Some 150 million years ago, Europe was tropical — and mostly underwater. The entire continent was closer to the equator than it is today, and what is now Germany and its neighbouring countries was submerged under a shallow inland sea, dotted with islands.
‘Weird’ dinosaur prompts rethink of bird evolution
On one cluster of islands, there were unusual creatures that didn’t fit in with the rest of the fauna. These were some of the earliest birds on the planet: about the size of crows, with black feathers, and probably partial to eating insects. They weren’t great fliers, spending most of their time on the ground and occasionally flapping into the air — perhaps to escape sneaking predators1. They also didn’t look like modern birds. They had teeth in their jaws and claws at the ends of their wings — features seen on no adult birds today. These German animals were Archaeopteryx, and they bore many traces of their dinosaur ancestors.
Fossils of Archaeopteryx are some of the most famous in history, but this creature is also an enigma. For more than a century, Archaeopteryx has been the only known bird genus from the Jurassic: the period when birds first evolved. Many other dinosaur-era birds have been discovered over the past few decades, but they are all from the subsequent period, the Cretaceous: a time when many diverse types of bird lived around the world. The group’s origins remained lost in time.
Now, researchers finally have a second genus of Jurassic birds. Baminornis, discovered in China and described in February 2025, instantly expanded scientists’ knowledge of the earliest birds. Baminornis is unlike Archaeopteryx, hinting at a complex evolutionary story. In parallel, the description of a remarkably well-preserved Archaeopteryx specimen, which had remained hidden for decades, has shed unprecedented light on the first birds. Finds such as these are revealing clues about how and why birds evolved, and whether they evolved powered flight just once or many times during the age of the dinosaurs.
From ground to air
Today, birds are one of the most successful and diverse animal groups, with about 10,000 known species2. They vary from minuscule hummingbirds that can hover in mid-air to great voyagers such as the wandering albatross, top predators such as golden eagles and large flightless creatures such as emus.
Over the past half century, researchers have established that birds evolved from dinosaurs: specifically, the theropods, the group that includes the turkey-sized Velociraptor and the towering Allosaurus.
However, reconstructing the evolutionary history of birds has proved remarkably tricky. “Birds and bird-like dinosaurs are super rare in the fossil record,” says Jingmai O’Connor, a palaeontologist at the Field Museum in Chicago, Illinois.
Blame anatomy for their rarity. “Birds, generally, are small and they have delicate, hollow bones and lightweight skeletons,” says Stephen Brusatte, a palaeontologist at the University of Edinburgh, UK. This means that their bones are more likely to be broken and crushed in rough environments, such as fast-flowing rivers, in which a large skeleton, such as that of a Tyrannosaurus rex, might survive.
The discovery of tertial feathers (inset) aids understanding of how Archaeopteryx flew.Credit: Delaney Drummond/Field Museum
Given all that, the preservation of Archaeopteryx fossils is something of a miracle. The first specimens were discovered in the early 1860s: initially a feather, which was the first fossil feather ever found3, and then a skeleton missing its head. The timing was fortunate: Charles Darwin had published On the Origin of Species in 1859, presenting his arguments that natural selection led to the formation of new species and, ultimately, radically new kinds of organism. The first Archaeopteryx fossil, discovered just a few years later, was a dramatic example of a transitional fossil: an animal with some bird-like traits but also some dinosaur-like traits.
Arguments have raged for decades about two key questions: could Archaeopteryx fly, and does it count as a bird? It did have pennaceous feathers, which help modern birds to fly4. But other aspects of its anatomy were less well-suited to sustained flight. “Archaeopteryx has a long tail, like a raptor dinosaur,” says Brusatte. This would have been awkward in flight: modern birds have short, stubby tail bones.
Likewise, Archaeopteryx doesn’t seem to have had a sternum (breastbone) to which the powerful wing muscles could have been attached. “That’s a really puzzling thing,” says Talia Lowi-Merri, an evolutionary biologist at Harvard University in Cambridge, Massachusetts, who has shown that sternums evolved stepwise in later birds5.
It might be that Archaeopteryx had a sternum made of cartilage, which would not have fossilized, but this would have been a weaker anchor for the muscles than would bone. “If flight were present, it would be less strong than modern bird flight,” says Lowi-Merri. As a result, many biologists suspect that Archaeopteryx were poor fliers, like modern chickens.
