New look at ancient jaw fossil rewrites bird evolution | Science

Misidentified for decades, a tiny broken bone changed scientists’ view of bird evolution. For nearly 200 years, zoologists have divided birds into two groups: those with locomotion, where the jaw joints move their upper beaks, and a smaller group of birds, such as ostriches and emus, with fused upper palates. flexible upper beak. Because this fused palate is also present in dinosaurs, including the feathered birds that are the ancestors of today’s birds, zoologists believe that ostriches and their relatives are an evolutionary old group of birds with mobile upper beaks late in the history of birds.

Now, paleontologists have discovered the main bone of the skull of an ancient bird that lived 67 million years ago, just before the asteroid impact that killed the dinosaurs. The bone, which is part of the upper jaw, is very similar to the mobile body in today’s chickens and ducks, leading the researchers to conclude that ancient birds had upper beaks. They suspect that articulated beaks were also present in ancient birds, as the remaining specimens show that they were avian relatives. Ichthyornis, another ancient bird that lived 20 million years ago. Overall, the new analysis suggests that articulating beaks were already present in the ancestors of modern birds, and that ostriches and their relatives re-evolved laterally.

“Since the time of Linnaeus, the way we’ve looked at bird evolution has been changing,” said Christopher Torres, a paleontologist at Ohio University in Athens, who was not involved in the new job. “We thought it was solved centuries ago, and now we’re finding findings that show it wasn’t. We mixed it up.”

Janavis completes the bone
CT scans of this embedded fossil reveal the main jawbone of an ancient bird.Juan Benito, Daniel Field / University of Cambridge

The fossil, discovered more than 20 years ago in a Belgian quarry near the Dutch border, was first partially described in 2002, but many of its parts remained embedded in the sediment. University of Cambridge paleontologists Juan Benito and Daniel Field, who study bird evolution, borrowed the fossil from the Maastricht Museum of Natural History in 2018 and were able to image the remains using CT scans.

They hoped to find the animal’s skull, but initial tests revealed only vertebrae and ribs. Frustrated, they shelved the project for more than a year. When Benito returned to the fossil site, he was surprised to see the bone, which the analysis had previously identified as part of a shoulder, but it seemed too small. He realized that the piece was a bone fragment that had been split in two.

After identifying the companion piece and putting the two together, Benito, Field, and their colleagues concluded that the complete structure is a particularly delicate part of the upper palate, a bone called the pterygoid, which is the key to an articulated upper beak. Researchers, Who describes more complete fossils today? Natureargue that the bird is a previously unknown species and name it Janavis made it to the finals, as Janus, the Roman god of beginnings, endings, and transitions. It was a coastal aircraft that hovered over the shallow seas covering what is now Belgium and the Netherlands, and weighed about 1.5 kilograms, about the size of a gray heron.

Julia Clark, a paleontologist at the University of Texas at Austin, studies bird evolution. Janavis The fossil “is an important snapshot of the skull in a new way and adds to the evidence of what collection of features are ancestral to modern birds.”

Several old skulls Ichthyornis relatives Defined in recent years he has bones it was suggested that the upper palate of the bird might be attached, but the evidence remained murky. Now, inside Janavis “The bones of the skull were necessary to keep the upper beak flexible,” Field said. Torres agrees. “He’s like a piece of the puzzle that was missing, and now we have it,” he said.

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