China Had Owls That Were Active In The Daytime. Study Finds First Fossils Of The Extinct Species

The scientists discovered the fossil skeletons between rocks deposited during the late Miocene Epoch, at an elevation greater than 2,100 metres, in the Linxia Basin of China's Gansu province.

New Delhi: An international team of researchers has discovered the amazingly well-preserved fossil skeleton of an extinct owl that lived more than six million years ago in China. The owl was active in the daytime, and not at night, the skeleton's fossilised eyes bones indicate. 

The study, led by researchers at the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences, was recently published in the journal Proceedings of the National Academy of Sciences (PNAS). 

Where Was The Fossil Found?

The scientists discovered the fossil skeletons between rocks deposited during the late Miocene Epoch, at an elevation greater than 2,100 metres, in the Linxia Basin of China's Gansu province, located at the edge of the Tibetan Plateau. 

How Well Is The Fossil Preserved?

According to the study, nearly the entire skeleton, from the tip of the skull through the wings and legs to the tailbone, is preserved in the fossil. It has also preserved body parts that are rarely seen in fossils. These include the bones of the tongue apparatus called the hyoid, the trachea, the kneecap, tendons for wing and leg muscles, and even the remnants of the owl's last meal of a small mammal.

First Record Of An Ancient Owl Being Diurnal

According to the study, this extinct species is the first record of an ancient owl being diurnal, or active during the day. The diurnal Northern Hawk Owl (Surnia ulula) is a close living relative of the owl species whose fossil has been discovered. Therefore, the extinct species has been named Miosurnia diurna in reference to its close living relative.

The researchers inferred that Miosurnia is a part of the global owl group Surniini by studying the features of the skull and skeleton, including a large bump on part of the cheekbone just behind the eye. Miosurnia is the extinct genus of Surniini group from the Late Miocene. Miosurnia diurna is the only species belonging to the genus. 

The findings show that the Surniini, which includes Miosurnia, the Northern Hawk Owl, and the pygmy owls, rejected the night millions of years ago, the study said.

Owls are largely nocturnal animals. However, a few species are actually largely diurnal.

How Did The Researchers Determine The Owl Is Diurnal?

Dr Li Zhiheng, the first author of the study, said in a statement issued by the Chinese Academy of Sciences that it is the amazing preservation of the bones of the eye in this fossil skull that allows the researchers to see that this owl preferred the day and not the night. 

Small bones that form a ring around the pupil and iris in the other region of the eye are called scleral bones. In order to see in low-light conditions, nocturnal animals require overall larger eyes and bigger pupils. However, diurnal animals have smaller eyes and pupils.

The soft parts of the eye in the Miosurnia diurna fossil had decayed long ago, the study said. As a result, the small trapezoidal scleral ossicles were left randomly collapsed onto the owl's eye socket. 

It is because of this reason that the palaeontologists had to measure the individual small bones and do some basic geometry to rebuild the size and shape of the ring around the eye, the study said.

Dr Thomas Stidham said it was a bit like "playing with Lego blocks, just digitally." He described how the 16 little similar bones overlap each other to form a ring around the iris and pupil. 

The researchers compared the fossil owl's scleral ossicles with the eyes of 55 species of reptiles and more than 360 species of birds, including many owls. 

The scientists observed the size and shape of the fossil's eyes, and found that it has a relatively smaller opening for light. On the basis of these factors, they determined that the extinct owl's eyes most resemble the eyes of living owls in the Surniini group, which is largely not nocturnal.

Using behavioural data from more than 360 species across a diversity of birds, the researchers performed an ancestral state reconstruction, wherein they used the avian family tree to reconstruct ancestral habits of birds, including owls. They did so to determine which owls were likely nocturnal or diurnal.

The study authors found that the ancestor of all living owls was almost certainly nocturnal. However, the ancestor of the Surniini group was diurnal. 

The scientists also added the Miosurnia diurna fossil into the statistical analysis. On doing so, the probability that the ancestor of Surniini was diurnal increased to 100 per cent. Therefore, findings about the behaviour and the eyes point to the evolution of diurnal behaviour in the Surniini owl group. 

According to the statement, Dr Stidham said that Miosurnia diurna is the first record of an evolutionary process spanning millions of years. He said that owls evolved to "reject the night for some fun in the sun."