Before birds could fly on two wings, they had to ditch their training wings. This idea, first put forward a decade ago, is gaining credence with the discovery of 11 early bird fossils that seem to suggest that birds â€“ which evolved from feathered dinosaurs â€“ once had four wings.
In 2003, a group of Chinese researchers excavated six fossils of flying dinosaurs with wings on their hind legs. They called the creatures Microraptor.
“When we published that ten years ago there was some suspicion whether the fossil was faked,” says Xing Xu from Linyi University in Shandong province. Since then, more four-winged dinosaurs have been found, but doubt remained about whether they were ancestors of modern birds, or whether they simply died out rather than evolved, says Xu.
Now Xu and colleagues have described another find supporting their claim. In a collection at the Shandong Tianyu Museum of Nature, they came across nearly 2000 complete early bird fossils excavated 10 to 15 years ago. These included a series of bird skeletons that have large feathers on their hind legs, which Xu thinks were likely to have been for flight rather than display. All 11 specimens lived in the Early Cretaceous, about 120 million years ago, and seem to fall into several primitive bird groups.
The find means the branch on the tree of life that contains modern birds is now surrounded by animals that look as if they had four wings, leaving little room for four-winged dinosaurs to be an evolutionary dead end, says Steve Salisbury of the University of Queensland in Australia, who wasn’t involved in the work.