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 鈥淎ttenborough鈥檚 strange bird鈥� 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鈥檙e familiar with today, according to a new study published Tuesday in the journal Cretaceous Research.
Enantiornithines are known as 鈥渙pposite birds鈥� because they had a shoulder joint feature that greatly differs from the ones modern birds have.
鈥淓nantiornithines are very weird. Most of them had teeth and still had clawed digits,鈥� said lead study author Alex Clark, a doctoral student at the University of Chicago and the Field Museum 锘縪f Natural History, in a statement. 鈥淚f 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.鈥�
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.
鈥淏efore Imparavis, toothlessness in this group of birds was known to occur around 70 million years ago,鈥� Clark said. 鈥淲ith 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鈥檇 be the oddball 鈥� and that鈥檚 what Imparavis was.鈥�
Finding a strange fossil
The fossil was first discovered by an amateur collector near northeastern China鈥檚 Toudaoyingzi village and donated to the Shandong Pingyi Tianyu Natural Museum. When Jingmai O鈥機onnor, the Field Museum鈥檚 associate curator of fossil reptiles, visited the Shandong museum鈥檚 collections a few years ago, the fossil caught her attention.
鈥淚 think what drew me to the specimen wasn鈥檛 its lack of teeth 鈥� it was its forelimbs,鈥� said study coauthor O鈥機onnor, who is also Clark鈥檚 adviser, in a statement. 鈥淚t had a giant bicipital crest 鈥� a bony process jutting out at the top of the upper arm bone, where muscles attach. I鈥檇 seen crests like that in Late Cretaceous birds, but not in the Early Cretaceous like this one. That鈥檚 when I first suspected it might be a new species.鈥�
Clark, O鈥機onnor and their colleagues began studying the fossil in early 2023, and they were surprised by the bird鈥檚 lack of teeth in addition to its unu锘縮ual 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.
鈥淲e鈥檙e 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鈥檚 notice when threatened,鈥� Clark said.
While modern birds have fused forelimb digits, enantiornithines still had independent movement in the 鈥渓ittle fingers鈥� on their wings.
鈥淢ost of the 鈥榟and鈥� 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,鈥� Clark said.
The mysteries of avian evolution
Clark and his colleagues can鈥檛 say for sure what kind of foods Imparavis ate or exactly why it was toothless. Features of the bird鈥檚 hind limbs suggest it likely foraged on the forest floor, perhaps in search of fruits, seeds or insects.
The bird, like other enantiornithines, didn鈥檛 have a digestive organ called a gizzard that helps modern birds crush up their food for easier digestion, 鈥渟o the evolutionary pressures that led to toothlessness in other groups of dinosaurs were likely not the same ones for enantiornithines like Imparavis,鈥� 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鈥檛 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.
鈥淚t 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,鈥� O鈥機onnor 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.
鈥淪ome 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,鈥� Clark said in the statement. 鈥淭his is where more fossil specimens and more statistical models will come into play in the future 鈥� so stay tuned!鈥�
Understanding extinct species
Clark is currently researching new specimens that showcase both the surprising similarities and differences between ancient and modern birds, revealing what 鈥渓ittle paradoxical creatures鈥� they can be.
Clark credits his interest in the natural sciences to watching Attenborough鈥檚 nature documentaries, hence the name of the new fossil.
鈥淚t is a great honour to have one鈥檚 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,鈥� Attenborough said in a statement.
But studying extinct animals doesn鈥檛 just shed light on the past 鈥� it also raises awareness for the future, according to the researchers.
鈥淟earning 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鈥檙e in now,鈥� O鈥機onnor said. 鈥淭he 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.鈥�
