A small, lizard-like creature that lived 220 million years ago is at the centre of renewed debate over whether it had feathers and could fly.

Canadian scientists have concluded that the reptile had highly modified scales, rather than feathers, and therefore could not have been the distant ancestor of birds.

Earlier this year, a rival scientific team said fossil remains of the animal, Longisquama insignis, pointed to the presence of feathers.

They argued that it was unlikely that features as complex and specialised as feathers evolved more than once. This theory challenges the convention that the first bird, Archaeopteryx, arose 75 million years later, from small, meat-eating dinosaurs.

Now, palaeontologists at the University of Toronto have looked again at the fossils. They interpret what appear to be impressions of feathers preserved in rock as the marks left by long, thick scales.

They wrote in the scientific journal Nature: "We believe that the dorsal appendages of Longisquama are highly modified scales, as suggested previously, rather than feathers."

They say Archaeopteryx remains the oldest known forerunner of modern day birds.

Old specimen

The Longisquama specimen was discovered three decades ago in central Asia by a Russian palaeontologist who specialised in insects.

When the scientist published the first report of the fossil in 1970, he described a row of long narrow appendages down the animal's back, interpreting them as a frill of extremely long scales.

But in June, scientists at Oregon State University and colleagues came up with an alternative theory. After examining every detail of the fossils, which include most of the skeleton, they said they believed the unusual appendages showed some of the most recognisable features of a modern-day feather.

Longisquama probably glided, they said, rather than flew, using its long aerodynamic forelimbs for steering.

The new analysis is unlikely to be the final word in the debate. No-one has yet come up with a convincing explanation for what the scale-like structures did.

The Canadian team believe Longisquama could have used its scales to frighten predators or to attract a mate.

Other experts say the appendages could have been a "missing link" between scales and feathers.