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Beetle Find Is One of the Oldest Colored Fossils

John Pickrell in England
for National Geographic News
August 18, 2003
 
Paleontologists are used to drab brown and gray fossils. Sediments that seep in to cast the shape of ancient organisms in stone, determine the color. Instead, long-gone beasts and the ancient worlds they inhabited, spring to life in the depths of these scientists' imaginations.

Now under exceptional circumstances, scientists have uncovered and explained a 50-million-year-old beetle fossil that still retains the bright blue metallic hue it sported in life. This beetle and others from the same site, are very rare examples of fossils that retain any original color, and are the oldest colored fossils ever found.


The specimen is a "paleontological Rosetta stone" said Andrew Parker, lead researcher behind the find, and evolutionary biologist at the University of Oxford in England. The fossil beetle may be the key to analyzing and predicting the color of other well-preserved invertebrate fossils, fish scales and even bird and dinosaur feathers, that have not retained any original coloration, he said.

Exceptional Preservation

The beetle specimen was found in 50-million-year-old oil shale deposits from the Messel Quarry near Frankfurt, Germany. Messel, a World Heritage site, is unique because its fossils are so well preserved. Bats and crocodiles for example, not only retain skeletal parts, but outlines of their entire bodies. The beetles are unusual in that they still contain the original material—chitin—that formed their exoskeleton in life.

Messel fossil hunters had previously turned up beetles, which retained bright colors lost on drying, but those researchers had paid little heed to color before. "Plenty of people are working on color in animals today, but few have thought of looking at colors in the past," said Parker.

Parker, and physicist colleague David McKenzie of the University of Sydney, are the first to detail these colored beetles and explain why they have retained their decoration over so many millennia. The pair describe the remarkable find in a recent online edition of the journal Biology Letters.

Coloration is one of the very many speculations that researchers, filmmakers and alike, have to make when reconstructing prehistoric plants and animals. When organisms become fossilized, the original material of their body is usually completely replaced. "In this process, chemicals are destroyed and pigments are not retained," said Parker.

World of Color

However there are ways, other than chemical pigmentation, in which organisms can produce color. One way is using a structure, such as wafer thin stacks of thin translucent organic material, to interfere with and reflect light (in a similar way to a prism splitting white light into colored beams). These films, made of chitin for example, can reflect and amplify light of one wavelength (or color). This is how most iridescent or metallic animal colors are produced, such as those striking hues found to adorn shiny butterfly wings, the feathers of hummingbirds and peacocks, and an entire rainbow of beetles.

Microscopic analysis revealed that the exoskeleton of the beetle found at Messel did indeed retain a type of structure known as a multi-layer reflector in its chitin exoskeleton, thus explaining its color.

"There is an incredible level of preservation in these [beetle] fossils," commented Chris Lawrence senior scientist studying the physics of biological color and its application, at research and development company QinetiQ in Hampshire, England. Finding colored fossils is unheard of, he said.

This is the first time that a multi-layer reflector has been found in a fossil, and the find may have wider implications, said Parker. It could pave the way for predicting the color of other well-preserved fossils that no longer retain original hues, but still carry the fine shape of once-translucent, color-producing structures. Computer models could then be used to predict the wavelength of light, or color, that would have been reflected back from these structures in life.

To prove that point, Parker and McKenzie prepared a slice of the fossil and examined it under a powerful electron microscope. They measured the dimensions of the multi-layer reflector and fed those details into a computer program. The results were encouraging. Using those measurements alone, the computer program predicted that a bright blue hue would be produced.

Painting the Past

That result proves that the method could be accurately used to measure other exceptionally well-preserved fossils containing similar color-producing structures. These would most likely be other types of invertebrate shell, but could include anything from iridescent reptile skin to iridescent bird feathers—and even feathers of dinosaur relatives, said Parker. Extinct and numerous trilobites—flattened oval-shaped, lobster-like animals—might be one obvious contender, he added.

Data on ancient color could tell us about the environment and behavior of animals. Coloration is important for mating, camouflage, and intimidation, said Parker.

Predicting the color of other fossils is quite plausible, agreed Lawrence, but will depend on the type of substrate. Fine clays and amber would be ideal, but the grains of sandstone, for example, would be so large as to obscure the structure, he said. Learning about the evolution of structural color could provide us with insight for commercial applications, he added.

Parker has already used the computer methods to predict the color of some very ancient 515-million-year-old fossils, but until now he had no idea whether the method was accurate or not. These weird-looking animals, unlike anything known today, may have sported a hologram type sheen, which changed color depending on the angle of view, said Parker.

For further information, read: In The Blink of An Eye (2003) by Andrew Parker, published by Perseus Books.
 

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