"Our understanding of the earliest evolution of Avialae has been hampered by the limited diversity of fossils from the Jurassic period," says Wang, who is also the lead and corresponding author of the new species study, which was conducted by the IVPP and the Fujian Institute of Geological Survey.

To date, no definitive avialan fossils have been unearthed except at the Middle-Late Jurassic Yanliao Biota in Northeast China (166 to 159 million years ago) and the slightly younger Solnhofen Limestone in Germany (about 155 million years ago), which preserves the remains of the Archaeopteryx, the fossil publicly known as the "first bird". This leaves a gap of about 30 million years before the oldest known evidence of Cretaceous birds.

The appearance of the Fujian fossil fills in part of that gap in early bird evolution, according to Bhart-Anjan Bhullar, a paleontologist at Yale University in the United States.

"Even at their earliest stages, the closest fossil relatives of birds were diversifying in interesting ways," Bhullar was quoted in an article in Nature.

"There are many, many such things left to be discovered. We've only scratched the surface of the anatomical and lifestyle diversity of these animals."

The Fujian avialan fossil exhibits a bizarre assembly of morphologies shared with other avialans, as well as with some non-avialan carnivorous theropods, Wang says, adding that this shows the impact of evolutionary mosaicism (the mixture of ancestral and derived features in a single specimen) in early bird evolution.

"Our comparative analyses show that marked changes to body plan occurred along the early avialan line, largely driven by the forelimb, which eventually gave rise to typical bird limb proportions," Wang says.

"However, Fujianvenator is an odd species that diverged from this main trajectory and evolved bizarre hind limb architecture."

The fossil's surprisingly elongated lower leg and other morphologies, in combination with other geological observations, suggest that Fujianvenator lived in a swamp-like environment and was a high-speed runner or a long legged wader, indicative of a previously unknown ecology for early avialans.

Wang has been extremely productive in the field of the origin and early evolution of birds, especially the way their features evolved across the bird-dinosaur transition during the Mesozoic era.