Fossil holds clues to how some owls evolved into daytime hunters

In the silty red soil of Gansu province in China, a small owl has lain nestled for about 6 million years, since an era known as the Late Miocene. The fossilised bird’s talons are outstretched, one of its wings is spread wide, and its sharp beak is turned back over its shoulder.

An analysis of the fossil published in the Proceedings of the National Academy of Science suggests that judging from the size and shape of its eye sockets, the owl hunted under the sun, rather than the moon. The fossil could offer clues into the evolutionary forces that transformed this bird and some other species into the owl equivalent of a morning person.

The fossil owl, an extinct species that the researchers have named Miosurnia diurnal, is exquisitely preserved, said Li Zhiheng, a palaeontologist at the Institute of Vertebrate Palaeontology and Paleoanthropology at the Chinese Academy of Sciences and an author of the new paper. This allowed the team to take precise measurements of its bones. They then fed the bird’s dimensions into a computer programme that made predictions about an organism’s lifestyle, comparing the data with the anatomies of a variety of reptile and bird species.

Many modern owls are nocturnal. The eyes of night owls have many more rod cells than cone cells, allowing them to see better in dim light.

But some of the birds are diurnal, meaning they are active in the daytime. Scientists suspect that these daywalker owls evolved from nocturnal ancestors, meaning that they shifted their period of activity at some point in the past.

The fossil in the new study has elongated eye sockets and rings of bone around the eyes. These shapes resemble those of modern diurnal owls.

If some owls shifted to a diurnal lifestyle as early as 6 million years ago, it may be possible to find clues about what caused them to make this change in what we know about their environment. The part of Gansu province where the fossil was found is near the Tibetan Plateau, and it was likely a cold, harsh place to live, Li said. Perhaps the small mammals that owls preyed on evolved away from nighttime activity to take advantage of warmer temperatures in the day. They would perhaps have drawn their predators, over the aeons, into the light themselves.

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