Fossils of small feathered dinosaurs like Archaeopteryx and Microraptor link our modern birds with the dinosaurs and have helped scientists map the evolution of birds and of flight. However, that evolution might have been more turbulent than previously thought. Archaeopteryx and Microraptor both show fossil evidence of feathers on their hindlimbs as well as their forelimbs. Microraptor’s leg feathers were long and stiff and even sprouted from their feet, earning their legs the title of wings just like their arms. Since Microraptor was discovered in 2000, scientists have disagreed on exactly how the dinosaur used this second set of what could have been wings.
Until recently, hind wings were thought to be a rare feature of dinosaurs. There were few examples of feathered hindlimbs; but they appeared on dinosaurs that were closely related to birds, but not their actual ancestors. A study published this month in Science magazine seems to prove the opposite.
Zheng Xiaoting from the Shandong Tianyu Museum of Nature, Xu Xing, from the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, and their associates took advantage of the plentiful fossil record found in China’s Jiufotang and Yixian formations to help solve this hind feather mystery. They researched 11 specimens of primitive birds from the early Cretaceous whose fossils showed evidence of four wings. Leg-wings in such a variety of species mean that they were no accident of biology and they weren’t the exclusive trait of bird-like dinosaurs. In fact, during the evolution of flight an intermediate four-winged stage may have occurred in some species before evolving to the two wings birds have now.
Some present day species of birds, such as chickens and pigeons, still have feathers on their legs for warmth and protection, though none grow feathers from their feet. Early leg feathers may have transformed into the scales found on bird legs today, which protect the legs but still allow birds to move easily across the ground, something their four winged ancestors almost certainly could not do.
Some scientists doubt whether the leg wings were much use for flying. Like most fossils, the birds Xiaoting and Xing examined were rather squashed, so it is difficult to tell exactly how these limbs moved or exactly where their feathers were attached. Some scientists claim that such long stiff feathers on the legs could only have produced drag during flight.
However, Xiaoting and Xing believe that the feathers were used in flight or else contributed to the birds’ ability to glide, probably from tree to tree in search of their next meal.
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You can find this study in Science magazine.
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