When did the first representatives of modern birds emerge? So far there is no clear answer to this question. But now paleontologists in Belgium have discovered a fossil that could bring more clarity. It is the skull and some bones of a bird that lived 66.7 million years ago – shortly before the end of the Cretaceous Period. Its characteristics characterize the bird christened Asteriornis maastrichtensis as a close relative of the chicken and goose birds. This is the oldest fossil of a modern bird, as the researchers report. It is also one of only a few bird fossils found in Europe.
The first bird-like creatures developed around 150 million years ago in the Middle Jura, as evidenced by the famous Archeopteryx. These primeval birds were already feathered, had front legs shaped into wings and could fly – although probably not yet very elegantly. At the same time, however, they still had some features that showed their lineage from two-legged predatory dinosaurs, including their tooth-reinforced jaws. However, it is unclear when these primeval birds became the first representatives of modern, real birds: “The roots of modern bird diversity are puzzling – apart from the knowledge that modern birds appeared at some point towards the end of the dinosaur era, we only have a lot few fossil finds of them, ”explains co-author Albert Chen from the University of Cambridge. Most of these fossils date from the period immediately after the end of the Cretaceous period around 66 million years ago. The only clearly modern bird from before this break was Vegavis iaai, a representative of the goose-like species discovered in Antarctica and around 66.2 million years old.
A skull in the limestone block
But now Daniel Field from the University of Cambridge and his colleagues have found a bird fossil that is even older than Vegavis – and still comes from a modern bird. They discovered the relics in a limestone quarry near the Belgian city of Liège. Initially, only a few parts of a small leg bone protruded from a roughly 66.7 million year old rock. In order to clarify what was still hidden therein, the researchers brought him to the laboratory and examined him using high-resolution computed tomography. “The moment I saw what was hidden in the stone was the most exciting moment in my entire scientific career,” says Field. The almost completely preserved skull of a small bird was enclosed in the inconspicuous chunk of lime, along with some fragments of its skeleton.
“This is one of the best preserved fossil bird skulls ever found anywhere in the world,” says Field. It provides unique insights into the development and skull evolution of early modern birds. “We almost had to pinch ourselves when we saw him, because he also comes from such an important time in earth’s history.” With an age of around 66.7 million years, this bird lived just before the asteroid impact in the Cretaceous Age and ended the era of the dinosaurs. He is also around 500,000 years older than Vegavis iaai. The paleontologists have named their new find Asteriornis maastrichtensis – after the Greek titan Asteria. “We found this a suitable name for a creature that lived immediately before the asteroid impact,” says co-author Daniel Ksepka from the Bruce Museum in Connecticut. “In Greek mythology, Asteria also turns into a quail.”
Ancestor of the chickens and geese
Closer analyzes of the skull revealed that Asteriornis maastrichtensis was similar in many respects to today’s hen birds (Galliformes) and goose-like species (Anseriformes). The paleontologists therefore classify this bird as one of the last common ancestors of these groups of birds. The fossil thus helps to classify the origins of modern birds and the branching out of the different groups of modern birds. “The phylogenetic position of Asteriornis fits a limited diversification of modern birds already in the Cretaceous period and the survival of only some of these groups beyond the mass extinction at the end of the Cretaceous period,” explained Field and his team. “This fossil gives us the earliest insight into what modern birds looked like in the early stages of their evolutionary history.”
The dimensions of the skull and leg bones show that in terms of size and weight, Asteriornis was between the modern avocet and the oystercatcher – it weighed almost 400 grams. Like these waders, he might have been looking for food on the coast or on the banks of water. “This fossil tells us that at least some of the early modern bird representatives were rather small birds that lived near the coast,” says Field. The discovery of this fossil not only opens a window into the past of birds – it also proves that the area of today’s Europe could have played an important role in its development. “Finding bird fossils from the late Cretaceous period is extremely rare in Europe,” explains co-author John Jagt from the Natural History Museum Maastricht. “The discovery of Asteriornis now gives us one of the first proofs that Europe was a key region for the early evolution of modern birds.”
Source: Daniel Field (University of Cambridge, UK) et al., Nature, doi: 10.1038 / s41586-020-2096-0