Sunday, March 27, 2011

Organic material preserved in fossilized reptile skin

Fossilized organisms shared the same fate as the poor folk who dared to look at the mythical beast Medusa with their bare eyes: they were turned into stone. Most fossils that show evidence of soft body parts (i.e. not bones, shells, teeth and the like) are impressions, like natural plaster casts. The original material has either decayed away, or remains as an amorphous carbon film on the specimen.

Occasionally, well-preserved fossils show up which apparently preserve some trace of organic material. A specimen of reptile skin from the 50 million year old Green River Formation in Utah, USA, is one such candidate. Scientists using a sensitive, non-destructive method called Fourier transform infrared spectroscopy (FTIR) have showed that organic substances, which can be related to the original beta-keratin of the reptile skin, are present in the fossil.

The method is common in organic chemistry and the study of materials. Different chemical functional groups absorb a different characteristic set of wavelengths when exposed to infrared light. These patterns of absorption can be used to identify the groups. They showed that the fossilized skin had amide, thiol, and hydrocarbon groups which can be related to the products of beta-keratin (the thiol would come from cysteine bridges) and lipid breakdown. This was comparable to the results obtained from modern gecko skin. What's even more exciting is that when the detected levels of these chemical groups were mapped across a portion of the specimen, they revealed a pattern that corresponded to the visible scaly skin pattern of the fossil (below).

The authors of this study were careful in how they worded their statement. They said that "biological control on the distribution of endogenous organic components within fossilized soft tissue can be resolved," and not that "proteins are preserved in the fossilized skin." This is because the original proteins are no longer detectable (they tried to see if any protein could be isolated for sequencing), and the FTIR method only detects functional groups, not entire molecules.

What's particularly exciting about this, aside from the fact that we can still "see" the traces of ancient organic matter after 50 million years, is that this is a non-destructive method. The sensitivity also allows the mapping of information across the specimen, providing spatial information too. As one of the researchers told the BBC: "We have learned that some of these compounds, if the chemistry is just right, can give us a bit of a whiff of the chemistry of these ancient organisms." A very tantalizing whiff indeed!

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