prey down, and using its strong forelimbs to pry the prey out of burrows or shrubby vegetation.
“Nocturnal activity, digging ability, and long hind limbs are all features of animals that live in deserts today,” said Professor Choiniere, “but it’s surprising to see them all combined in a single dinosaur species that lived more than 65 million years ago.”
The research is published in the journal Science.