Wednesday, 28 September 2011

New Research Gives Insight Into The Colours Of Ancient Beetles

Insect fossils are comparatively rare as their weak exoskeletons can be crushed and therefore preservation is poor. However some fossil sites produce exceptional insect fossils. One such place is the Messel Pits in Germany. Fossils were preserved in highly anoxic conditions, away from intense pressure and heat under oil shale, perhaps the most favorable conditions for fossil formation. Indeed Ida, the 97%, early simian ancestor was discovered at Messel.

Perhaps less well known are the beetle fossils found at Messel. They are perfectly preserved in 3D with tiny details such as the delicate, articulated limbs. The most incredible feature, however, is a series of iridescent, striking colours that adorn the exquisitely fossilized carapaces. Analysis showed that these colours were not from the oil shale but came from microscopic, cellular structures within the shell which are responsible for the colours in arthropods.

These 50 million year old, blue beetles would have been more violet in life
Finally, we are able to see a prehistoric creature exactly as it would have been 50 million years ago, complete with colours. Yet recent research shows that these colours are in fact subtly different to those in life. Dr Maria McNamara of Yale University has shown that the fossilisation process causes slight warping of the melanin structure, causing the tonal value to change a few degrees towards the red and longer wavelength end of the the electromagnetic spectrum, in a process known as a redshift.

A research team led by Dr McNamara analysed the cuticles of various beetle specimens covering a range of dates from 47 to 15 million years old. The colours in the cuticles come from the aforementioned microscopic structures which absorb and enhance certain reflected wavelengths, causing a dazzling array of iridescent colours. The study used a series of powerful analytical tools to determine if warping during fossilisation had a significant enough effect upon the structures to change electromagnetic output.

The team's reconstruction of ancient beetle colours in life.
The beetle colour is taken and then shifted one
place to the left along the chain to reveal its true colours
They found evidence of a redshift which accentuated longer wavelengths. For example a beetle with green preservation would actually have been blue in life while a red beetle would have been green. 'What actually happens is - the refractive index of the cuticle changes,' explained Dr McNamara. 'This is a measure of how much the light is bent. This means the chemistry must have changed because the refractive index in a material will depend on what it's made from.'