A role for iron and oxygen chemistry in preserving soft tissues, cells and molecules from deep time

Abstract

The persistence of original soft tissues in Mesozoic fossil bone is not explained by current chemical degradation models. We identified iron particles (goethite-aFeO(OH)) associated with soft tissues recovered from two Mesozoic dinosaurs, using transmission electron microscopy, electron energy loss spectroscopy, micro-X-ray diffraction and Fe micro-X-ray absorption nearedge structure. Iron chelators increased fossil tissue immunoreactivity to multiple antibodies dramatically, suggesting a role for iron in both preserving and masking proteins in fossil tissues. Haemoglobin (HB) increased tissue stability more than 200-fold, from approximately 3 days to more than two years at room temperature (258C) in an ostrich blood vessel model developed to test post-mortem 'tissue fixation' by cross-linking or peroxidation. HB-induced solution hypoxia coupled with iron chelation enhances preservation as follows: HB þ O 2 . HB 2 O 2 . 2O 2 þO 2 . The well-known O 2 /haeme interactions in the chemistry of life, such as respiration and bioenergetics, are complemented by O 2 /haeme interactions in the preservation of fossil soft tissues.

Iron minerals within specific microfossil morphospecies of the 1.88 Ga Gunflint Formation

“…58). Post-mortem Fe mineralization of bone cells also occurs preferentially in/on walls59. Furthermore, pyritization of Gunflint microfossils similarly resulted of post-mortem Fe mineralization of microfossil walls and of the matrix surrounding microfossils (ref.…”

Mass Spectrometry and Antibody-Based Characterization of Blood Vessels from Brachylophosaurus canadensis

“…40,41 PIH-treated B. canadensis and 10% formalin fixed ostrich blood vessels were embedded in LR White resin blocks after partial dehydration in 70% ethanol. Six to eight 200 nm sections were taken on a Leica EM UC6 ultramicrotome and dried overnight at 45 °C to each well of a 6-well Teflon-coated slide (Electron Microscopy Sciences).…”

Role of Sediment Size and Biostratinomy on the Development of Biofilms in Recent Avian Vertebrate Remains

“…Despite previously proposed alternative hypotheses for the presence of primary soft-tissues in Mesozoic vertebrate fossils, such as contaminants or recent biofilms (Kaye et al, 2008), an abundance of biomolecular evidence has confirmed their initial interpretations as primary soft-tissues (Schweitzer et al, 2005(Schweitzer et al, , 2009(Schweitzer et al, , 2016Asara et al, 2007). Biochemical processes have been proposed to play a significant role in the preservation of soft osteological tissues; recently iron has been suggested as an alternative mechanism to explain the process by which primary soft-tissues can remain pliable over geologic time, by which iron from hemoglobin serves as a natural chelator to increase tissue immunoreactivity in vertebrate remains (Schweitzer et al, 2014;Lee et al, 2017). However, the presence of mineralized biofilms in vertebrate samples were osteological soft-tissues have also been recovered suggests a role in tissue preservation (Briggs, 2003;Peterson et al, 2010;Kremer et al, 2012;Raff et al, 2013Raff et al, , 2014Schweitzer et al, 2016), where biofilm crystallization in Haversian and Volkmann's canals seals natural vectors from further microbial penetration and retards subsequent metabolization of soft-tissues.…”

“…Furthermore, iron has also been previously associated with soft-tissue preservation and biofilms and interpreted as pyrite framboids (Kaye et al, 2008;Peterson et al, 2010). The presence of iron associated with both preserved soft-tissues and mineralized biofilms suggests that multiple mechanisms may be involved in the preservation of primary biomolecules in fossil vertebrates (e.g., Kaye et al, 2008;Peterson et al, 2010;Schweitzer et al, 2014), including depositional chemistry, biostratinomy and sediment grain size. In order to fully explain the complex processes required to preserve primary soft-tissues in vertebrate remains over tens of millions of years, further analysis and actualistic taphonomic experimentation of biochemistry, geochemistry, and paleoenvironmental factors are needed.…”