Protein remains revealed in ancient reptile skin

24 March 2011 by Tamera Jones

Scientists have produced the first ever images of the residues of skin proteins still left in 50 million year old fossilised reptile skin.

Infra-red mapping

Infra-red mapping of the skin suggests how the sample was preserved.

The images show the residues sitting in the exact places in the fossilised skin that you'd find them in modern-day reptile skin.

The achievement is the result of scientists from two completely different disciplines of science - geochemistry and palaeontology - working together like they've never done before.

University of Manchester geochemists and palaeontologists worked together to produce the stunning infra-red images of the molecules called amides, which are only found in proteins. The sample came from 50 million year old rock from the Green River Formation in Utah, USA.

"If you compare these infra-red images with the same images of gecko skin, it's hard to tell the difference," says Dr Roy Wogelius from the University of Manchester, who led the research.

Until now, most palaeontologists would have assumed that these organic compounds probably came from bacteria. But the compounds the team found were dominated by material from the original organism.

Fossil reptile skin

Image shows exceptional preservation of the reptile skin (left), with close-up on the right.

Asked how the two disciplines came together, Wogelius explains: "One of my colleagues is a palaeontologist and he had this amazingly well preserved dinosaur skin, called 'dinomummy'. So I asked him if he was doing any spectroscopy on it. He looked at me as if I had two heads."

The two areas of science are so different, no-one had ever used infra-red mapping to analyse fossils before.

"This technique is perfect for identifying functional groups in proteins like we've got here," says Wogelius.

So he and Dr Phil Manning, also from the University of Manchester, decided to try infra-red spectroscopy on 'dinomummy' to see what they could find.

If you compare these infra-red images with the same images of gecko skin, it's hard to tell the difference.

Dr Roy Wogelius, University of Manchester

"We found skin proteins, but the rock the fossil was in just fell apart, so you couldn't map where in the dinosaur's skin these protein fragments were," says Wogelius.

In contrast, the new specimen came from much firmer rock that didn't fall apart.

"We found amides and it's also chock-full of trace metals, which tells us how these protein residues must have been preserved," Wogelius explains. "It was a real surprise to find that we could map the protein fragments. We expected a big mush."

When proteins start disintegrating, the breakdown products bind to minerals in the rock, which makes them stable and unlikely to get washed away by water. "The metals in the minerals anchor and protect the compound," says Wogelius.

Together with physicists at the Stanford Synchrotron Radiation Lightsource in California the researchers also made maps of the trace metals left in the reptile skin using new x-ray technology so that they could compare them what they saw with the infra-red images.

The maps and the images clearly show the protein fragments in the ancient reptile's skin.

The infrared and x-ray techniques have other advantages - you don't need to destroy the precious sample you're analysing to get a result. Most other techniques mean that scientists have no choice but to destroy the sample they're interested in analysing.

But for the technique to be successful, Wogelius explained that you need to know the history of museum samples.

"There's probably a lot more of this stuff in the fossil record than we imagined. So it's just a question of using the right techniques," says Wogelius.

The study is published in the Proceedings of the Royal Society B.

Infrared mapping resolves soft tissue preservation in 50 million year-old reptile skin - N P Edwards, H E Barden, B E van Dongen, P L Manning, P L Larson, U Bergmann, W I Sellers and R A Wogelius, Proceedings of the Royal Society B, published 23 March 2011, doi: 10.1098/rspb.2011.0135