The Miocene Epoch, around 23 to 2.6 million years ago, is known as the age of mammals. It’s when antelope, deer and giraffes appeared across Eurasia. Bears and dogs emerged for the first time, as did hyenas and saber-toothed cats. But the Miocene was about more than just mammals, it was a time when curious birds abounded. And researchers are pausing on an owl, since it had an unusual feature: It hunted by day.
Researchers published in the Proceedings of the National Academy of Sciences (PNAS) have uncovered a “spectacularly” preserved specimen of an owl that lived in the late Miocene, between six and 9.5 million years ago. It’s preserved enough that they can tell it wasn’t nocturnal like most modern-day owls.
“It’s three-dimensionally preserved with most bones still in articulation with one another,” says study co-author Thomas Stidham, a paleoecologist at the Chinese Academy of Sciences. “The fossil preserves the remains of body parts rarely seen, like the rings of the trachea, digestive tract contents and the hyoid or bony part of the tongue. Ossified tendons even show how now decayed muscles were positioned.”
Researchers found the specimen, named Miosurnia diurna, in the Linxia Basin of China's Gansu province, at the edge of the Tibetan Plateau. The bones are still mostly intact, which provides paleontologists a window into a world they rarely see. The owl likely died just after eating and hadn’t fully digested the bones of its last prey. In fact, the specimen still holds the residue of its last meal in its thoracic region.
“We estimate that the owl died within hours after the meal since it had not regurgitated the bones,” says Stidham.
Researchers examined the scleral ossicles, or the bones around the eye, to determine how big its eyes were compared to other species. This revealed that it hunted by day. They restructured the ossicle ring of the owl, and were able to calculate its feeding patterns.
“Eyes used at night require more light and tend to be relatively larger [in owls at least] and have larger pupils to let in more light,” says Stidham. “Furthermore, the closest relatives of this extinct owl are daytime active owls.”
A Window into a New Species
Biologist and author Jonathan Slaght says this species is somewhat of a hybrid between two modern day hunting owls: the pygmy owl and the Northern hawk owl. “It could almost be named the ‘Giant pygmy owl,’” he says.
The specimen is a big deal because well-preserved avian fossils are uncommon — their delicate bones are hollow and often scatter after the bird’s death, says Slaght. A specimen like this doesn’t happen often. “This is a noteworthy find because so much of the owl skeleton was preserved — enough to identify it as a diurnal species,” says Slaght.
Additionally, the study provides information into the way owls might have lived millions of years ago, which might be different from the way they live today, he says. Most owls today are nocturnal, though some, like snowy owls, burrowing owls and great gray owls, hunt during the day and night. But it doesn’t mean it was always this way, he says.
“An absence of birds in the fossil record can skew our understanding of historical populations. We automatically assume owls are nocturnal because most of them now are. This discovery hints at the past importance of day-hunting owls in open landscapes of Asia: They may have been the rule, rather than the exception,” says Slaght.
Researchers think that the owl may have evolved to hunt by day as its population expanded. “Non-nocturnal habits may be linked to steppe habitat expansion and climatic cooling in the late Miocene,” writes the study’s authors.
Still, this discovery presents as many questions as it does answers. Was day-hunting common for owls during the Miocene and if it was, then why are most of the owls that live today nocturnal? It’s why study author Tom Stidham is on a mission to unlock the mysteries of these owls and other primordial birds of prey.