The past hundred million years or so have not been kind to the dinosaurs. Once formidable “terrible lizards,” their closest modern descendant is the distinctly unimpressive chicken.

Now scientists say they have turned back the clock on evolution — at least, in one small aspect of anatomy. By manipulating proteins in embryonic chicken cells, they were able to turn a bird’s beak into something more closely resembling the dinosaur’s snout from which it evolved.

This is an artist's conception of the dinosaur Anchiornis and a modern tinamou with premaxillary and palate bumps highlighted. Scientists have replicated the molecular processes that led from dinosaur snouts to the first bird beaks. Illustration by John Conway/Courtesy of Yale University

The Jurassic Park-esque experiment, reported in a study in the journal “Evolution,” didn’t quite hatch a dinosaur from a bird’s egg. But that was never the point, lead author Bhart-Anjan Bhullar, a paleontologist at Yale University, said in a news release.

Instead, by reversing the process that allows chickens to develop beaks rather than snouts, Bhullar and his colleagues gained insight into how the fearsome predators evolved into feathered poultry in the first place.

The beak came along fairly late in bird evolution, according to the New York Times. At that point, early birds had already developed feathers and the ability to fly. But their noses were still blunt and primitive, not the sophisticated, snapping beaks birds use today.

Those developed from a pair of bones called premaxillae, which sit near the front of most animals’ jaws. Previous research on the dinosaur-to-chicken evolutionary link showed that, over the course of millennia, these small bones fused and elongated, becoming a beak.

But in order to reverse that process, Bhullar had to understand how the beak formed in the first place, so he and his team looked at previous studies of chicken embryos. They found that chickens, emus and other birds release large patches of certain proteins during embyronic development, while mice and other beak-less animals produce smaller smatterings of the same proteins.

So the scientists released chemical inhibitors into what would become the faces of the embryonic chickens. These blocked the production of the proteins — and the beaks they would eventually create. Instead, the chickens grew a pair of rounded, unfused bones where normally their beaks would be.

But that wasn’t the only change the scientists saw. The birds’ palates reverted to their ancestral states as well, indicating that small molecular changes can have big consequences on anatomy.

A flap of skin covering their altered skulls obscured the ways the birds’ beaks had changed. But by creating digital models of the embryos’ skeletons, Bhullar and his team were able to examine the subtle ways the birds’ manipulated jaws more closely resembled those of ancient creatures like Archaeopteryx and Velociraptors than a modern-day chicken’s beak.

“Looking at these animals externally, you would still think it’s a beak. But if you saw the skeleton, you’d just be very confused,” Bhullar told Wired.

Some experts are skeptical of the finding, arguing that beak evolution was too slow and messy a process to be explained by one gene and a couple of proteins. Ralph Marcucio, a developmental biologist at the University of California, San Francisco, pointed out that the chemical inhibitor Bhullar and his team used to prevent beak development has toxic side effects — perhaps chickens’ skulls were altered simply because the tissue that would normally grow there had died, not because an evolutionary process had been reversed.

“It’s a simple kind of thing, but when you look at the actual pieces of data, it tends to fall apart,” he told the New York Times. “It takes away from the complexity that’s the reality.”

But Jack Horner, a paleontologist at Montana State University who has long argued that dinosaurs can be reverse-engineered from chickens, called the study “fantastic.”

“It’s an exciting time, and I envy people in the beginnings of their careers,” he told the Times.

It’s not unusual for modern animals to show traces of their ancestral anatomy, as Wired reported in 2011. For example, whales are occasionally born with leg-like appendages, an echo of the time when they once walked on land. Scientist believe these evolutionary throwbacks are possible because some adaptations aren’t caused by genes changing or disappearing — instead, they’re just turned off.

In his 2009 book “How to Build a Dinosaur” Horner proposed that those genes could be turned back on again. If biologists could identify and reactivate the genes that differentiate chickens from dinosaurs, they might be able to nudge the birds back toward their ancestral roots.

“What we’re trying to do is take our chicken, modify it, and make a chickenosaurus,” he said in a 2011 TED talk.

“It’s crazy,” he told Wired that same year. “But it’s also possible.”

The beak-to-snout study seems to bring that theory to bear. But just because it’s possible doesn’t mean it’s a good idea, some scientists say.

Matthew Harris, a Harvard University geneticist who has engineered chicken embryos that express ancient genes for teeth, told The Post last fall that the “chickenosaurus” effort is misguided.

Horner “is asking a question: ‘Can you remake something that was once lost?’ It is the wrong question to ask. What are you going to learn if you could do it? Technically, you are going to have a messed-up chicken. It’s not a dinosaur. It’s never going to be a dinosaur. It’s just going to be a really awful monstrosity,” he said. “What we should ask is: Knowing the history of birds, what are the interesting parts of their biology that can tell us something about the dinosaurs?”

In the news release about his findings, Bhullar echoed that sentiment.

“Our goal here was to understand the molecular underpinnings of an important evolutionary transition, not to create a ‘dino-chicken’ simply for the sake of it,” he said.

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