NATIONAL PRESS RELEASE I PARIS I 28 JANUARY 2014
Decoding certain fossils thanks to rare earth elements
Until now, it was very difficult to read ‘flat’ fossils. A new approach to analysing such
fossils has just been developed by a team of researchers from the Ipanema unit (CNRS /
Ministry of Culture and Communication), the Paleobiodiversity and Paleoenvironments
Research Centre (CNRS / MNHN / UPMC), and the SOLEIL synchrotron. This nondestructive method is based on chemical elements called ‘rare earth’ elements: by locating
and quantifying traces of them, a better decoding of the morphology of fossils can be
obtained. This has allowed the scientists to describe not only the anatomy but also the
environment in which three fossils dating from the Cretaceous period were preserved. This
work was published in the 29 January 2014 issue of Plos One, and should facilitate the
analysis of many “flat” fossils, particularly exceptionally preserved ones.
During the fossilisation process, the remains of animals or plants are often flattened; compressed in two
dimensions under the pressure of sediments. This can sometimes create a real obstacle to the study of
such fossils. Another problem is that these crushed fossils undergo physicochemical changes during
fossilisation, which makes them more difficult to read. And yet these fossils can harbour a wealth of
information. In particular, when the anatomy is well preserved ('exceptionally preserved' fossils), soft
tissues such as muscle are fossilised. But locating these tissues is still difficult because of the limited
contrast achievable in optical microscopy and the limitations of tomography(1) , two techniques commonly
used to study fossils.
Scientists from the CNRS, MNHN, and the SOLEIL synchrotron have designed and developed a new nondestructive approach based on locating rare earth elements. These chemical elements (yttrium and
lanthanides) are known to be present in fossils in trace amounts: typically 1 to 1000 microgrammes per
gramme of matter. The quantity of trace elements incorporated at the time of fossilisation differs according
to the type of tissue. This preferential deposition provides a way to distinguish between the anatomical
parts of a fossil. It manifests itself by a major contrast between the different chemical elements according
to the type of tissue in the fossil when it is characterised using fast x-ray fluorescence imaging under
synchrotron radiation(2). To speed up the analysis, the team suggested a quick method of differentiating the
tissues, based on the probabilistic nature of the data measured.
1
Tomography is a technique based on reconstructing virtual sections of an object in three dimensions from a large number of radiographic images.
X-ray fluorescence is a secondary emission of x-rays by an atom bombarded with x-rays. The emission spectrum is characteristic of the chemical elements that
make up the sample. When used in imaging mode, it allows locating these elements. In this study, the very high intensity of the synchrotron source provides access to
the trace elements that are present, which cannot be reached with laboratory x-ray sources.
2
Scientists have applied this approach to three fossils (two fishes and one shrimp) found in Morocco. The
fossils date from the Upper Cretaceous era, approximately 100 million years ago. The contrasts obtained
allow hard tissues (bones or shells) to be distinguished from soft tissues (muscles or fossilised organs). In
particular, they revealed previously hidden anatomical details of a fossil fish known by a single specimen,
which has a skull bone shaped like a wide notched blade.
This new approach provides a detailed and precise view of the anatomy of a fossil without denaturing it
and without the need to finely prepare the sample in advance. It is particularly suitable for flattened fossils,
given that x-rays penetrate a few fractions of a millimetre inside the fossil. This technique has also
revealed certain bones hidden under a thin layer of rock, allowing them to be viewed directly. It has, for
example, made it possible to view certain hidden appendages of a fossilised shrimp, such as the legs and
antennae, which carry important information to study how it might be related to other types of shrimp.
Moreover, the rare earth content reflects the environment in which a fossil is preserved: connectivity to
environmental water networks, local physicochemical conditions and the properties of the mineral phases
constituting the fossils, which can therefore be better described.
This work should therefore facilitate the interpretation of the flat fossils that are very common in the fossil
register. It opens up fresh prospects for paleoenvironmental research and for a better long-term
understanding of fossilisation processes.
This research was carried out within the framework of the Ipanema platform, inaugurated on 12 September
2013 by Geneviève Fioraso, Minister for Research and Higher Education. Ipanema is a joint unit of the
CNRS and the Ministry of Culture and Communication, which was set up in partnership with the National
Museum of Natural History and assistance in particular from the SOLEIL synchrotron, which hosts it, and
the European Commission (FP7 CHARISMA project).
Image in false colours showing the distribution of iron (blue) and two rare earth elements
(neodymium in red and yttrium in green), obtained by synchrotron x-ray fluorescence
revealing hidden anatomical details of fossils such as the skull and vertebrae of this
Cretaceous fish, approximately 100 million years old.
© CNRS/MNHN, Pierre Gueriau.
Bibliography
Trace elemental imaging of rare earth elements discriminates tissues at microscale in flat fossils,
Pierre Gueriau, Cristian Mocuta, Didier B. Dutheil, Serge X. Cohen, Dominique Thiaudière, The OT1
consortium, Sylvain Charbonnier, Gaël Clément & Loïc Bertrand. Plos One, 29 janvier 2014.
Contacts
Scientist l Loïc Bertrand l T +33 1 69 35 90 09 / +33 6 81 33 28 23 l loic.bertrand@synchrotron-soleil.fr
Press CNRS l Priscilla Dacher l T +33 1 44 96 46 06 l priscilla.dacher@cnrs-dir.fr