How Bird Beaks Got Their Start As Dinosaur Snouts
MAY 12, 2015 7:32 PM ET
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The skull of a chicken embryo (left) has a recognizable beak. But when scientists block the expression of two particular genes, the embryo develops a rounded "snout" (center) that looks something like an alligator's skull (right).Bhart-Anjan S. Bhullar
Scientists say they have reversed a bit of bird evolution in the lab and re-created a dinosaurlike snout in developing chickens.
"In this work, we can clearly see a comeback of the characteristics which we see in some of the first birds," says Arhat Abzhanov, an evolutionary biologist at Harvard University.
The ancestors of birds are a group of dinosaurs that includes the famous velociraptor, Abzhanov says. This group of meat-eaters had long snouts, small brains and eyes, and lots of teeth. Somehow they transformed into birds, which have none of those things.
Bhart-Anjan Bhullar, another member of the research team at Yale University, says the goal is to understand exactly how birds became birds. "What's the deep history of birdiness?" wonders Bhullar. "How did the different parts of their body plan form?"
An artist's rendition of anchiornis, a non-avian dinosaur(top), and a modern tinamou, with key bones highlighted in each face.John Conway一個藝術家的演繹，anchiornis，一個非鳥類恐龍（頂部），以及一個現代化的tinamou，與主要的骨頭中的每個face. John康威強調
In particular, he and his colleagues are interested in birds' distinctive beak, which Bhullar calls "this insane sort of snout that they have."
To hunt for clues about the origin of the beak, the researchers have been studying various kinds of animal embryos, from birds like emus and chickens to nonbird reptiles like alligators, which are birds' closest living relatives.
Their work led them to two specific genes. These genes are active in the middle of the face-forming region of bird embryos, but not in the middle of that region in the embryos of other animals.
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The team did an experiment to see what would happen if they blocked the effect of that localized gene activity in chicken embryos.
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Bhullar says he remembers the night he put the altered, developing chicks under a microscope, and saw that they had unusual, broad snouts.
"That was a pretty remarkable moment," he recalls. "That's a moment that will stay with me, I think."
Instead of the normal bone structure that would form a beak, he says, these protochickens had a pair of small, rounded bones that looked "like those in a dinosaur, like archaeopteryx or velociraptor, or in any other reptile — like an alligator."而不是正常的骨骼結構，將形成喙，他說，這些protochickens有一對小而圓的骨頭，看起來“像一個恐龍，始祖鳥一樣迅猛或，或以任何其他爬行動物 - 鱷魚般的”
A report on the study appears this week in the journal Evolution. But don't expect the scientists to create lab-grown dinosaurs — that would be a whole lot harder than just trying to restore some of the traits that existed in the first birds.