Applications of chemical imaging techniques in paleontology

Abstract

Chemical imaging techniques, based on a combination of microscopy and spectroscopy, are designed to analyse the composition and spatial distribution of heterogeneous chemical complexes within a sample. Over the last few decades, it has become an increasingly popular tool for characterizing trace elements, isotopic information and organic biomarkers (molecular biosignatures) found in fossils. Here, we introduce the analytical principle of each technique and the interpretation of the chemical signals, followed by a review of the main applications of these techniques in paleontology. We also demonstrate that each technique is associated with pros and cons, and the current limitations and obstacles associated with the use of each specific technique should be taken into account before being applied to fossil samples. Finally, we propose that, due to the rapid advances in the available technology and overall trends towards more multi-disciplinary studies in paleontology, chemical imaging techniques can be expected to have broader applications in paleontology in the near future.

The molecular evolution of feathers with direct evidence from fossils

“…Chemical Composition of Anchiornis Feather. We conducted ChemiSTEM analyses using an FEI Titan G2 series of Cs-corrected scanning/TEM (STEM) (26). We combined high-resolution elemental maps with detailed images of the ultrastructure of Anchiornis feathers and compared these with feathers from the four younger fossil specimens and a flight feather of Gallus (Fig.…”

Micro-XRF study of the troodontid dinosaurJianianhualong tengireveals new biological and taphonomical signals

“…S2g, S2h). A high level of Cu and Ni is also known in the feathers of many fossil and living taxa such as Anchiornis, Archaeopteryx, Gansus and other fossil and living birds [1,6,8,12,29,31]. In all these specimens and the specimen DLXH 1218, the Cu level is generally higher in the feathers than in the bones, and the copper concentration usually varies on different feather samples of an individual [6,12,29,31].…”

“…Morphological studies on the skeleton and the plumage have forged a solid link between non-avialan coelurosaurians and birds building a well-accepted framework to understand the dinosaur-bird transition [2][3][4]. Recent works started to look beneath the surface and into the ultrastructure and chemistry in fossil feathers and bones and bring our understanding of this major transition to another new level [1,[5][6][7][8][9][10][11][12]. Chemistry of exquisitely preserved fossil animals including several iconic flying/gliding capable theropods have been investigated to reveal information of their paleobiology and the fossilization process [1,6,9,10,[12][13][14].…”

“…Chemistry of exquisitely preserved fossil animals including several iconic flying/gliding capable theropods have been investigated to reveal information of their paleobiology and the fossilization process [1,6,9,10,[12][13][14]. Various chemical imaging techniques, e.g., Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray spectroscopy, and secondary-ion mass spectroscopy (SIMS)), have been employed to track the molecular, elemental and isotopic information [1,5,6,[8][9][10][11][12][13][15][16][17][18].…”

“…Unfortunately, previous studies all focused on non-destructive chemical imaging on small-sized specimens (e.g., Archaeopteryx, Confuciusornis) as limited by the analyzing instruments [6,8,11,12], or chemical analyses on small samples destructively taken from fossils [9,10,13,16,17]. So far systematic non-destructive chemical imaging on large-sized specimens of non-avialan dinosaurs have not been done.…”