WASHINGTON, March 14 (Xinhua) -- In order to achieve bipedal
flight, birds first had to ditch two hind wings over the course
of their evolution, according to a study to be published Friday
in the journal Science. Recently, several fossils have shown
that some dinosaurs had large feathers on both fore limbs and
hind limbs. But, until now, no examples of this four-winged body
plan have been described in birds -- or even in their most
recently extinct relatives. Xiaoting Zheng, of Linyi University
in China, and colleagues studied fossils in China's Shandong
Tianyu Museum of Nature and identified 11 primitive bird species
with clear signs of feathered hind legs. These findings suggest
that this four-winged condition preceded the two-winged body
plan, and that birds have gradually lost the feathers on their
hind limbs over evolutionary time. Such a transition from four
wings to two probably happened while the birds were gaining more
scales on their hind limbs and using them more for terrestrial
locomotion, accordi