Dinosaurs of a feather flew on four wings not two

The earliest aircraft relied on two sets of wings to get airborne and so too did the earliest birds it seems. Palaeontologists in China have identified 150 million year old bird fossils that sported not one but two pairs of feathered wings.

Scientists agree that birds evolved from some species of dinosaur, a view that was bolstered by the discovery some years ago that they had feathers on their limbs, both front and hind.

What was missing was evidence of this four-winged body plan in early primitive birds rather than land-lubber dinosaurs. These have now been found after a trawl through fossils at China's Shandong Tianu Museum of Nature by Ziaoting Zheng and colleagues from the Chinese Academy of Sciences in Beijing.

They discovered no less than 11 primitive bird species with front wings but also feathered hind legs. And these were not just downy feathers used for display or staying warm, they were long, stiff-veined feathers of the kind used for flight, the authors write this morning (15th) in the journal Science .

The fossils were given to the museum by collectors who recovered them from the Jehol formation in northeastern China. The rock formations put them into the 100 to 150 million year old age bracket.

Xing Xu of the Institute of Vertebrate Palaeontology and Palaeoanthropology in Beijing, suspected that the earliest birds must have had this four-winged body shape and now there are fossils that back up this view.

All of these animals had flight-like feathers on front and hind limbs. And the feathers on the hind limbs had enough surface area to contribute to the aerodynamics of these early birds, the researchers suggest.

The question remains however whether the feathered hind limbs actually worked like wings or were nothing more than insulation or for use in sexual display. At the very least they could have been used for gliding and would have helped sustain gliding flight. The rear wings would also have created significant aerodynamic drag however.

What is not in doubt is the fact these primitive birds provide strong evidence that four-winged birds preceded two-winged birds, the authors argue. Over evolutionary time the feathers on hind limbs disappeared in favour of the scales seen on bird feet and legs today. It meant that a “decoupling” of limb function occurred where “the arms became specialised for flight and the legs for terrestrial locomotion”, the authors write. Ends