Roy Wogelius unlocks fossils' secrets

This month we speak to a geochemist who has been unlocking the secrets held in the skin of a 50 million year-old fossilised reptile

Dr Roy A. Wogelius is among the first scientists to harness infrared methods for the analysis of fossils. Together with his colleague Dr Phil Manning, Roy has used the technique to visualise protein residues in the skin of a repltile fossilised over 50 million years ago. They also created the first ever element-specific maps of organic material in the fossilised skin.

What’s so special about fossilised reptile skin – what can it tell us?

In this case, we’ve learned that protein residue from 50 million year old reptile skin is not only present, but can be mapped to reveal original skin patterns. This is striking when we use infra-red to map the amide functional group derived from original skin keratin, but also when we map organic sulphur using x-rays. We also find that trace metal, in this case copper, reveals skin scale/hinge patterns, and this most likely is derived from the original pigmentation in the skin. Perhaps even more interesting, the subtle changes in the infra-red spectra of the fossil skin when compared to extant skin suggests that the breakdown products of keratin may form complexes which anchor the products to the underlying sediment, keeping the organics from being washed away and probably guarding them from further breakdown. So we have information not only about the survival of organic fragments, but about how they survived and also even a hint of remnant pigmentation.

How did you go about studying the skin, what exactly was the technology used?

We used a range of techniques, two of which we have been developing here at Manchester and in collaboration with the Stanford Synchrotron Radiation Light source.

Infrared mapping was used, for the first time in palaeontology to the best of my knowledge, to show the distribution of organic functional groups most likely derived from keratin in the skin. Full infrared spectra were also obtained and compared to the skin of a modern gecko. The similarity of the spectra and maps are striking. Perkin-Elmer graciously made equipment available to us free of charge. We also used Synchrotron Rapid Scanning X-ray Fluorescence (SRS-XRF) to map metals and sulphur in the fossil and in the gecko skin. We presented our first SRS-XRF data on the Archaeopteryx last year in the Proceedings of the National Academy of Sciences. One new feature of the maps presented in the reptile skin paper is that we were successfully able to map different oxidation states of sulphur, thus allowing us to distinguish between inorganic sulphate and organic sulphur. X-ray Absorption Near Edge Spectroscopy was used in tandem with the mapping to unequivocally show the presence of inorganic and organic species.

All of the above is non-destructive and gave us imaging information that had never been acquired for such ancient soft tissue before. However we also reluctantly performed some destructive analyses in order to support our argument that the organics were endogenous to the organism. Therefore, we did pyrolysis GC-MS of discrete samples taken from the skin, the sedimentary matrix, and from fossil plant material in the same geological formation. The reptile skin showed an organic inventory that was completely different from plant matter and from organic residue within the sediment- most of which is plant derived. It also showed that the reptile skin has not been reprocessed by aerobic microbes. We also performed glancing incidence x-ray diffraction analysis on the fossil bedding plane surface in order to determine which minerals were present.

Tell us about the element-specific maps you created – what can they tell us?

Because copper is typically chelated by melanin in skin, the copper map probably tells us about traces of pigment left behind in the reptile skin. Secondly, the ability to map organic sulphur as distinct from inorganic sulphur, lets us separate out inorganic precipitates and see, for the first time, the organic sulphur preserved within the skin of this 50 million year old creature. The organic sulphur mapped via SRS-XRF and the organic maps produced by infra-red agree with each other perfectly. The maps also give us an idea of how this skin might have been preserved. The diffraction analysis shows that important minerals with reactive surface sites are present in the sediment. Trace metals derived from the organism can attach onto these minerals. Importantly, some of the organic functional groups detected within the degraded skin can attach onto these metals as well, and so we think it is probable that the metals provide a bridge for these organic to anchor themselves onto the mineral substrate and thus keep them immobile over geological time. This anchoring may also protect the organic from further degradation. So the maps show biological patterning in organic compounds which has never been seen before, but also indicate how preservation might have occurred, and also just may give a hint as to pigmentation distribution.

How will all this information be used?

This gives us insight into how preservation occurs and how to look for exceptionally preserved organic material. It will reduce the need for destructive sampling in the future, and can be used in a range of scientific disciplines, including forensic science, biohazard disposal, studies of the origin of life, and even will be useful in predicting the mobility of radionuclides in radwaste repositories.

[caption id="attachment_23527" align="alignright" width="150" caption="Roy Wogelius"][/caption]

What’s next for you and this line of research?

We are pursuing the mapping of soft tissue structures in vertebrates, invertebrates, and even fossilized plant material. The combination of X-ray and infrared mapping and spectroscopy is providing a wealth of new results. Our next paper might have further surprises in store.

• A podcast interview with both Dr. Wogelius and Dr. Manning about the reptile skin results is featured on the Royal Society website and can be viewed by clicking here.