One of the latest breakthroughs from Yale scientists: the mighty dino-chicken. The Yale team used molecular manipulation to grow chicken embryos with Velociraptor snouts and published their results yesterday in the journal Evolution. The embryos did not hatch.
"The experimental animals did not have a beak, instead developing a broad, rounded snout," said Bhart-Anjan Bhullar, a paleontologist and developmental biologist at Yale University and the lead author of the study. "They still lacked teeth, and possessed a horny covering on the snout."
Although the embryos did not hatch, the team stresses: "They could have. They actually probably wouldn't have done that badly if they did hatch. Mostly, though, we were interested in the evolution of the beak, and not in hatching a 'dino-chicken' just for the sake of it."
The team hoped to gain an understanding of how the more rounded snouts of the dinosaurs might have evolved into modern bird beaks. To do this Bhullar and her team examined and compared the bones of modern birds with the fossils of beaked dinosaurs. Their strategy was to analyze genetic activity in the embryos of various animals. They investigated alligators, emus, turtles, and lizards, sampling DNA from specimens in various places.
They then discovered a pattern of gene expression unique to birds which controls the beak's shape. The scientists centered their efforts on two genes which influence the development of the center of the face. Next they created molecules to suppress the activity of these genes and the proteins they create, which stopped the creation of the beak. In this way the researchers caused the chicken embryos to grow a palate and snout like those of their prehistoric ancestors.
The team clarified that it is not yet possible to genetically modify chickens to resemble dinosaurs. "We're not altering the genes themselves yet - we're altering the proteins that the genes produce," Bhullar says.
Birds evolved from dinosaurs around 150 million years ago as their bodies learned to created feathers and beaks. The dinosaurs died out about 65 million years ago, probably due to a meteor 6 miles in diameter crashing into the Earth. At least, most of them died out; their modern relatives, birds, exist on all seven continents. This presents a rich opportunity for scientists.
"There are between 10,000 and 20,000 species of birds alive today, at least twice as many as the total number of mammal species, and so in many ways it is still the Age of Dinosaurs," Bhullar says.
The evolution of flight and the roles of feathers alongside the structure and development of beaks offer a wealth of information about the entire evolutionary process. Scientists believe that beaks provided the ability to grip and grasp in creatures that had arms that were mostly useless. Eventually then the arms evolved into wings. Since then, beaks have continued to change, and they are used in many ways: compare hummingbirds and pelicans for a good example of this diversity.
"The beak is a crucial part of the avian feeding apparatus, and is the component of the avian skeleton that has perhaps diversified most extensively and most radically - consider flamingos, parrots, hawks, pelicans and hummingbirds, among others," Bhullar says. "Yet little work has been done on what exactly a beak is, anatomically, and how it got that way either evolutionarily or developmentally."
John R. Horner, a paleontologist at Montana State University, predicted that this kind of manipulation might be possible in his 2009 book: "How to Build a Dinosaur: The New Science of Reverse Evolution" (co-authored with James Gorman, a science reporter at The New York Times). "I think it's fantastic," Horner said of the study. "It's an exciting time, and I envy people in the beginnings of their careers."
Not everyone is convinced about the findings. Developmental biologist Ralph S. Marcucio of the University of California, San Francisco, was not persuaded by the new study although he did agree that the results are promising. Dr. Marcucio noted that the techniques used in the process may have side effects and that the transformed embryos may have been created by killing off cells accidentally. Marcucio believes that the process of beak evolution was more complex and likely involved other genes, not just those studied.
"It's a simple kind of thing, but when you look at the actual pieces of data, it tends to fall apart," Marcucio says. "It takes away from the complexity that's the reality."
More work in this area, perhaps done by the Yale team, may settle this dispute.
"I'm enormously eager to find the regulatory changes themselves," Bhullar says. "These techniques were in their infancy when I started the project, which shows you how fast the field is changing."
The team intends to study all of the genes involved in beak development moving forward. The team hopes that this discovery will lead to improved insights into a variety of evolutionary metamorphoses including the evolution of mammals from reptiles.
"I think it will open as big a window as you could possibly get into the deep past without having a time machine."
