Birds have an enormously long evolutionary history - the earliest of them, the famed Archaeopteryx, lived 150 million years ago in what is now southern Germany.
However, whether these early birds were capable of flying and, if so, how well has remained shrouded in scientific controversy.
The 125-million-year-old fossil of the right wing of the primitive bird from central Spain preserves not only the articulated bones of the forelimb but also abundant remains of the plumage and of the soft-tissues of the wing.
This network ensures the position and controls the fine adjustments of the wing's main feathers, allowing living birds to fly efficiently and master the sky.
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The presence of these structures in the wing of such a primitive bird supports the notion that at least some of the most ancient birds were capable of performing aerodynamic feats in a fashion similar to those of many living birds.
"It's very surprising that despite being skeletally quite different from their modern counterparts, these primitive birds show striking similarities in their soft anatomy," said lead author Guillermo Navalon, PhD student at University of Bristol in UK.
Ancient birds may have flown over the heads of dinosaurs but some aspects of the precise flight modes of these early fliers still remain unclear, researchers said.
"Fossils such as this are an open window to deep time and allow scientists access to the most intricate aspects of the early evolution of the flight of birds," said co-author Jesus Marugan Lobon from Universidad Autonoma in Spain.