First, paleontologists spread the word that modern birds are actually living dinosaurs. Then came the news from China that some dinosaurs and related reptiles long ago seemed to be marvelous four-winged creatures, seemingly on standby at some runway for takeoff in flight as early birds.
This handout photo shows a Sapeornis, a type of bird that until now was not believed to have hind feathers. But scientists in China say that some primitive birds used four wings more than 120 million years ago, before evolution led them to ditch their hind feathers in favor of scaly feet. (AFP / Getty Images)
Now, Chinese scientists have made a detailed analysis of 11 four-winged fossil specimens that lived about 130 million years ago. They reported Thursday in the journal Science that the study provided the first “solid evidence” that some recently excavated primitive bird species had also adopted the four-wing body plan before they ditched the hind-limb feathers and continued alone with the presumably more efficient feathered forelimb wings.
This evolutionary transition in early birds, the Chinese paleontologists said, “may have played an important role in the evolution of flight.”
At the time, these “basal bird” species appeared to be replacing their hind-limb feathers with scales and developing more birdlike feet. The researchers suggested that the four-winged creatures were already getting ready to use their hind limbs for terrestrial locomotion, like the robin pursuing worms on a lawn or the disputatious crow strutting around an overturned trash can.
The first Chinese discoveries of these feathered limbs were made at the turn of this century in dinosaur species named Microraptor and Sinornithosaurus. It is widely accepted that the large leg feathers in Microraptor were used in aerial locomotion, either in powered flight or merely gliding between trees or parachuting to the ground.
Although the new findings confirmed the presence of four-feathered wings early in the bird lineage as well, the Chinese scientists conceded that the aerodynamic function of this configuration remains debatable. Yet the research team, led by Zheng Xiaoting, of the Shandong Tianyu Museum of Nature, wrote that the stiff vanes and curving feathers in certain dinosaurs and the basal birds were “aerodynamic in function, providing lift, creating drag and/or enhancing maneuverability, and thus played a role in flight.”
The research team, which also included Xu Xing, a prominent dinosaur investigator at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, examined fossils found in Liaoning Province in northeastern China, a mother lode of remains from the early Cretaceous period. The work on the 11 basal bird specimens, which included several Sapeornis, Yanornis and Confuciusornis species, was conducted mainly at the Shandong Tianyu Museum of Nature.
Dr. Zheng’s group acknowledged that the way many of the specimens were preserved, revealed only in two dimensions, made it difficult to reconstruct the precise location and orientation of the leg feathers. Each skeleton, for example, is preserved either with the legs splayed outward or with the legs in a crouched position under the body. Nevertheless, the researchers wrote, “there is circumstantial data that might be useful in inferring the distribution and orientation of leg feathers.”
Generally, the leg feathers of modern birds, if they exist at all, are less developed than the arm feathers. They are usually small and fluffy, as in some chickens and pouter pigeons. They presumably serve to protect and insulate the legs, not to help in flight.
Mark A. Norell, a dinosaur paleontologist at the American Museum of Natural History in New York City, did not participate in the investigation but was shown the fossils on recent trips to China. “The work is most interesting,” he said, “but I would like to see a denser sampling” before reaching firm conclusions about the specific importance of the four-wing transition in the origin of bird flight.
He added, “We’ve known for a while, from Microraptor, about specimens with feathers down to their toes, and with feet already resembling those of modern birds.”
Dr. Norell and other paleontologists said the rich Cretaceous fossil beds of China had opened wide a window on the rise of feathered dinosaurs and the early evolution of birds. No one can tell yet how long the transition from four to two wings took.
The 150-million-year-old Archaeopteryx from Germany, sometimes called the first bird, probably had feathers on its forelimbs. But recent fossil finds question whether it was a birdlike dinosaur rather than a dinosaurlike member of the true bird lineage. So the Chinese team wrote that, only until now, no examples of the unusual four-wing structure “have so far been reported in basal birds.”