Fossil feathers reveal their hues

The origins of the stripes seen in the feathers have long been debated

The complex coloured plumage of extinct birds which once soared over the heads of dinosaurs could soon be revealed.

Scientists have shown they are able to interpret the colour patterns seen in 100-million-year-old fossil feathers.

Writing in the journal Biology Letters, US researchers reveal how ancient feathers found in Brazil displayed "striking" bands of black and white.

Previously, fossil experts could only guess at the range of hues exhibited by ancient birds and some dinosaurs.

"It solves a conundrum," explained Professor Mike Benton of the University of Bristol, commenting on the work.

Behavioural clues

The team from Yale University analysed fossil feathers from Brazil and Denmark, along with the plumage of modern birds.

The fossil feathers had an obvious striped pattern but its origin had long been debated, according to Professor Benton.

"The banding looks so life-like that it can't be geological in origin - it has to be biological," he said.

The melanosomes could reveal a range of different colours

"But then how do you square that with the well-known fact that the majority of organic molecules decay in thousands of years?"

Microscopic analysis of the dark bands showed they displayed a distinctive granular texture, made from thousands of tiny, densely-packed flattened spheres.

Researchers had previously interpreted these as fossilised bacteria, preserved as the feathers decomposed.

But analysis of modern birds' feathers showed a similar structure.

"There are particular cells that cluster into the dark areas of modern birds called melanosomes," explained Professor Benton.

"Somehow [the melanosomes] are retained and replaced during the preservation process and hence you preserve a very life like representation of the colour banding [in the fossils]."

Lighter areas in the fossils did not show the same textures, leading the team to conclude that the feathers once displayed distinct black and white stripes.

But studies of other modern birds have shown that other colours are marked by distinct arrangements of melanosomes, raising the possibility of reconstructing more ornate plumage.

The Yale team believe it could identify brown, red, buff and even iridescent colours. The technique may be applied to other creatures to reveal the colour of fur or even eyes, the team believes.

The findings could shed light on the lives of some extinct creatures.

Genetic clues

"It allows you in certain cases to combine this knowledge with other information to paint quite a remarkable picture of behaviour," Professor Benton said.

For example, it could give researchers clues about courtship displays and mating behaviours.

"It might give you a very clear handle on an aspect of the ecology that people would have thought impossible to divine for an ancient fossil," said Professor Benton.

Scientists have previously used genetic techniques to reveal the colours of extinct species.

In 2006, researchers showed that some woolly mammoths would have sported dark brown coats, while others had pale ginger or blond hair.

The information was gleaned by analysis of genetic material extracted from a 43,000-year-old woolly mammoth bone from Siberia.

The same technique has been difficult to apply to creatures as old as the dinosaurs because of the lack of well-preserved genetic material.