Imaging techniques and the remote study of fossil plants

International audienceNew imaging techniques are increasingly facilitating the remote study of fossil plants, providing access to researchers unable to visit collections while avoiding the transport of material that is often unique and/or fragile. This talk will present some of these techniques, with examples of uses during recent years when access to laboratories and collections was restricted due to the Covid-19 pandemic. Photographing fossil plants classically requires time and an experienced observer, able to identify and capture all the morpho-anatomical details needed to characterize the specimen at different scales. This process is now greatly facilitated by digital microscopes that allow any user to capture, in a single Step, a very high resolution, fully focused image of a whole specimen or préparation. This image can then be shared and used by anyone to study the fossil’s features remotely. To illustrate the level of detail available to a remote observer, we will present digital microscope photographs of several Palaeozoic to Cenozoic fossils, including compressions with preserved anatomical details, reproductive structures in amber, and polished surfaces and thin-sections of permineralized specimens. In the specific case of fossil plants preserved as adpressions, theoriginal morphology and 3D Organization of a specimen can be reconstructed by studying slight topographical details. To reveal them, the observer needs to use various light directions and angles, a process that cannot be easily replicated using classical photographs.Réflectance Transforming Imaging (RTI), a method developed in archaeology and more recently applied to fossil material, produces photographs in which the angle of the light can be changed at will. This allows the remote inspection of the specimen’s surface 3D structure.We will show how we used this technique to reinvestigate the type specimen of Gingkophyllum grassetü, a putative ginkgophyte from the early Permian of France