Exceptional preservation of organic matrix and shell microstructure in a Late Cretaceous Pinna fossil revealed by photoemission electron spectromicroscopy

Abstract

We present evidence of exceptional preservation in the nacre and prismatic layers of a 66 Ma bivalve shell using photoemission electron spectromicroscopy (PEEM). PEEM is a novel method to assess in situ the quality of mineralogical and organic preservation. The analysis is non-invasive and non-destructive, providing spatially explicit maps of microstructure, organics and mineral components, and the crystallographic orientation in mollusk shells. Comparison of a Late Cretaceous and a modern shell demonstrates that the 66 Ma shell (1) preserves original aragonite and calcite crystals in nacre and prismatic layers, respectively, (2) maintains nearly identical mineral microstructure and crystal orientations, and (3) preserves interprismatic proteins. Remarkably, interprismatic proteins are preserved with intact peptide bonds, and suggest an abundance of the amino acid glycine. These findings in a 66 Ma shell support the exceptional quality of organic preservation documented here, which may prove to be relatively common among fossil shells that preserve nacre. PEEM analysis is useful for understanding taphonomic processes influencing shell and molecular fossil preservation over geologic time scales, and contributes to our knowledge of molluscan physiology, biomineralization, evolution, and diagenesis.

Biomineral armor in leaf-cutter ants

“…The mineral-cuticle interface of Acromyrmex echinatior was investigated using X-PEEM at the Advanced Light Source (Lawrence Berkeley National Laboratory, Berkeley, CA) (Fig. 2b ) 35 . Distinct X-ray absorption near-edge structure (XANES) spectra occur at the carbon K-edge for each of three regions: cuticle, epicuticle, and mineral layer (Fig.…”

“…After final polishing, the samples were rinsed with ethanol and gently wiped with TexWipe Cotton (Texwipe, Kernersville, NC), air-dried, and coated with 1 nm Pt on the areas to be analyzed and 40 nm Pt around it 51 . For C K-edge spectra, PEEM stacks were acquired by scanning across 280-320 eV range with 0.1-eV step between 284 and 292 eV, and 0.5-eV step elsewhere, resulting in 145 images per stack 35 . For O K-edge spectra, PEEM stacks were acquired by scanning across 525-555 eV range with 0.1-eV step between 530 and 545 eV, and 0.5-eV step elsewhere, resulting in 181 images per stack 52,53 .…”

“…For C K-edge spectra, PEEM stacks were acquired by scanning across 280–320 eV range with 0.1-eV step between 284 and 292 eV, and 0.5-eV step elsewhere, resulting in 145 images per stack 35 . For O K-edge spectra, PEEM stacks were acquired by scanning across 525–555 eV range with 0.1-eV step between 530 and 545 eV, and 0.5-eV step elsewhere, resulting in 181 images per stack 52 , 53 .…”

A Decrease to Low Carbonate Clumped Isotope Temperatures in Cryogenian Strata

“…Rock‐buffered alteration through burial could include dissolution and reprecipitation or occlusion of microporosity (e.g., Moshier, 1989; Staudigel & Swart, 2019), even with the interpreted early lithification and shallow diagenesis for these dolomites. Criteria for recognizing diagenetic alteration in micritic carbonates are more ambiguous than fossil material (e.g., Gilbert et al, 2017; Myers et al, 2018; Wenzel et al, 2000). Comparison of preglacial and glacial dolomite isotopic compositions provides insight to the extent of alteration experienced by glacial strata and their potential to preserve δ 18 O values from their early lithification and diagenesis.…”

First sequencing of ancient coral skeletal proteins

“…Thus, these invertebrate biomineralization proteins provide a potential sequencing target. For corals, such proteins become embedded in individual skeleton crystals 13 , protecting them from degradation for long periods of time, and nitrogen likely derived from biomolecules in invertebrate biominerals has been analyzed for isotopic composition and presence of peptide bonds in invertebrate samples tens to hundreds of millions of years old (e.g., 14 – 17 ). For instance, δ 15 N analyses of coral skeletons from the Triassic reveal that amino acids are preserved in fossil corals for hundreds of millions of years 15 , nearly as long as there have been reef-building scleractinian corals 18 .…”