Biomineral electron backscatter diffraction for palaeontology

Abstract

Electron backscatter diffraction (EBSD) originated in materials science and has transferred to biomineral research providing insight into fossil and modern biominerals. An electron microscopy technique, EBSD requires a fine polished sample surface where the electron beam diffracts in the first few lattice layers, identifying mineral, polymorph and crystallographic orientation. The technique is particularly well suited for the analysis of modern and fossil calcium carbonate biominerals, where it provides key insight into biological control of mineral formation such as in molluscs and brachiopods. EBSD readily identifies original and secondary mineralogy, which helps to inform our understanding of biomineral evolution such as the identification of original aragonite in Silurian trimerellid brachiopods. As a technique to identify and thus avoid the inclusion of secondary minerals in proxy organisms such as corals, EBSD can be used to ensure accuracy of palaeoproxy data. Even when fossil systems have no modern equivalents, EBSD can provide key data to determine functional mechanisms such as in the lenses of schizochroal eyes of phacopine trilobites. These few examples illustrate that EBSD is proving to be a valuable component of the palaeontology toolkit.

Electron backscatter diffraction (EBSD) analysis of maniraptoran eggshells with important implications for microstructural and taphonomic interpretations

“…, ). It is also widely applicable in studies on palaeontological and neontological biomineralization, especially in carbonate biominerals (Cusack ; Pérez‐Huerta et al . ).…”

“…). In general, vertebrates utilize calcium phosphate as the building blocks of their internal skeleton whereas invertebrates use calcium carbonate for their shell construction (Cusack & Freer ; Cusack ; Athanasiadou et al . ).…”

“…). Biomineralization studies using EBSD have been mainly concentrated on invertebrates such as bivalves, brachiopods, corals and trilobites (Cusack , and references therein). However, EBSD can also be extensively applied to calcium carbonate biominerals found in the sauropsid vertebrates: namely, their eggshells.…”

Distinguishing Biologically Controlled Calcareous Biomineralization in Fossil Organisms Using Electron Backscatter Diffraction (EBSD)

“…For a more detailed description about the method, see Prior et al (1999). For a discussion of applications to biological specimens, see e.g., Griesshaber et al (2010) and Cusack (2016).…”

Enigmatic encrusting fossils from the Upper Devonian of Russia: probable Rothpletzella microproblematica preserved in three dimensions

“…Päßler et al (2018) documented poorly ordered, weak parallel arrangement of crystals with a nearly random distribution of misorientation angles between adjacent crystals. Such a texture is less ordered and less diagenetically stable than more constrained crystallographic textures of metazoans (Griesshaber et al 2010;Cusack 2016;Päßler et al 2018). Poorly ordered structure might have resulted in the relative instability of Rothpletzella skeletons and its potential dissolution in conditions of low redox potential.…”