Researchers have created the most comprehensive family tree of meat-eating dinosaurs to figure out how birds evolved from the extinct creatures.
They found that birdlike features such as feathers, wings and wishbones had developed gradually over tens of millions of years. But once a fully functioning bird body was complete, birds began to evolve much more rapidly, which eventually led to the emergence of the thousands of species that we know today, according to the results of the new study, published Thursday in the journal Current Biology.
And, since the emergence of birds some 150 million years ago was a slow process, during which dinosaurs became ever-more bird-like over time, it is hard for scientists to draw a clear dividing line on the family tree between dinosaurs and birds.
"There was no moment in time when a dinosaur became a bird, and there is no single missing link between them," study author Steve Brusatte, of the University of Edinburgh's School of GeoSciences in Scotland, said in a statement. "What we think of as the classic bird skeleton was pieced together gradually over tens of millions of years. Once it came together fully, it unlocked great evolutionary potential that allowed birds to evolve at a super-charged rate."
In the study, the investigators examined the evolutionary links between ancient birds and their closest dinosaur relatives by analyzing more than 850 body features in 150 extinct species. They used statistics to analyze their findings to assemble a complete family tree.
The new findings support a controversial theory proposed in the 1940s, which suggested that the emergence of new body shapes in groups of species could lead to a surge in their evolution.
"Our study adds to a growing number of works that approach this problem from different angles, but all seem to confirm that the origin of birds was a truly special event in Earth history," study author Graeme Lloyd, of the University of Oxford in England, said in a statement. "It is particularly cool that it is evidence from the fossil record that shows how an oddball offshoot of the dinosaurs paved the way for the spectacular variety of bird species we see today."