Laser-Stimulated Fluorescence: soft tissue and skeletal detail revealed in micro and macro fossils

Abstract

Laser-Stimulated Fluorescence or LSF uses laser light to stimulate the fluorescence of fossil skeletons as well as the chemical signatures and morphologies of preserved soft tissues. This includes fluorescing specimens that are dark under UV light, backlighting carbon films, detecting unseen body outlines, revealing fake or composite fossils and detecting geochemical differences at the parts per million level. Since 2015, the use of LSF has produced many new and exciting discoveries. LSF clarified the countershading camouflage of the early horned dinosaur Psittacosaurus. It showed the wing configurations and footpads of the basal bird Anchiornis and the early short-tailed bird Confuciusornis. LSF images of Archaeopteryx specimens revealed the hidden quill of the first feather fossil and contributed to significant revisions of their phylogenetic codings. Among pterosaurs, LSF showed the shoulder bulk and hinted at the vasculature of the wings. It showed structural details of a fish eye that corroborate the lagerstaetten taphonomic model of the fossil deposit. LSF has been used to differentiate the parts making up composite specimens, helping to ensure their proper study. Rare specimens of egg shell have even been found on anthills by using LSF at night. Currently, new uses are being developed for histology to complement traditional white light and cross-polarised light microscopy as well as the potential to reveal ‘hidden’ soft tissues in the earliest life. In presenting past uses and results as well as on-going work, we intend to provide a platform for further methodological development and its popular utility by the palaeontological community.