Lars Schmitz is a Scripps College associate professor of biology. Jonah Choiniere is a University of the Witwatersrand professor of dinosaur paleontology, and Roger Benson is a University of Oxford professor of Palaeobiology. This article first appeared on Conversation.
Barn owls, bats, leopards, and various other species rely on their acute senses to survive and search in the dark. These nighttime hunters escape the crowds of daytime hours by stalking their targets in the snow, often using a mixture of night vision and keen hearing.
But, 100 million years ago, did there exist nightlife? Were dinosaurs working the night shift in a world without owls or leopards? If that’s the case, what senses did they use in the dark to locate food and escape predators? To have a greater understanding of the senses of birds’ dinosaur ancestors, Paleontologists and paleobiologists combed through scientific papers and museum archives for fossils of the intact fragile eye and ear systems. We discovered a few.
We describe the most compelling evidence for nocturnal dinosaurs to date, using scans of fossilized dinosaur skulls, on a paper published in the science journal on May 6, 2021. Haplocheirus Sollers and Shuvuuia deserti, two extinct animals, had excellent night vision. But, like modern-day owls, S. deserti had sensitive ears, according to our findings. This is the first time these two characteristics have been discovered together in the same fossil. This implies that this primitive, desert-dwelling dinosaur from ancient Mongolia was most likely a specialist night-hunter of insects and small mammals.
Shuvuuia deserti possessed excellent hearing and low-light vision, allowing it to hunt at night.
Taking a look at theropods
Lars Schmitz, one of us, had previously discovered that certain small predatory dinosaurs might have killed at night by examining fossilized eye bones. Theropods, a group of three-toed dinosaurs that comprises Tyrannosaurus rex and modern birds, made up most of these possibly nocturnal hunters. However, only 12 theropod species have had their eye systems preserved in fossils, which may teach paleontologists a lot about the vision at night.
For a total of 16, our team discovered four more theropod species with hints to their sense of vision. We then searched for fossils that preserved the inner ear systems and found 17 organisms. We were able to get measures for both eyes and ears for four animals, which was exciting.
The bones in your eyes were designed to help you see in the dark.
Scleral ossicles are small rectangular bone plates that form a ring-like structure around the eyes of lizards, birds, and dinosaurs. The maximum possible size of an animal’s pupil is described by scleral rings, which will tell you how much the animal sees at night. The bigger the pupil in comparison to the size of the eye, the greater a dinosaur’s night vision.
Our team scanned the bones and then digitally rebuilt the eyes since the human bony ossicles of these rings fell apart when these creatures died more than 60 million years ago. H. Sollers and S. deserti had some of the most prominent pupils compared to their size among the theropods we studied.
S. deserti had a pupil that took up more than half of the eye, equivalent to modern-day night-vision experts like geckos and nightjars. The fossils were then compared to 55 live lizard species and 367 living bird species with established day and night behavior patterns. According to our team’s statistical analyses, there’s an excellent probability that H. Sollers and S. deserti were nocturnal (more than 90%).
However, those were not the only two theropods that our team studied. Other possible nighttime specialists, such as Megapnosaurus kayentakatae and daytime specialists, such as Almas ukhaa, were discovered during our research. However, certain animals, such as Velociraptor mongoliensis, had eyesight that seemed to be adapted to medium light conditions. This may indicate that they hunted at dawn or dusk.
The inner ear canal molds of a barn owl (left) and S. deserti (right) are almost similar, implying that the tiny dinosaur had exceptional hearing.
Incredible dinosaur ears
Hearing is almost as necessary as a vision in today’s nocturnal animals. We scanned the skulls of 17 fossil theropods to discern the anatomy of their inner ears and compared our analyses to the ears of modern animals to see how much they could hear.
The cochlea is a tube-like canal deep inside the inner ear of all vertebrates. The deeper this canal is, the greater the range of frequencies an animal can detect and the more they can hear very faint sounds, according to studies of live mammals and birds.
S. deserti had an unusually long inner ear canal for its size, comparable to that of a live barn owl and proportionally much longer than any of the other 88 living bird species we compared it to. We discovered that predators have more excellent hearing than herbivores based on our calculations. Several predators had relatively elongated inner ears, like V. mongoliensis, but none matched S. deserti’s.
A nocturnal dinosaur’s day-to-day life
Paleontologists like us can discover not only what animals roamed the night by observing dinosaur sensing skills, but we can also infer how these dinosaurs lived and exchanged resources.
S. deserti had exceptional night vision and hearing, and it was likely that this small dinosaur used its extraordinary senses to capture prey at night. It will probably hear and watch rustling from afar before visually finding its prey and picking it up with its small single-clawed arms from the dirt. It could have been an evolutionary benefit to be involved in the colder temperatures of the night in the harsh, desert-like environments of millions of years ago.
However, S. deserti wasn’t the only dinosaur alive at night, according to our findings. Other dinosaurs with night vision, such as V. mongoliensis and the plant-eating Protoceratops mongoliensis, shared the same habitat.
Paleontologists don’t know the full range of species that shared S. deserti’s harsh nocturnal lifestyle in Mongolia’s ancient deserts. Finding fossils with the right bones preserved, which allows paleontologists to explore their senses, is difficult. The presence of a specialized night forager, on the other hand, emphasizes that, just as today, Any dinosaurs roamed under the stars, avoiding the hazards and competition of daytime hours.