66-million-year-old ‘wonderchicken’ offers lesson in resilience

When Daniel Field first saw it, his shouts echoed down the hall.

“That moment was probably the most shocking moment of my life, certainly the most shocking moment of my scientific career,” he says.

The chunk of rock didn’t look like much. It was small and uninspiring, about the size of a deck of cards, says Dr. Field, a paleontologist at the University of Cambridge. But fragments of birdlike bone poked out of it, and it was from the last days of the dinosaurs, so it bore further scrutiny. 

Birds are the only dinosaurs to have survived the mass extinction at the end of the Cretaceous Period some 66 million years ago. But bird bones from that era are extremely rare, so paleontologists know little about how those creatures persevered. 

Before Dr. Field and one of his students CT scanned the rock to see what else might be buried in there, they didn’t expect to find much. But when the X-ray image appeared on the screen, Dr. Field recounts, there was “this incredible, complete bird skull staring straight out of the block at us.”

The fossil offers rare clues about why birds endured the asteroid impact that wiped out their fellow dinosaurs. This tale of survival could illuminate modern lessons for resilience in the face of global catastrophe. 

“The most resilient things in the history of the world have been the plants and animals and other organisms that have survived mass extinctions, particularly the one at the end of the Cretaceous,” says Stephen Brusatte, a paleontologist at the University of Edinburgh who was not involved with the study. “That asteroid hit and everything changed in an instant. So if you want to think about resilience, looking into the fossil record to see what survived is a great place to start.”

Part chicken, part duck, all dinosaur

Dr. Field says the new fossil, described in a paper published Wednesday in the journal Nature, looks like what you’d get if you took the front of a chicken skull and attached it to the back of a duck skull. 

Because of its chicken-like face, the researchers nicknamed this ancient bird species “wonderchicken.” They also gave it a scientific name: Asteriornis, after the Greek Titan goddess of falling stars, Asteria.

This specimen came from shallow marine limestone in Belgium, suggesting that Asteriornis was a shorebird. Its slender sandpiper-like legs corroborate that idea, says Dr. Field. 

Compared with its iconic dinosaur contemporaries, Triceratops and Tyrannosaurus rex, Asteriornis would’ve been a humble creature, says Dr. Field. The bird probably would’ve been quite small even among chickens and ducks alive today. “If you looked at the wonderchicken next to a T. rex 66.7 million years ago,” he says, “you might not have been able to guess which one of those things was actually built to last.”

Scientists don’t actually know whether the wonderchicken species itself or even its direct ancestors survived the mass extinction. But the fossil has features that we see on birds alive today, which Dr. Field says suggests tantalizing clues about its potential ability to survive. 

Paleontologists have some ideas about what might have made the surviving birds so resilient. Perhaps bird beaks enabled those theropod dinosaurs to dig through the dust coating everything to find seeds to munch. Or maybe those birds could eat all the dead stuff lying around. Dr. Field and colleagues have also suggested that it was the ground-nesting birds that survived, because forests were devastated.

Perhaps it wasn’t so much a single trait, but a mix of traits. The ability to eat a wide range of foods, minimal body size and caloric needs, and the freedom of flight likely all contributed to a kind of flexibility that enabled them to shift with the ecosystems around them.

“Probably all of those things work together to give them a good hand of cards for surviving the extinction,” says Dr. Brusatte.

A special early bird

While Asteriornis’ resemblance to living birds could suggest that shared features promote survival, there could be another explanation, says Julia Clarke, a paleontologist at the University of Texas at Austin who was not involved in the study.

Traits don’t always persist because they are beneficial, she explains. Sometimes they stick around simply because they aren’t harmful enough for natural selection to weed them out.

Furthermore, Dr. Clarke says, there still aren’t enough fossil birds from that era to be able to make generalizations with any confidence. Dr. Clarke’s own research has focused extensively on one of the only other modern-like bird species known from right before the asteroid hit: Vegavis, a duck-like bird unearthed in Antarctica. 

Still, she says, “this new fossil is of key importance” precisely because there are so few complete fossils from that time. And those features that Asteriornis and Vegavis share with living birds make these species worth studying to learn about the origins of modern birds.

The question about why birds – and crocodiles, and mammals, and turtles, for that matter – survived the end-Cretaceous mass extinction could bear on our world today, says Dr. Clarke. But to understand the relevance in today’s rapidly changing climate, researchers have to figure out whether each group that survived did so for distinct reasons, or whether there is one cohesive pattern. 

Dr. Brusatte points out that small-bodied mammals were also survivors of the mass extinction, so perhaps being small and adaptable was broadly advantageous.

“The world after the asteroid was very different than the world before the asteroid,” says Dr. Brusatte. “And when catastrophe hits, sometimes very quickly, the dominant things can die out. And I think that should be a lesson for us, really.”

What’s needed “is more fossils from this point in Earth history,” Dr. Field says. “This isn’t the end of the story.”