Combined microscopy and spectroscopy techniques to characterize a fossilized feather with minimal damage to the specimen

The study of fossil feathers has been revitalized in the last few decades and has contributed significantly to paleontological studies of dinosaurs and birds. Specific morphological and physicochemical characteristics of the microscale structures of feathers and the protein keratin are key targets when preserved during the fossilization process. Keratin is a fibrous protein that composes some hard tissues such as hair, nails and feathers. It is part of the so called intermediate filaments inside keratinocyte cells and is rich in sulfur containing amino acid cysteine. To date, different microscopy and analytical methods have been used for the analysis and detailed characterization and classification of feathers. However, in this work we showed that analytical optical and electron microscopies can be quick and precise methods with minimal effects on the sample during analysis. This association of different approaches on the same sample results in correlative data albeit in different length scales. Intracellular bodies called melanosomes originally present in melanocyte cells were identified with Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), and had well-defined orientation and a mean aspect ratio comparable to melanosomes extant in dark feathers. The detection of sulphur in melanosomes via Energy Dispersive Spectroscopy both in SEM and TEM shows that, along the fossilization process, sulphur from the degraded keratin matrix could have been trapped inside the melanosomes. Chemical groups that make up keratin and melanin in the fossil sample were detected via FT-IR Spectroscopy and Confocal Laser Scanning Microscopy (CLSM). The use of combined analytical microscopy techniques can contribute significantly to the study of fossils generating precise results with minimum damage to the original sample.