A multidisciplinary team of scientists at the Centre de recherche sur la paléobiodiversité et les paléoenvironnements (Muséum national d’Histoire naturelle, Paris/CNRS/UPMC), at the IPANEMA ancient materials research Platform (CNRS/MCC) and at the SOLEIL synchrotron have developed a new approach to study fossils. Using rare earth elements localization obtained at the Diffabs beamline and statistical methods, they can better describe the anatomy, fossilization environment and preservation. These results have just been published in Plos One and open new avenues for paleontological investigations.

The false colour overlay of iron (blue) and two rare earth elements (neodymium, red and yttrium, green), obtained using synchrotron X-ray fluorescence, reveals previously hidden anatomical details such as the skull and vertebrae from this Cretaceous fish ( 100 million years) (© MNHN/CNRS, Pierre Gueriau). Scale bar : 5 mm.

Due to compression and physico-chemical changes during fossilization, fossils interpretation is often very difficult. In rare specific context some fossils have been conserved in an exceptional preservation state, including “soft tissues” such as muscles or other organs. Nevertheless, their interpretation remains particularly difficult because of the limited contrast achieved using microscopy.

The study published in PLoS ONE displays a new non-destructive and non-invasive approach based on rare earth elements differential localization. These elements (yttrium, lanthanides and actinides) are known to be present in trace quantities in fossils, typically in the range of 1 to 1000 mg/g. Fast synchrotron- X-ray fluorescence imaging coupled to a statistical analysis of the images increases the contrast between the different preserved tissues. Such a vastly enhanced contrast arises from preferential elemental incorporation and allows discriminating the different fossilized anatomical structures.

Using this approach we imaged well-preserved fishes and shrimps from the Late Cretaceous of Morocco ( 100 million years). The contrasting elemental distributions greatly improved the discrimination of “hard tissues” (bones or carapaces) from both the sedimentary matrix and the “soft tissues”. Particularly, rare earth elements imaging reveals previously hidden anatomical features in a peculiar fossil fish, only know from a unique specimen. The technique also highlights bones hidden under a thin layer of rocks, then providing a direct observation of these structures even though manual preparation or virtual preparation using X-ray computed tomography are hardly applicable or impossible.

These new developments are likely to facilitate the interpretation of flattened fossils, which represent a large part of the paleontological collections. The thorough study of trace elements distributions open new avenues for paleoenvironmental studies and investigations on the long-term conservation processes (« taphonomy ») : the amounts reflect simultaneously the connectivity of the environmental water network, local physico-chemical conditions and properties of the mineral phases constituting the fossils.