Fossil Reveals 'Wonderchicken,' The Earliest Known Modern Bird

Artist’s reconstruction of the Wonderchicken, or Asteriornis maastrichtensis. (Illustration: Phillip Krzeminski)

A fantastic fossil found in Belgium is offering new insights into the ancient birds that gave rise to the ones still around today.

The researchers who analysed the fossil, a team led by paleontologist Daniel Field from the University of Cambridge in the United Kingdom, have dubbed it “Wonderchicken,” but their formal paper on the subject, published today in Nature, refers to this early bird as Asteriornis maastrichtensis.

“We report a new crown bird from the Late Cretaceous of Belgium,” the authors declare in the new study. “The fossil is between 66.8 and 66.7 million years old—making it the oldest unambiguous crown bird fossil yet discovered—and provides important insight into the extent of Mesozoic neornithine diversification before the end-Cretaceous mass-extinction event, 66.02 million years ago.”

Artist’s reconstruction of the Wonderchicken, or Asteriornis maastrichtensis. (Illustration: Phillip Krzeminski)

It’s a wonderfully concise description of the new finding, though it’s packed with a lot of jargon that I’m happy to break down. In a nutshell, this discovery shows that modern birds emerged at the very tail-end of the dinosaur age, known as the Mesozoic. Asteriornis was stomping on Late Cretaceous beaches just several hundred thousand years before an asteroid annihilated all non-avian dinosaurs.

By “crown bird,” the scientists are referring to the group of birds from which the common ancestor of all living birds is descended. Super early birds, like Archaeopteryx, Fukuipteryx, and Jeholornis, emerged between 145 million and 120 million years ago during the Jurassic, but these feathered avian dinosaurs scarcely resemble the birds who now hang out in our backyards. For example, these ancient “basal” birds, as they’re known, required a long time to mature, boasted long tails, and lacked a pygostyle—a plate located at the tip of the backbone, which modern birds use to prop their flight feathers.

Basal birds are so far removed from crown birds that scientists can’t be sure which, if any, of their descendant species, known as neornithines, gave rise to modern birds.

Scientists do know that crown birds emerged during the ensuing Cretaceous period, but these animals are poorly represented in the fossil record. And in fact, paleontologists have only one decent example of a Cretaceous crown bird, a creature known as Vegavis iaai, plus a jumble of incomplete fossils that could come from crown birds. As a consequence, scientists don’t have a great understanding of the oldest modern birds, including their ecological circumstances, habitat, and immediate descendants.

Hence the importance of the new fossil, which was found in the Maastricht Formation of Belgium. The Asteriornis fossil is now the most convincing example of a crown bird from the Mesozoic era, and it’s the first crown bird fossil from the dinosaur age to be found with a fully intact skull. So complete was the cranium that the researchers were able to study it in three dimensions, a feat made possible by an X-ray CT scanner.

Three-dimensional image of the skull of the world’s oldest modern bird, Asteriornis maastrichtensis. (Image: Daniel J. Field, University of Cambridge)

The name Asteriornis comes from Asteria—the Greek god of falling stars who transformed into a quail. The new moniker is apt, with the falling stars representing the asteroid that triggered the end-Cretaceous mass extinction, and the quail representing fowl birds, to which Asteriornis bears a significant resemblance.

Indeed, physical analysis of the Asteriornis fossil revealed a mixed set of features consistent with both modern landfowls (also known as gamefowls) and waterfowls—two distinct but closely related evolutionary orders. Together, landfowls and gamefowls fit snugly inside a clade called Galloanserae, a group that includes ducks, chickens, turkey, geese, pheasants, and partridges. Fascinatingly, Asteriornis had cranial features common to chickens and ducks, which suggests its evolutionary position is near to the last common ancestor of chickens and ducks, according to the research.

Asteriornis was relatively small, weighing a smidge under 400 grams (0.88 pounds). In an email to Gizmodo, Field said this bird would be roughly equal in size to some of the world’s smallest ducks and almost identical in size to the green-winged teal, a common duck found in North America. Asteriornis had a bill similar to those found in chicken-like birds, but without a sharp hooked tip. The shape of its bill probably means Asteriornis had a diverse diet, explained Field.

“However, unlike living duck-like birds and chicken-like birds, the fossil seems to have been quite ‘leggy,’ with fairly long and slender hindlimbs,” Field told Gizmodo. “This is interesting because the fossil was found in rocks that were laid down in a shallow marine environment. Therefore, we think Asteriornis may have prowled the ancient shorelines of Europe, which at the time would have had beaches similar to what we see in the Bahamas—the world was much warmer at the time!”

Now, while Asteriornis may be the oldest known crown bird, it cannot be said that all birds living today are descended from it. In addition to Galloanserae, other living clades include Palaeognathae (a group that includes ostriches and related species) and Neoaves (basically all the other living birds, from parrots and robins through to woodpeckers and penguins).

Asteriornis seems to be close to the most recent common ancestor of Galloanserae, so it seems like all 300 living species of chicken-like birds and 177-living species of duck-like birds may be descended from an Asteriornis-like bird,” said Field. “Palaeognathae like ostriches and kiwis, and Neoaves like penguins are not descended from Asteriornis. But, things like ducks, geese, swans, turkeys, chickens, pheasants, quail, and so on, may have descended from an Asteriornis-like bird.”

As for Vegavis iaai, this alleged crown bird has now been knocked off its perch in terms of it being the oldest modern bird in the fossil record.

The generally agreed upon age for Vegavis is 66.5 million years old, according to work done by paleontologists Daniel Ksepka and Julia Clarke. At an estimated 66.7 million years old, Asteriornis is a bit older. What’s more, Vegavis might not actually be a crown bird, as some phylogenetic analyses (the placement of a species within its evolutionary family tree) have actually positioned it outside crown birds, explained Field.

“Personally I do think Vegavis is a crown bird, but the evidence is not as clear as the evidence from Asteriornis,” Field told Gizmodo. “Having a skull from Vegavis would clarify the situation a lot.”

As always, the search continues for more fossils, as scientists try to piece together the details of this fascinating and important stage in the evolution of birds.

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