Four-Winged Dinosaur Norellraptor Shows Flight Evolved Twice
Birds are not the only dinosaurs that grew feathers and wings. A small predator from China, with four wings, is now evidence that flight may have arisen more than once.
The exceptionally well-preserved dinosaur, named Norellraptor barsboldi, was 3 years old when it died and measured just 21 inches (57 centimeters) long. It comes from the Early Cretaceous Jiufotang Formation in northeastern China, which dates to between 145 million and 100 million years ago. It had sharply curved teeth and claws, the tools of a small generalist predator. Scott Hartman, a vertebrate paleontologist at the University of Wisconsin-Madison who was not involved in the study, said it probably ate early mammals, lizards, amphibians and juvenile dinosaurs, and would not have attacked large dinosaurs.
Close to birds, but not their ancestor
N. barsboldi was a microraptor. Microraptors were close relatives of birds, but not their ancestors. Birds belong to a neighboring group called Avialae. Both groups had feathers, and the puzzle has been whether flight began in an ancestor of both or whether feathers, and possibly flight, evolved more than once.
What the analysis found
Andrea Cau of the OPHIS Paleontological Museum in Italy and his colleagues found that around 30 percent of the 194 anatomical changes across microraptor evolution also evolved in the bird lineage. Those changes included feathers, fused bony projections on the ribs that made a rigid torso, robust forelimb bones and an ulna longer than the humerus. But the shared features evolved in a different order in the two groups. The team published the work on September 29 in Nature Communications.
Rui Pei of the Chinese Academy of Sciences, who was not part of the work, said microraptors acquired traits that converged with early stages of true birds through a distinct evolutionary pathway. He said this supports the idea that flapping flight evolved independently in non-avialan dinosaurs and birds.
How it may have moved
Hartman suggested microraptors mixed gliding and flapping. He doubted they could climb trees like squirrels, because their forelimbs lacked the range of motion. They may have taken off after running down a slope, or leapt from hills and cliffs. A large, well-ossified breastbone would have supported big flight muscles for a solid downstroke, and the hind wings likely stabilized flight and allowed tight turns. The wings may also have served other purposes, such as displaying to mates or warming eggs.
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