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Wednesday, April 2, 2008

Secret 'dino bugs' revealed

The X-ray techniques produce images with remarkable detail

It is like a magic trick - at first there is nothing and then it appears: a tiny insect unseen by any eye for 100 million years.

We are with Paul Tafforeau who is scrolling through images on his computer.

His pictures have been produced by a colossal X-ray machine that can illuminate the insides of small lumps of clouded amber (fossil tree resin).

As he plays with the settings, what starts out as grey nothingness suddenly becomes the unmistakable outline of a "wee beastie".

Who knows? This little creature could once have buzzed a dinosaur. It's certainly the right age.

Tafforeau is a palaeontologist. But whilst others of his profession will be in the dirt with a rock hammer and trowel, you'll find him at the end of one of the most remarkable "cameras" in the world.

The European Synchrotron Radiation Facility (ESRF) in Grenoble, France, produces an intense, high-energy light that can pierce just about any material, revealing its inner structure.

How the insects are illuminated

Tafforeau and colleague Malvina Lak have put kilos of opaque amber chunks in the way of this beam and have found a treasure trove of ancient organisms.

From more than 600 blocks, they have identified nearly 360 fossil animals. Wasps, flies, ants - even spiders. There are also small fragments of plant material. All of it caught up in the sticky goo of some prehistoric tree and then locked away until modern science provided the key.

Everything comes from the Charentes region in south-western France.



Electrons are fired into a linac, or straight accelerator. They're boosted in a small ring before entering the storage ring. The superfast particles are corralled by a train of magnets. Energy lost by turning electrons emerges as intense light (X-rays).

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Most of the organisms are minuscule. For example, one of the discovered mites measures just 0.8mm across. A fossil wasp is large by comparison at 4mm in length.

"The small size of the organisms is probably due to the fact that bigger animals would be able to escape from the resin before getting stuck, whereas little ones would be captured more easily," explains Malvina Lak, who is affiliated to the University of Rennes.

You can tell the ones that were trapped alive as opposed to the ones which must have been dead and blown into the goo. The live bugs were frozen with legs flailing. The dead, on the other hand, were encapsulated with legs curled up underneath them.

The ESRF synchrotron is using a quick-fire process to screen the ambers. First, block batches are loaded into the beamline and imaged using a high-contrast, high-resolution form of X-ray radiography.

This identifies the ambers that have interesting inclusions. These then undergo another session in the beamline which builds up 3D images of the trapped insects.

"Micro-tomography is based on radiography but instead of a single picture, we are taking pictures during rotation of the sample," explains Dr Tafforeau.

"For a complete rotation, we will take more than 1,000 radiographs - and from all these radiographs, we can reconstruct virtual slices; and after using a 3D processing tool, we 'extract' the specimen from the amber."

A plastic print would be deposited as part of the holotype, or reference

This virtual insect can be spun around on the computer screen. With resolution on the micron scale (millionths of a metre), fine anatomical details jump out.

But here's the really neat part. All that electronic information can be fed to a 3D plastic printer to make a physical model. A bug that in reality is less than a millimetre long and hidden inside a resin block then becomes a 30cm-long facsimile you can hold in your hand.

"In some ways it is better than having the real animal," says Dr Tafforeau, as he turns a giant plastic wasp in his palms.

The Charentes ambers are opaque - unless you have a synchrotron

"If you think about it, the real wasp is 4mm and to see it you would need a microscope; and if it's in opaque amber you need a synchrotron. Once it's done as a plastic print, you can see what you want."

The work is providing new insights into the ecology of Charantes in the Mesozoic Era. Many of the newly identified bugs are water-related: they would have lived around an esturine environment.

The translucent ambers gathered from the region had already indicated this; but the investigation of the opaque ambers at the ESRF has now strengthened this interpretation.

Paul Tafforeau, Malvina Lak and colleagues have high hopes for the techniques they are developing in the synchrotron.

In a paper to be published in the scientific journal Microscopy and Microanalysis, they suggest their work could form the basis of an alternative means of cataloguing new species trapped in amber.

Traditionally, every recorded organism will have a reference specimen, or holotype, deposited in a museum.

This specimen will be made available to any scientist who wishes to examine it or compare it with further discoveries.

But this presents a unique problem for insects caught in opaque amber. How do you deposit a reference you cannot see?

The ESRF team proposes that in future such holotypes be composed of the amber block, all the electronic data from the synchrotron and the 3D plastic print.

The type of work undertaken by Tafforeau, Lak and colleagues can only be done in a synchrotron; but it is time-consuming work.

Long-term, the ESRF hopes to upgrade its facilities. The improvements it plans are likely to open up many new avenues for "virtual palaeontology".

At the moment, the X-ray beam is no more than 4cm wide. An enhanced ESRF will be capable of producing a beam 25cm across - wide enough even to image the entire skull of a fossil human.

"We needed four days to scan 10kg of amber. With a larger beam and a wide-field detector, in four days we would be able to scan perhaps 100kg of amber; and with even better results," said Dr Tafforeau.

Original here

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