Missing links
Despite the growing body of information about Archaeopteryx, it can tell us only so much. All the fossils come from Germany, from what were once islands in a shallow sea. Some of the islands had lagoons filled with calm and often saline water, into which Archaeopteryx bodies could fall and be slowly buried and fossilized. “That’s a one-in-a-trillion circumstance,” says Brusatte.
Worse, it is one point on a very long timeline. Archaeopteryx fossils are all about 150 million years old: from towards the end of the Jurassic period, which lasted from 201.4 million to 143.1 million years ago. But after Archaeopteryx, there are no more bird fossils for millions of years.
67-million-year-old fossil upends bird evolutionary tree
For the subsequent Cretaceous period (143.1 million to 66 million years ago), the story is different. In eastern Spain, the fossil site Las Hoyas has yielded several birds and bird-like dinosaurs since the 1980s. More recently, sites in northeast China have emerged as a treasure trove of delicate fossils, including birds, that were part of the Jehol Biota, an ecosystem that existed about 135 million to 120 million years ago.
“There’s so many Cretaceous birds,” says Brusatte. Many are not the ancestors of living birds: instead, they belong to groups, such as the enantiornithines, that died out at the end of the Cretaceous, in the asteroid-related mass extinction that also wiped out all non-bird dinosaurs.
All told, Cretaceous birds and bird-like dinosaurs are known from Eastern Asia, North and South America, Madagascar and Antarctica. Clearly, by the early Cretaceous, birds had diversified and gone global.
But the late Jurassic cupboard remained frustratingly bare save Archaeopteryx — until the discovery of Baminornis.
Second Jurassic bird
Since 2022, palaeontologist Min Wang at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing and his colleagues have been exploring a new collection of fossils: the Zhenghe Fauna, in Fujian province in southeast China. Within the first year, they found a fossil they named Fujianvenator: a bird-like dinosaur probably more closely related to birds than to other dinosaurs. Fujianvenator had long hindlimbs, which suggested that it might have spent a lot of time wading in water. The team dated the Zhenghe Fauna to 148 million to 150 million years ago: roughly contemporary with Archaeopteryx6.
“This specimen gave us a lot of hope,” says Wang. “Maybe we could find some more interesting fossils in that locality.” The presence of freshwater animals such as turtles and small fish indicated that the Zhenghe Fauna was the preserved remains of a wetland: an ideal preservation spot for birds.
The researchers soon hit the jackpot, and described7 Baminornis in February 2025. It was a small bird, with a mass of 140–300 grams. Most strikingly, the five lowest vertebrae of the tail had fused together to form a stumpy bone called the pygostyle. This is the norm in modern birds and is also seen in Cretaceous birds, but is absent in Baminornis’s famous contemporary, Archaeopteryx.
This was a surprise, Wang says. Given how early Baminornis was, one might have expected to find a transitional stage — “maybe some birds have a shorter tail but still do not have a pygostyle” — but instead, his team found a Jurassic bird with a fully formed pygostyle. He argues that this means the first birds might have predated Archaeopteryx and Baminornis. “It pushed back the emergence of the origination of birds much earlier than we thought,” he says. “Is it possible that maybe some middle or early Jurassic birds had already evolved?”
Palaeontologist Min Wang points to the fused tail bones, or pygostyle, of Baminornis, a Jurassic bird discovered in China.Credit: Jin Liwang/Xinhua/Alamy
“It’s telling us that birds already had been experimenting and developing more-sophisticated aerodynamic and flying styles by the end of the Jurassic,” says Brusatte. The fact that Archaeopteryx and Baminornis were so different suggests that birds were already diversified, hinting at an earlier evolutionary history than previously thought.
However, O’Connor cautions against drawing big conclusions from Baminornis, because early interpretations of new fossils can prove to be incorrect on closer examination. “I think we still need to wait to really understand what the significance of these fossils is going to be,” she says.
In any case, even with Baminornis, the Jurassic bird record is still extremely thin, meaning that many questions remain unanswered. “Did birds go global as soon as they originated?” wonders Brusatte. Pterosaurs and bats, the other flying vertebrates, spread quickly — but if Jurassic birds did the same, scientists haven’t found the traces yet.
