Illuminating the evolution of birds using Laser-Stimulated Fluorescence imaging

Abstract

Laser-Stimulated Fluorescence (LSF) is a geochemical imaging technique that instantly shows parts per million differences in mineral chemistry across fossil specimens. In revealing unknown anatomical and chemical information, LSF shows that fossils offer higher degrees of preservation than previously appreciated. In many cases, LSF fills important detection gaps showing data missed by more popular imaging techniques like synchrotron and UV. These strengths have allowed LSF to investigate important issues related to the evolution of birds. LSF has directly confirmed the expected form and function of the tail and legs of the early-diverging paravian Anchiornis and added data to its enigmatic volant capabilities by showing its narrow propatagia and unordered leading edge wing feathering. LSF has even detected feathering in perinate enantiornithines supporting their precociality and rediscovered the quill of the first described fossil feather, demonstrating that it is a new species. The preserved lateral body outline of the Early Cretaceous bird Sapeornis was revealed with LSF. For the first time, these soft tissue data were used to quantitatively improve the accuracy and reconstruction of its flight performance and style. The latter were further refined for the early-diverging pygostylian Confuciusornis, using its LSF lateral and ventral body outlines. In addition, LSF revealed a muscle-like propatagial ligament, unusually thick shoulders and a shallow chest profile in Confuciusornis that underscores the characteristics to fully consider when analyzing the early avian flight stroke and reconstructing flight performance. As a rapid, portable and low-cost technique, LSF promises to become a tool-of-choice in the study of avian evolution.