Molecular fingerprints resolve affinities of Rhynie chert organic fossils

Abstract

The affinities of extinct organisms are often difficult to resolve using morphological data alone. Chemical analysis of carbonaceous specimens can complement traditional approaches, but the search for taxon-specific signals in ancient, thermally altered organic matter is challenging and controversial, partly because suitable positive controls are lacking. Here, we show that non-destructive Fourier Transform Infrared Spectroscopy (FTIR) resolves in-situ molecular fingerprints in the famous 407 Ma Rhynie chert fossil assemblage of Aberdeenshire, Scotland, an important early terrestrial Lagerstätte. Remarkably, unsupervised clustering methods (principal components analysis and K-mean) separate the fossil spectra naturally into eukaryotes and prokaryotes (cyanobacteria). Additional multivariate statistics and machine-learning approaches also differentiate prokaryotes from eukaryotes, and discriminate eukaryotic tissue types, despite the overwhelming influence of silica. We find that these methods can clarify the affinities of morphologically ambiguous taxa; in the Rhynie chert for example, we show that the problematic “nematophytes” have a plant-like composition. Overall, we demonstrate that the famously exquisite preservation of cells, tissues and organisms in the Rhynie chert accompanies similarly impressive preservation of molecular information. These results provide a compelling positive control that validates the use of infrared spectroscopy to investigate the affinity of organic fossils in chert.

Optical photothermal infrared spectroscopy (O-PTIR): a promising new tool for bench-top analytical palaeontology at the sub-micron scale

“…Previous spectroscopic investigations of Rhynie Chert material provided important insights into the molecular preservation of its iconic fossils (Preston and Genge, 2009;Qu et al, 2015) and most recently have revealed that taxon-specific chemical fingerprints can be identified by ATR-FTIR spectroscopy (aperture size 100 μm; Loron et al, 2023). Here, we show that O-PTIR can resolve molecular differences within organisms and tissues at a much smaller spatial scale.…”

“…The middle layer shows an intense aliphatic absorption and strong ester C=O contribution. Finally, the inner layer, in the epidermis, is dominated by a high aliphatic absorption, contribution of ester C=O, C=O, carboxyl, carboxylate and N-moieties, attributed to condensation products of proteins and sugars (Wiemann et al, 2020;McCoy et al, 2021, Loron et al, 2023.…”

“…Bench-top techniques like micro-Fourier Transform InfraRed (micro-FTIR) and Raman spectroscopy have provided great insights into the molecular composition and preservation of key cellular components in both micro-and macrofossils (e.g., Marshall et Marshall, 2015;Wiemann et al, 2020;McCoy et al, 2020;Loron et al, 2022;2023) for resolution of several micrometres. Raman spectroscopy can achieve very high spatial resolution and provides complementary molecular information than FTIR but, with thermally mature organic material, is often limited to palaeothermometry (e.g., Baludikay et al, 2020).…”

Human brains preserve in diverse environments for at least 12 000 years

“…Mass spectrometric strategies for characterizing the nature and modification of protein-lipid [ 66 ], melanic [ 67 ] and metallo-molecular complexes [ 68 ] are well-established and provide a means to evaluate the crosslinked nature of preserved brains. In addition, non-destructive spectroscopic methods are well-suited for rapid, in situ characterization of molecular fingerprints [ 69 ] and their diagenetic alteration [ 41 ] in fossil organic matter, and constitute a valuable corroborative approach for precious, ancient samples. Finally, a range of largely X-ray-based methods might be employed to refine the identity [ 70 ], oxidation state [ 71 ], and tissue distribution [ 72 ] of metals and minerals intimately associated with preserved nervous tissues.…”

An evo-devo perspective on no Ordovician land plants

“…The ties to fungi are very tenuous, however, particularly when it comes to dispersed tubular maceralsnone of which possesses any tangible fungal synapomorphies. Niklas and Smocovitis (1983) considered macerated nematophytic thalli of Llandovery age to be conducting cells of a pre-vascular embryophyte, and a recent FTIR analysis of Nematoplexus from the Rhynie Chert (Loron et al 2023) indicated that the organic composition of this Devonian nematophyte reflected a land plant over fungal affinity. An evo-devo model of sporophyte assembly would predict that such isolated tubular macerals are some form of "proto" tracheary elements -apoptotic fluid-conducting cells.…”