X-RAY SYNCHROTRON IMAGING TECHNIQUES IN PALEONTOLOGY

After more than two centuries of scientific studies, fossils still have a lot of secrets to reveal. In many cases, external morphological investigations are insufficient, being both external and internal anatomical characters necessary in order to fully understand a fossil organism. Moreover, in other cases different scales of study have to be used, from the histological aspect to the general morphological one. Synchrotron based investigations enable very high quality 3D non-destructive X-ray imaging of a high diversity and disparity of fossils. These methods reveal fossil internal structures with incomparable accuracy and sensitivity. It therefore allows the study of fossils that cannot be investigated by conventional microtomography either due to a high degree of mineralization or low absorption contrast.

In the past few years, the rising of phase contrast synchrotron imaging techniques created a kind of revolution in non-destructive investigations of fossil samples, by revealing structures invisible with absorption based techniques. These techniques appears so powerful that nowadays about 90 percent of the scans performed at the ESRF on fossils are using propagation phase contrast effect, including the identification of insects trapped in opaque amber, dental developmental pattern of fossil hominids, imaging of microscopic fossils, research of embryos in ovo, histological analysis of vertebrates… More recently, thanks to the successful application of holotomography and the use of Paganin algorithm in the reconstruction of the 3D volumes has allowed the detailed imaging of dense and complex samples. This new improvement can bring even better data quality and new information about the samples than what was feasible with edge detection phase contrast. For example, its application lead to the discovery of the only fossil brain in the world, or allowed the study of sexual intercourse of fossil crustaceans. It appears nowadays as one of the most powerful and sensitive technique for non-destructive imaging on fossils, but technical possibilities offered by synchrotrons are evolving rapidly … especially within the time scale of paleontology.