Cretaceous Enantiornithine Bird Was First of Its Kind with Toothless Beak

Paleontologists have described a new species of enantiornithine bird with a toothless beak from the Jehol avifauna of China. The discovery pushes back the earliest appearance of edentulism (toothlessness) in enantiornithines by approximately 48 million years.

Imparavis attenboroughi lived in what is now northeastern China some 120 million years ago (Early Cretaceous epoch).

This bird was a member of a group called Enantiornithes, or ‘opposite birds,’ named for a feature in their shoulder joints that is ‘opposite’ from what’s seen in modern birds.

Enantiornithines were once the most diverse group of birds, but they went extinct 66 million years ago following the meteor impact that killed most of the dinosaurs.

Paleontologists are still working to figure out why the enantiornithines went extinct and the ornithuromorphs, the group that gave rise to modern birds, survived.

“Enantiornithines are very weird. Most of them had teeth and still had clawed digits,” said Alex Clark, a Ph.D. student at the University of Chicago and the Field Museum.

“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.”

“Scientists previously thought that the first record of toothlessness in this group was about 72 million years ago, in the Late Cretaceous.”

“This little guy, Imparavis attenboroughi, pushes that back by about 48 to 50 million years. So toothlessness, or edentulism, evolved much earlier in this group than we thought.”

The fossilized skeleton of Imparavis attenboroughi was found by an amateur fossil collector near the village of Toudaoyingzi in northeastern China and donated to the Shandong Tianyu Museum of Nature.

“I think what drew me to the specimen wasn’t its lack of teeth — it was its forelimbs,” said Dr. Jingmai O’Connor, associate curator of fossil reptiles at the Field Museum.

“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.”

The unusual wing bones of Imparavis attenboroughi could have allowed for muscle attachments that let this bird flap its wings with extra power.

“We’re potentially looking at really strong wing beats,” Clark said.

“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.”

Meanwhile, the toothless beak of Imparavis attenboroughi doesn’t necessarily tell the researchers what it was eating, since modern toothless birds have a wide variety of diets.

Like its fellow enantiornithines, and unlike modern birds, it does not appear to have a digestive organ called a gizzard, or gastric mill, that helped it crush up its food.

“It seems like most enantiornithines were pretty arboreal, but the differences in the forelimb structure of Imparavis attenboroughi suggests that even though it’s 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,” Dr. O’Connor said.

Ii their study, the scientists also reexamined a previously known fossil bird, Chiappeavis, and suggest that it too was an early toothless enantiornithine.

“This finding, along with Imparavis attenboroughi, indicates that toothlessness may not have been quite as unique in Early Cretaceous enantiornithines as previously thought,” they said.

The specific name of Imparavis attenboroughi, in honor of naturalist Sir David Attenborough, means Attenborough’s strange bird.

“It is a great honor to have one’s name attached to a fossil, particularly one as spectacular and important as this,” Sir David Attenborough said.

“It seems the history of birds is more complex than we knew.”

“All birds are dinosaurs, but not all dinosaurs fall into the specialized type of dinosaurs known as birds, sort of like how all squares are rectangles, but not all rectangles are squares.”

“The newly described Imparavis attenboroughi is a bird, and therefore, also a dinosaur.”

A paper describing Imparavis attenboroughi was published online in the journal Cretaceous Research.

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Xiaoli Wang et al. 2024. First Edentulous Enantiornithine (Aves: Ornithothoraces) from the Lower Cretaceous Jehol Avifauna. Cretaceous Research 159: 105867; doi: 10.1016/j.cretres.2024.105867