Australian-Geographic-Magazine-September-Octobe..

September–October 2014 73

and round the tail – and so they would have had only a limited

function in thermoregulation [maintaining body temperature].”

His team, therefore, suggested that feathers arose initially for

colourful display purposes and later were co-opted for insulation

and eventually fl ight. The idea that display and communication

were the initial functions of feathers is interesting because most

experts believed the fi rst feathers were for insulation. If colour-

ful feathers evolved for display, they might have played a much

more integral role in the success, evolution and diversifi cation

of dinosaurs than has been supposed.

H

OW ON EARTH can you fi nd out anything about the

colour of feathers from the fossil record? I admit to

having been baffl ed by this when stories of the orange

plumage of Sinosauropteryx fi rst broke in 2010. To answer that

question, we have to look into a little of the science of how

animals make colour in the fi rst place.

The pigment that gives our hair and skin colour is called

melanin (from the Greek melanos, meaning dark) – it’s the same

substance that is produced when we sunbathe, causing fair-

skinned people to become tanned.

Like all pigments, melanin works by absorbing some wave-

lengths of light and refl ecting others to produce specifi c colours.

Inside hair and feathers, it’s wrapped in tiny packages known

as melanosomes, which create shades of black, grey, orange and

brown. When I say tiny, I mean really tiny; most are 200–600

nanometres (millionths of a millimetre) across. Two hundred

of them can fi t across a human hair.

Though diminutive, they are incredibly tough and actually

form part of the strong protein structure of hair and feathers.

They are so durable, in fact, that they can survive in fossils for

hundreds of millions of years.

According to Mike, until very recently people just wouldn’t

have believed melanin could be preserved. And it seemed even

less likely after a series of failed, highly publicised eff orts to recover

DNA from dinosaur bones in the 1990s made people extremely

cautious about attempting to retrieve proteins or any other

organic molecules from fossils. But it turns out that melanin

is a very tough chemical, and part of its function in hair and

feathers is to make them strong.

“This is why, when you get older, and like me your hair gets

grey, it actually gets weaker,” Mike explained. “But we’re not

detecting the presence of melanin by chemical means in fossils;

we’re doing it by physical means. It’s because it’s encapsulated in

these melanosomes.” Keratin – the protein of which hair and

feathers are made – is a plasticky kind of substance, so in order

for the melanin to get into it, it needs to be encapsulated.

Dr Jakob Vinther, a molecular palaeobiologist based in Mike’s

department at the University of Bristol, was the mastermind

behind the colour-identifi cation technique, in which diff erent

pigments, such as red, brown, buff , grey and black, are detected

simply by looking at the shape of melanosomes in the fossils

through a powerful electron microscope.

In modern birds, melanosomes that result in different

feather colours are diff erent shapes: although sausage-shaped

‘eumelanosomes’ contain the pigment ‘eumelanin’ and create

black plumage, the spherical ‘phaeomelanosomes’ contain ‘phae-

omelanin’, which creates orange plumage. These shapes are what

Jakob fi rst searched for in fossils of the early bird Confuciusornis

while he was a graduate student at Yale University.

In mammals, pigment is the common way to produce and

display a colour. Pigments in both plants and animals work by

refl ecting and absorbing diff erent wavelengths of light. White

refl ects all wavelengths of light, black absorbs all wavelengths

and colours in between selectively absorb some wavelengths but

not others. Chlorophyll, which makes plants green, for example,

absorbs all red light but refl ects green; anthocyanins, found in

red leaves, absorb green and blue light but refl ect red and yellow.

In 2013 a study that simulated the fossilisation process cast

some doubts over the reconstructions of dinosaur colour from

melanosomes. Dr Maria McNamara, a researcher then in the

same department as Jakob and Mike at Bristol, attempted to

mimic fossilisation by subjecting modern feathers to great

heats and pressures akin to those they might experience

underground in the Earth’s crust. “A brief spell in

an autoclave can reasonably simulate

the eff ects of temperature and

pressure over millions of

years,” she told Nature.

“Feathers are key to the

success of birds and we

can now dissect their

evolutionary history.”

Winged wonder.

Anchiornis was

among a number

of feathered gliding

dinosaurs that are

now known to have

had four wings.

Continued page 77

GETTY / JULIS CSOTONYI;

Anchiornis huxleyi

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