Laser Fluorescence Illuminates the Soft Tissue and Life Habits of the Early Cretaceous Bird Confuciusornis.

Thomas G. Kaye,David A. Burnham,Zhonghe Zhou,Amanda R. Falk,Matthew Shawkey

doi:10.1371/journal.pone.0167284

Abstract

In this paper we report the discovery of non-plumage soft tissues in Confuciusornis, a basal beaked bird from the Early Cretaceous Jehol Biota in northeastern China. Various soft tissues are visualized and interpreted through the use of laser-stimulated fluorescence, providing much novel anatomical information about this early bird, specifically reticulate scales covering the feet, and the well-developed and robust pro- and postpatagium. We also include a direct comparison between the forelimb soft tissues of Confuciusornis and modern avian patagia. Furthermore, apparently large, fleshy phalangeal pads are preserved on the feet. The reticulate scales, robust phalangeal pads as well as the highly recurved pedal claws strongly support Confuciusornis as an arboreal bird. Reticulate scales are more rounded than scutate scales and do not overlap, thus allowing for more flexibility in the toe. The extent of the pro- and postpatagium and the robust primary feather rachises are evidence that Confuciusornis was capable of powered flight, contrary to previous reports suggesting otherwise. A unique avian wing shape is also reconstructed based on plumage preserved. These soft tissues combined indicate an arboreal bird with the capacity for short-term (non-migratory) flight, and suggest that, although primitive, Confuciusornis already possessed many relatively advanced avian anatomical characteristics.

Highlights

With the recent discoveries of magnificently preserved fossils from the Early Cretaceous Konservat-Lagerstatten (Jehol Biota) of northeastern China—many of which exhibit exceptional soft-tissue preservation, including plumage—a rare opportunity to study the soft-tissue anatomy of fossil birds arises
Laser-stimulated fluorescence (LSF) is a highly successful and versatile method that can be used to identify potentially modified fossils, highlight hidden structures, and, as this study shows, fluoresce soft tissues otherwise invisible under white light
Previous studies (e.g. [1,3]) visualized only the osteology and/or plumage of Confuciusornis, our study represents a first look at other soft tissues such as scales, dermal complexes, ligaments, tendons and musculature of Confuciusornis

Summary

Introduction

With the recent discoveries of magnificently preserved fossils from the Early Cretaceous Konservat-Lagerstatten (Jehol Biota) of northeastern China—many of which exhibit exceptional soft-tissue preservation, including plumage—a rare opportunity to study the soft-tissue anatomy of fossil birds arises. Modern birds have unique soft tissues that relate to their flight capability and preferred life habits. Modern birds possess both a propatagium and a postpatagium [10], which are expandable membranes on both the front and the back of the wing. Scales on the feet and tarsi can potentially be linked to life habit and evolutionary patterns [13, 14] These delicate soft tissue structures are rarely preserved in the vast majority of fossil birds; many specimens from the Lower Cretaceous Jehol Group are preserved with spectacular plumage and other soft tissues. LSF is a highly successful and versatile method that can be used to identify potentially modified fossils, highlight hidden structures, and, as this study shows, fluoresce soft tissues otherwise invisible under white light

Materials and Methods

Discussion