Nothing but skin and bones: Anchiornis body outline revealed by laser fluorescence

Abstract

The outline of an animal is a fundamental expression of its biology, reflecting its gross anatomy and size. Fossilised body outlines provide invaluable constraints for reconstructing aspects from biomechanics to physiology, but are extremely rare to find. Even with exceptional soft tissue preserving fossils, prior studies have been hesitant to quantify body outlines because of imperfections arising from taphonomic processes. Using a new technique called laser-stimulated fluorescence imaging, high-definition soft tissues that are mostly invisible under white light conditions are revealed, greatly increasing the data available for body outline reconstructions. In this study, 229 specimens of the iconic Jurassic-aged ‘five-winged’ dinosaur Anchiornis huxleyi (Theropoda: Paraves) are surveyed and are shown to preserve exceptional details of the skin, patagial folds and footpads. In a first amongst dinosaurs, these data are used to reconstruct a quantitative high-detail body outline that confirms that the tail and legs were functionally decoupled and that the wing had close modern bird affinities, and reveals the body outline around the pubis for the first time. The imaging technique promises to reveal similar insights in other lagerstatten fossils and is facilitated by its low operational cost, rapid results and non-destructive nature.