The team found that two proteins known to orchestrate the development of the face, FGF and Wnt, were expressed differently in bird and reptile embryos. In reptiles, the proteins were active in two small areas in the part of the embryo that turns into the face. In birds, by contrast, both proteins were expressed in a large band across the same region in the embryo. Bhullar sees the result as tentative evidence that altered FGF and Wnt activity contributed to the evolution of the beak.
To test this idea, the team added biochemicals to block the activity of both proteins in dozens of developing chicken eggs. The researchers did not actually hatch the eggs, says Bhullar, because they did not write that step into their approved research protocol. Instead, they discerned differences in the faces of ready-to-hatch chicks, which looked subtly different from chicks without their proteins inhibited. The altered chicks still had a flap of skin over their would-be beaks, so the difference is not obvious, says Bhullar. “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," he says. "I would not say we gave birds snouts.”
In some embryos, the premaxillae were partly fused, whereas in others the two bones were distinct and much shorter; some of the altered embryos did not look all that different from those of regular chickens. The team created digital models of their skulls with a computed tomography scanner and found that some of these more closely resembled the bones of early birds such as Archaeopteryxand dinosaurs such as Velociraptor, than unmodified chickens.
“Very cool,” says Clifford Tabin, a developmental biologist at Harvard Medical School in Boston, Massachusetts. He thinks that Bhullar’s team makes a strong case that altered expression of FGF and Wnt shaped the bird's beak. Identifying the genetic changes responsible, however, will prove much more difficult. They could lie in the genes coding for FGF and Wnt, or to genes in related biochemical pathways, or in ‘regulatory’ DNA that influences gene expression. If these changes could be identified, it might be possible to modify chicken genomes to include them (and, conversely, to make reptiles more bird-like through genome editing).
Jack Horner, a palaeontologist at Montana State University in Bozeman, hopes to take a genetic approach to imbuing chickens with dinosaur-like tails. In a paper published last year2, his team identified mutations potentially involved in the disappearance of the tail in modern birds. But applying these insights to engineering ‘dino-chickens’ has proved difficult, he says. “We’re having a little more trouble with the tail. There are so many components.” Other anatomical features could be altered by tinkering with development proteins, Horner adds. “It gives us a lot of opportunities to think about making new kinds of animals.”
Bhullar says that he admires Horner’s vision, but he is more interested in replaying evolution to reveal how it creates new forms. His lab plans to study the expansion of the mammalian skull and the unusual lower limbs of crocodiles by resurrecting ancient anatomy. “I think it will open as big a window as you could possibly get into the deep past without having a time machine,” he says.