How a Dinosaur’s Twisted Wrist Gave Rise to Modern Birds

The bones of a 160-million-year-old dinosaur are helping scientists solve one of evolution’s biggest mysteries: how birds gained flight. Hidden within the wrist of a small, feathered dinosaur lies a clue that connects today’s birds with their ancient relatives. A team from Yale University recently published a study that explains how a special wrist bone may have made this transition possible.

The dinosaur, Archaeopteryx, lived during the Jurassic Period. It looked like a mix between a bird and a reptile, complete with wings, feathers, and sharp teeth. Although it could glide or fly short distances, its flight ability was still limited. What made it unique, according to scientists, was a small, twisted wrist bone called the “semilunate carpal.”

This bone allowed the wrist to bend and fold like a bird’s wing does today. In modern birds, this motion helps with flapping and folding wings neatly when they aren’t flying. It was once believed that this feature developed only in later bird species. But researchers from Yale discovered that the same type of bone existed much earlier than expected—far back in the family tree of theropod dinosaurs.

“This shows that the evolution of flight didn’t just happen overnight,” said paleontologist Daniel Field. “It was a slow process with lots of small changes over millions of years.”

Theropods were a group of two-legged dinosaurs that includes famous creatures like Tyrannosaurus rex and Velociraptor. Over time, some of these dinosaurs developed feathers, smaller bodies, and lightweight bones. But for flight to truly work, wings had to fold and flap effectively. That’s where the semilunate carpal comes in.

The Yale study examined fossils from over 200 different species, including both birds and dinosaurs. The team used CT scans to take 3D images of wrist bones, then ran digital simulations to study how the bones moved.

They found that this twisted wrist bone wasn’t unique to birds—it had already appeared in non-flying dinosaurs. That meant birds didn’t invent it; they inherited it.

“The semilunate carpal evolved long before true flight did,” said study co-author Bhart-Anjan Bhullar. “It was probably used for grasping or prey capture first. Later, it became useful for flight.”

That kind of repurposing is common in evolution. Scientists call it “exaptation”—when a trait originally evolved for one purpose ends up serving another. In this case, a wrist bone that once helped dinosaurs snatch food may have become a crucial part of the bird wing.

What really surprised researchers was how early this bone appeared. The Yale study shows that some dinosaurs had a semilunate carpal 40 million years before the first known bird took to the skies. This forces scientists to rethink the timeline of how flight evolved.

In birds, the wrist bends at a sharp angle to fold the wing. This folding is essential, both to protect feathers and to generate strong downward force while flying. Without it, birds would have a hard time taking off or landing.

The researchers believe the wrist’s flexibility helped some theropods climb, grasp branches, or handle prey. Over time, this same movement made the perfect foundation for powered flight.

The paper, published in the journal, Nature, points out that this wrist joint became more bird-like in stages. At first, it allowed some side-to-side movement. Later, it rotated more freely, and eventually it could bend sharply like a hinge. These steps match changes seen in the fossil record.

By comparing wrist structures across hundreds of fossils, the team created a timeline showing exactly when and how the wrist evolved. Their results showed strong links between wrist flexibility and the appearance of other flight-related traits like feathers and smaller body size.

Bhullar said, “You can trace this transformation bone by bone, trait by trait. It’s like watching evolution in slow motion.”

This discovery isn’t just about understanding the past. It also helps explain why birds are the only group of dinosaurs that survived the mass extinction 66 million years ago. Their unique skeletons—lightweight, flexible, and flight-ready—may have given them a better shot at survival.

It also shows how small changes in anatomy can lead to big changes in behavior and lifestyle. A twisted wrist may seem minor, but it was one of many steps that eventually led to powered flight, migration, nest-building, and all the behaviors we associate with birds today.

Even chickens and pigeons carry this ancient wrist structure. Every time a bird folds its wings, it’s repeating a motion that evolved millions of years ago in a world ruled by dinosaurs.

As Bhullar put it, “Modern birds are living dinosaurs. Their skeletons tell a story that’s still unfolding.”

This research also highlights the power of new technology in studying old bones. Using CT scans, digital modeling, and evolutionary trees, scientists can now uncover secrets hidden in fossils for decades. What once took years of guesswork can now be tested with precision.

And that’s just the beginning. The Yale team believes that similar studies could reveal even more about how animals have changed over time.

“Bones are like books,” said Field. “You just have to learn how to read them.”

Note: The article above provided above by The Brighter Side of News.

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