‘Strange bird’ specimen might have looked like any other bird 120 million years ago — until it opened its mouth

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A peculiar fossil has helped scientists discover an unusual bird that lived among the dinosaurs 120 million years ago, and the find is changing the way researchers think about avian evolution.

The previously unknown species has been named Imparavis attenboroughi, which means “Attenborough’s strange bird” in Latin in honor of British naturalist Sir David Attenborough.

All birds descended from dinosaurs, and some of the earliest ones resembled them. But Imparavis, which belonged to a diverse bird group called enantiornithines, likely looked more like the birds we’re familiar with today, according to a new study published Tuesday in the journal Cretaceous Research.

Enantiornithines are known as “opposite birds” because they had a shoulder joint feature that greatly differs from the ones modern birds have.

“Enantiornithines are very weird. Most of them had teeth and still had clawed digits,” said lead study author Alex Clark, a doctoral student at the University of Chicago and the Field Museum of Natural History, in a statement. “If you were to go back in time 120 million years in northeastern China and walk around, you might have seen something that looked like a robin or a cardinal, but then it would open its mouth, and it would be filled with teeth, and it would raise its wing, and you would realize that it had little fingers.”

But Imparavis was the first known bird of its kind to be toothless in a landscape full of birds with teeth, according to the study.

“Before Imparavis, toothlessness in this group of birds was known to occur around 70 million years ago,” Clark said. “With Imparavis, it turns out it occurred nearly 48 million years earlier. Today, all birds lack teeth. But back in the Mesozoic, toothed little mouths were the norm. If you saw one without teeth, it’d be the oddball — and that’s what Imparavis was.”

Finding a strange fossil

The fossil was first discovered by an amateur collector near northeastern China’s Toudaoyingzi village and donated to the Shandong Pingyi Tianyu Natural Museum. When Jingmai O’Connor, the Field Museum’s associate curator of fossil reptiles, visited the Shandong museum’s collections a few years ago, the fossil caught her attention.

“I think what drew me to the specimen wasn’t its lack of teeth — it was its forelimbs,” said study coauthor O’Connor, who is also Clark’s adviser, in a statement. “It had a giant bicipital crest — a bony process jutting out at the top of the upper arm bone, where muscles attach. I’d seen crests like that in Late Cretaceous birds, but not in the Early Cretaceous like this one. That’s when I first suspected it might be a new species.”

Clark, O’Connor and their colleagues began studying the fossil in early 2023, and they were surprised by the bird’s lack of teeth in addition to its unu sual forelimbs, or wing bones.

Imparavis had large attachment points for muscles in its wing bones, suggesting it could generate a lot of power with its wings and had a strong downward wing beat, kind of like doing a massive aerial push-up, Clark said.

“We’re potentially looking at really strong wing beats. Some features of the bones resemble those of modern birds like puffins or murres, which can flap crazy fast, or quails and pheasants, which are stout little birds but produce enough power to launch nearly vertically at a moment’s notice when threatened,” Clark said.

While modern birds have fused forelimb digits, enantiornithines still had independent movement in the “little fingers” on their wings.

“Most of the ‘hand’ would be encased in tissue to help form the wing, but the little claws (and yes they did have little claws) might have been used to manipulate food, aid in climbing, or other yet-not-thought-of behaviors,” Clark said.

The mysteries of avian evolution

Clark and his colleagues can’t say for sure what kind of foods Imparavis ate or exactly why it was toothless. Features of the bird’s hind limbs suggest it likely foraged on the forest floor, perhaps in search of fruits, seeds or insects.

The bird, like other enantiornithines, didn’t have a digestive organ called a gizzard that helps modern birds crush up their food for easier digestion, “so the evolutionary pressures that led to toothlessness in other groups of dinosaurs were likely not the same ones for enantiornithines like Imparavis,” Clark said.

As other birds lost their teeth over time, they would ingest stomach stones to create a gastric mill to help crush the food they ate. But Imparavis didn’t behave that way. Until the scientists find more examples of Imparavis, the mystery of what the bird ate and how it digested food remains.

Imparavis could likely be seen hopping and walking on the ground like modern robins, Clark said.

“It seems like most enantiornithines were pretty arboreal, but the differences in the forelimb structure of Imparavis suggests that even though it still probably lived in the trees, it maybe ventured down to the ground to feed, and that might mean it had a unique diet compared to other enantiornithines, which also might explain why it lost its teeth,” O’Connor said.

One of the key remaining questions among researchers about bird evolution is why the more diverse enantiornithines went extinct 66 million years ago along with the dinosaurs, while another group called ornithuromorphs survived and enabled modern birds to evolve.

“Some have thought maybe it was because ornithuromorphs were more commonly associated with water/river systems, others have thought maybe different metabolisms, and others still perhaps differences in nesting or rearing young,” Clark said in the statement. “This is where more fossil specimens and more statistical models will come into play in the future — so stay tuned!”

Understanding extinct species

Clark is currently researching new specimens that showcase both the surprising similarities and differences between ancient and modern birds, revealing what “little paradoxical creatures” they can be.

Clark credits his interest in the natural sciences to watching Attenborough’s nature documentaries, hence the name of the new fossil.

“It is a great honour to have one’s name attached to a fossil, particularly one as spectacular and important as this. It seems the history of birds is more complex than we knew,” Attenborough said in a statement.

But studying extinct animals doesn’t just shed light on the past — it also raises awareness for the future, according to the researchers.

“Learning about enantiornithines like Imparavis attenboroughi helps us understand why they went extinct and why modern birds survived, which is really important for understanding the sixth mass extinction that we’re in now,” O’Connor said. “The biggest crisis humanity is facing is the sixth mass extinction, and paleontology provides the only evidence we have for how organisms respond to environmental changes and how animals respond to the stress of other organisms going extinct.”

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