2000 IRISH SCIENTIST YEAR BOOK

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Fabulous fossil frogs

National University of Ireland, Galway
Patrick J. Orr

Fifteen million year frog from northeastern Spain in which the body outline is preserved as a film of fossilized bacteria.

Nature is a great recycler, and therefore the history of life on Earth as revealed by the fossil record is incomplete. The 'hard parts' of organisms - i.e. biomineralized tissues (for example shells, bones and teeth) - are much more readily preserved than decay-prone 'soft tissues' such as muscles and internal organs. Exceptionally-preserved fossils, those in which these soft tissues are present, are very rare in the geological record, reflecting the very specific chemical conditions, and depositional settings, that are necessary for their preservation. Exceptionally preserved fossil biotas are a major focus for research worldwide as they provide palaeobiologists with a more complete picture of the biology of individual organisms. Secondly, as now, the vast majority of organisms in the geological past would have lacked biomineralized tissues, thus these biotas allow more accurate reconstructions of the ecology of fossil communities.

Research by Dr Patrick J. Orr, of the Department of Geology, NUIG, has shed new light on the processes by which fossils are exceptionally preserved in the fossil record. Study of fifteen million year old frogs from northeastern Spain has revealed that, in addition to the skeleton, soft tissues such as the skin, muscles and eyes are preserved (see Figure). These soft tissues are preserved in small (1mm diameter) spheres of calcium phosphate that represent fossilized bacteria. These bacteria formed a bacterial mat or biofilm over the surface of the decaying frogs: preservation of the bacteria ensured that the outline of the frog was replicated.

These results confirm the importance of bacterially-mediated precipitation of minerals preserving the soft tissues of fossils, but the research also has wider implications. The ability of bacteria to sequester metals from solution has potential in the bioremediation of polluted aqueous systems. Identifying how terrestrial microbes are preserved can contribute to more rigorous analysis of the case for (or against) extraterrestrial life such as putative Martian microbes.

Contact: Dr Patrick J. Orr,
Department of Geology,
National University of Ireland, Galway;
Tel: +353-(0)91-524411, ext. 2351;
http://alisanos.nuigalway.ie/paddy.html
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