Twenty years ago, near the border between Belgium and the Netherlands, an amateur fossil hunter named Maarten van Dinther picked up a featureless block of rock the size of a pack of cards. Though he didn’t know it at the time, the little slab contained a tiny and perfect skull from the oldest direct relative of modern birds ever discovered, a fowl that walked the Earth with dinosaurs.
The animal, affectionately dubbed the ‘wonderchicken’ by the international team of scientists that analyzed the fossil, lived 66.7 million years ago, just 700,000 years before the asteroid impact that killed off all non-avian dinosaurs. Named Asteriornis in a paper published today in Nature, the species—known from fossils of its hind limbs in addition to its skull—has features similar to both ducks and chickens, suggesting it was related to the shared ancestor of both groups.
“This is an extraordinary and exciting find, which reveals new insights in a very poorly known chapter of avian evolution,” says Gerald Mayr, an ornithologist and expert on bird evolution at the Senckenberg Research Institute in Frankfurt, Germany, who was not part of the new study.
Asteriornis was a long-legged shorebird that could probably fly and likely combed the beaches of late Cretaceous Europe, which then had strings of islands in warm and shallow seas and a climate similar to the present-day Bahamas.
Contemporary of T. rex
“This is the first time we've seen the well-preserved skull of a modern bird from the age of dinosaurs,” says study lead author Daniel Field, a paleontologist at the University of Cambridge. “Asteriornis provides us with our clearest glimpse yet of what modern birds were like at the … point in time when T. rex and Triceratops were still alive.”
The 66.7-million-year-old fossil comes from the Northern Hemisphere, while all other remains of modern birds from the Cretaceous period have been from the Southern Hemisphere. Such fossils include the bones of a duck-like species named Vegavis, which were found in 66.5-million-year-old rocks of the Antarctic Peninsula and described in 2005.
While many birds lived alongside the dinosaurs, the majority were members of archaic groups, such as the toothed Enantiornithes, which went extinct along with most of the larger land animals. All modern birds emerged from a single group called the Neornithes, which appeared toward the end of the Cretaceous. (Read about the prehistoric birds that survived the extinction event.)
“The specimen is beautiful, the first really nice Neornithine from the Cretaceous,” says Jingmai O’Connor, an expert on fossil birds at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China, who was not part of the new study.
Until now, most fossils of birds from the Cretaceous that were related to living species have been “fragmentary and dubious,” she says, but the new discovery hints at the potential to find additional well-preserved modern bird relatives that lived prior to the impact and extinction event.
Anatomy of a ‘wonderchicken’
Asteriornis likely resembled the last common ancestor of Anseriformes, an order of birds including ducks and geese, and Galliformes, such as chickens and turkeys. “We knew already that these clades split during the Cretaceous, so we knew the ancestors to these groups were around,” O’Connor says. “But now paleontologists have finally found one.”
The skulls of living chickens and ducks “are very different in the present day, so the skull of Asteriornis provides the first glimpse we’ve ever had at what the skull of the most recent common ancestor of these groups probably looked like,” Field says.
Other living bird groups that are thought to have appeared during the Cretaceous period include the Paleognath birds, such as ostriches, emus, rheas, and cassowaries. Paleognaths, Anseriformes, and Galliformes are some of the deepest branches in the family tree of modern birds, and many other bird groups may not have appeared until after the asteroid impact.
A chance discovery
After finding the ‘wonderchicken’ fossils in 2000, van Dinther donated the specimens to the Natural History Museum of Maastricht in the Netherlands. The curator of that museum and co-author of the new study, John Jagt, sent the four small blocks of rock with limb bones poking out to Field in 2018.
From the outward appearance of the fossils, Field had low hopes of finding anything more exciting than broken limb bones. But birds from the late Cretaceous are rare, so he decided to run the fossils through a high-resolution CT scanner to visualize what was concealed within the rock.
He and one of his PhD students, Juan Benito, were staggered to discover “a beautifully preserved, nearly complete, 3D skull of a modern bird,” Field says. “It is the first modern bird skull from the entire Mesozoic era, and one of the best preserved fossil bird skulls of any age.”
The discovery was one of the most exciting moments of Field’s scientific career to date, he says. The study authors named the new species after Asteria, the Greek Titan goddess of falling stars, who transformed herself into a quail—an appropriate name for a bird that lived shortly before the impact that marked the end of the era of dinosaurs, Field says.
Piecing together avian history
A number of finds in recent years have shed light on the prehistoric origins of living bird groups and how these animals managed to survive one of the biggest extinction events in Earth’s history. Fossil birds from both New Zealand and Antarctica that lived shortly after the impact were described as species in the past few years, Mayr says.
Because many of the oldest fossils of modern birds are from the Southern Hemisphere, including the previous record-holder for oldest modern bird, Vegavis from Antarctica, some paleontologists suggested that modern birds originated on the southern supercontinent of Gondwana during the time of the dinosaurs. But this new discovery of an even older bird than Vegavis in the Northern Hemisphere throws a wrench into this theory.
“At this point I think the only thing we can say for sure is that the geographic origins of modern birds are truly mysterious,” Field says. “Only future fossil discoveries will be able to tell us where on Earth modern birds originated.”