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May 20, 2010

The Chemistry of Fossils

Most of the fossil evidence paleontologists analyze is what they can see. This is why so many of the fossil specimens are bones, shells, and other hard tissue: it's not as easy to decompose, so it preserves well in the fossilization process. However, soft tissue does sometimes preserve. Fossil feathers are a good example of this. The Burgess Shale fossils are another example. At a first look, these soft tissue fossils look like imprints on the rock. A new analysis technique reveals this isn't true, though. In exceptional soft tissue fossils, the imprint is also chemical.

The Thermopolis Archaeopteryx
Normal Color

The Thermopolis Archaeopteryx
False Color under Synchrotron

Using the Stanford Synchrotron Radiation Lightsource, at the Department of Energy's SLAC National Accelerator Laboratory, a team of paleontologists shot a focused beam of high-intensity X-rays at the Thermopolis Archaeopteryx specimen. Similar sorts of experiments had been run before: CT scans and low-intensity x-rays, for instance. However, these were not ideal to triggering and detecting the fluorescence of the chemicals in the fossils. The Sychrotron was. It efficiently formed a detailed scan of the fossil, and revealing an incredible secret of the fossil. At least a half-dozen different chemicals were found that aren't native to the rock or some fluke of the preservation process. These are trace elements from the animal itself! Of these elements, the most important of the findings was the high concentration of phosphorous in the feather imprints. Modern birds have a high phosphorous concentration in their feathers as well. This adds yet another thread to the tapestry of evidence tying birds and dinosaurs together. Original zinc and copper was found in the bones as well.

Close-up of the Archeopteryx
Color Scheme: Green- zinc;
Red- calcium; Blue- Manganese
So far, the synchrotron analysis technique has only been applied to the Thermopolis Archaeopteryx. Given the exciting results, though, I expect that other well-preserved fossils, such as the ones I mentioned earlier from the Burgess Shale, or even dinosaur skin impressions, could be analyzed this way. The chemical signature gives clues to evolutionary tracks, and may eventually help in determining other characteristics, like color, for creatures that haven't walked this planet for millions of years.

Source: Science News- Archaeopteryx Fossil Seen in New Light
Science Daily- X-rays Reveal Chemical Link Between Birds and Dinosaurs

Thanks to the Wyoming Dinosaur Center for the heads-up about this finding.