The world’s first bird has long been thought of as the Archaeopteryx, a feathered Jurassic-period animal that had the teeth and tail of a dinosaur. Several fossils have been found that support this theory, and even fossilized black feathers were found in Germany over a century ago. The feather suggests to scientists that winged animals during that period had almost identical flight technology as today’s birds, so it was rather an exciting find.

“It means that completely modern flight feathers had evolved as early as 150 million years ago, in the Jurassic period,” said study leader Ryan Carney, an evolutionary biologist at Brown University in Providence, Rhode Island.

But a new discovery is being hotly contested as the world’s “first bird”: Aurornis xui, which was found in a 160 million-year old rock formation in China. Though Aurornis xui is 10 million years older than Archaeopteryx, the two are extremely close in relation as the earliest bird life.

The problem some researchers have is that there’s no proof that these winged animals ever took flight; in fact, some think they were merely plumed versions of the dinosaurs we’re familiar with that never made it into the sky. The non-flying birds have been given the name deinonychosaurs.

“The problem we are facing these days is that all these animals are anatomically very similar, and our definition of birds—arbitrary as it is—sets a line between what is and what isn’t called a bird,” paleontologist Luis Chiappe says. “What the trees —and the new fossils—are telling us is that back in the Jurassic, 150 to 160 million years ago, many different types of dinosaurs were experimenting with ‘birdness’. And it is from this ‘birdness soup’ that true birds originated.”

Despite a lack of agreement between researchers, it seems the big picture is that birds did, indeed, evolve from dinosaurs, and that is what matters most to those who study the creatures.

Image: Masato Hattori