Newly discovered fossil, the ‘Wonderchicken,’ reveals the dawn of modern birds

Lead researcher Daniel Field holds a 3D printed version of the skull of the fossil bird Asteriornis maastrichtensis. Photo courtesy University of Cambridge

The oldest fossil of a modern bird yet found, dating from the age of dinosaurs, has been identified by an international team of paleontologists.

The spectacular fossil, affectionately nicknamed the “Wonderchicken,” includes a nearly complete skull hidden inside nondescript pieces of rock. It dates from less than one million years before the asteroid impact that eliminated all large dinosaurs.

The fossil, described today in the journal Nature, helps fill a gap in the fossil record because few specimens of crown birds exist from the Mesozoic era (around 250–66 million years ago). Crown birds are the common ancestors of all living birds, and all their descendants, whether living or extinct.

A shore-dwelling bird

Wonderchicken
An artist’s depiction of the world’s oldest modern bird, Asteriornis maastrichtensis, in its original environment. 66.7 million years ago parts of Belgium were covered by a shallow sea, and conditions were similar to modern tropical beaches like the Bahamas. Asteriornis lived at the end of the Age of Dinosaurs, a time when mosasaurs (giant marine reptiles) swam in the oceans, and Tyrannosaurus rex lived on land. Asteriornis had fairly long legs and may have prowled the tropical shoreline. Art by Phillip Krzeminski

Detailed analysis of the skull shows that it combines many features common to modern chicken- and duck-like birds, suggesting that the Wonderchicken is close to the last common ancestor of modern chickens and ducks. The fossil was found in a limestone quarry near the Belgian-Dutch border, making it the first modern bird from the age of dinosaurs found in the Northern Hemisphere.

The authors estimate that the bird weighed just under 400 grams (about 14 ounces). This relatively small size, together with its provenance from marine sediments, indicates that Wonderchicken may have been a shore-dwelling bird, which supports a hypothesis of shorebird-like origins for much of the diversity of crown birds.

The fossil doesn’t look like much at first glance. When it was found, only a few small leg bone fragments were poking out from a piece of rock the size of a deck of cards. Even those small bones attracted the researchers’ interest, since bird fossils from this point in Earth’s history are so rare.

Using high-resolution X-ray CT scans, the researchers peered through the rock to see what was lying beneath the surface. What they saw, just one millimeter beneath the rock, was the find of a lifetime: a nearly complete 66.7-million-year-old bird skull.

“The moment I first saw what was beneath the rock was the most exciting moment of my scientific career,” said Daniel Field from Cambridge’s Department of Earth Sciences, who led the research. “This is one of the best-preserved fossil bird skulls of any age, from anywhere in the world. We almost had to pinch ourselves when we saw it, knowing that it was from such an important time in Earth’s history.”

“Finding the skull blew my mind,” said co-author Juan Benito, also from Cambridge, who was CT scanning the fossils with Field when the skull was discovered. “Without these cutting-edge scans, we never would have known that we were holding the oldest modern bird skull in the world.”

Chicken-duck mash-up

The skull, despite its age, is clearly recognizable as a modern bird. It combines many features common to the group that includes living chickens and ducks – a group called Galloanserae. Field describes the skull as a kind of “mash-up” of a chicken and a duck.

“The origins of living bird diversity are shrouded in mystery — other than knowing that modern birds arose at some point toward the end of the age of dinosaurs, we have very little fossil evidence of them until after the asteroid hit,” said co-author Albert Chen, a PhD student based at Cambridge. “This fossil provides our earliest direct glimpse of what modern birds were like during the initial stages of their evolutionary history.”

A comparison of the skulls of a living galliform (a turkey), a living anseriform (a mallard), and the fossil Asteriornis maastrichtensis, in top view. Images not to scale. Image by Daniel J. Field, University of Cambridge

While the fossil is colloquially known as the Wonderchicken, the researchers have given it the slightly more elegant name of Asteriornis maastrichtensis, in reference to Asteria, the Greek Titan goddess of falling stars.

“We thought it was an appropriate name for a creature that lived just before the end-Cretaceous asteroid impact,” said co-author Dr Daniel Ksepka from the Bruce Museum in Greenwich, Connecticut. “In Greek mythology, Asteria transforms herself into a quail, and we believe Asteriornis was close to the common ancestor that today includes quails, as well as chickens and ducks.”

‘Gives us a search image’

The fact that Asteriornis was found in Europe is another thing that makes it so extraordinary. “The late Cretaceous fossil record of birds from Europe is extremely sparse,” said co-author Dr John Jagt from the Natuurhistorische Museum Maastricht in the Netherlands. “The discovery of Asteriornis provides some of the first evidence that Europe was a key area in the early evolutionary history of modern birds.”

“This fossil tells us that early on, at least some modern birds were fairly small-bodied, ground-dwelling birds that lived near the seashore,” said Field. “Asteriornis now gives us a search image for future fossil discoveries – hopefully, it ushers in a new era of fossil finds that help clarify how, when and where modern birds first evolved.”

The announcement of the Wonderchicken find was supposed to coincide with a new “Dawn of the Wonderchicken” exhibit at Cambridge’s Sedgwick Museum of Earth Sciences. But the COVID-19 pandemic has forced the museum to close until further notice.

Thanks to the University of Cambridge and the journal Nature for providing this news.

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