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Colouring in the fossil past

15 March 2006

Morphos butterfly showing iridescent colours © Andrew Parker

Morphos butterfly showing iridescent colours © A Parker

Scientists have shown it is possible to determine the colour of animals that are extinct.

Prof Andrew Parker, scientist at the Natural History Museum, discovered that iridescent colours in animals result from tiny structures that show up under the microscope and these can be seen even in fossils of extinct animals.

Splitting sunlight
Diffraction grating showing fine parallel grooves reflecting light.

Diffraction grating showing fine parallel grooves reflecting light.

Iridescent colours, such as those on a morphos butterfly, are known as structural colours caused by reflecting optics.

Reflecting optics, like prisms, split sunlight into the colours of the spectrum. This is different from pigmented colours that are chemically-generated colours, similar to those in paints, found also in the skin, hair, or fur of animals.

Reflections on a shrimp
Seed-shrimp with one half of its shell removed

Seed-shrimp with one half of its shell removed

While studying seed-shrimps, crustaceans or 'insects of the sea', Andrew noticed a flash of green light coming from the creatures.

This iridescent colour was caused by diffraction gratings - a reflecting surface that has fine parallel grooves - the same as those you get on a CD. The diffraction gratings occur on the antennae of seed-shrimps, and are used to provide a light display during courtship. This was the first confirmed case of a diffraction grating in nature.

Visual effect of a diffraction grating in a seed-shrimp antennae © Andrew Parker

Visual effect of a diffraction grating in a seed-shrimp antennae © A Parker

True colours

Andrew could now look for signs of diffraction gratings in other animals and he found some in the 515 million-year-old Burgess Shale fossils - a community of marine animals that were buried in mud and preserved in extremely fine detail.

Diffraction gratings were found on the outer surfaces of three of the Burgess Shale species.

Community of Burgess Shale animals living 515 million years ago, showing colour. © New Scientist

Community of Burgess Shale animals living 515 million years ago, brought to life with colour. © New Scientist

The surfaces were reconstructed and these models were placed underwater and illuminated with the type of light that would have lit the Burgess Shale fossils 515 million years ago.

'I was looking at a scene of life, 515 million years old, depicted accurately in colour,' says Andrew.

Previously any colour given to the skin, feathers or fur of extinct animals was guesswork. Andrew's work allows a much truer representation of the colour of extinct animals and can be applied to other extinct creatures.

'A question that struck me was 'Why were animals at that time so colourful?' The obvious answer was that eyes existed then, which they did,' Andrew said.

'This set up other questions 'When did the first eye exist on Earth, and what happened when it did?' The answer to the latter, I was to discover, was exciting - the first eye triggered evolution's big bang.'

Andrew Parker's book Seven Deadly Colours is nominated for the 2006 Aventis Prize and is on sale in the Museum shop.

Parker's book In the Blink of an Eye, about the first eye triggering evolution's big bang, is also on sale in the shop and was selected as the subject for the 2005 Annual Physics Lecture at Stanford University (USA).

Dr Parker's work on the evolution of structural colours in ancient fossil animals won the 2005 silver L'ORÉAL Art and Science of Color prize.

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