In situ SEM/EDS compositional characterization of osteocytes and blood vessels in fossil and extant turtles on untreated bone surfaces; different preservational pathways microns away

Abstract

Osteocytes and blood vessels are the main cellular and tissue components of the bone tissue of vertebrates. Evidence of these soft-tissue microstructures has been widely documented in the fossil record of Mesozoic and Cenozoic turtles. However, all these studies have characterized morphologically and elementally these microstructures via isolation from the fossilized bone matrix where they were preserved or in ground sections, which could raise skepticism about the results due to potential cross-contamination or reagents effects. Fossil turtle bones from three different localities with distinct preservation environments and geological settings, including Mongolemys elegans from the Late Cretaceous of Mongolia, Allaeochelys crassesculpta from the Eocene of Germany, and a podocnemidid indet. from the Miocene of Colombia are studied here. Bone from two extant turtle species, Lepidochelys olivacea, and Podocnemis lewyana, as well as a commercial chicken Gallus gallus were used for comparisons. Scanning Electron Microscopy-Energy Dispersive Spectroscopy analyses performed directly on untreated fresh surfaces show that osteocytes-like in the fossil turtle bone are mostly composed of iron and manganese. In contrast, the in situ blood vessels-like of the fossil turtles, as well as those from the extant taxa are rich in elements typically organic in origin (carbon and nitrogen), which are absent to minimally present in the surrounding bone or rock matrix; this suggests a possible endogenous composition for these fossil structures. Also, the results presented here show that although originally both (osteocytes and blood vessels) are organic soft components of bone as evidenced in the extant turtles and chicken, they can experience completely different preservational pathways only microns away from each other in the same fossil bone.

A Chemical Framework for the Preservation of Fossil Vertebrate Cells and Soft Tissues

“…In-situ polymerization of proteins and DNA via the formation of radical intermediates is well known to occur within biological systems exposed to transition metal catalysts (Roberfroid & Calderon 1995). Additionally, substantial amounts of goethite have been reported associated with the OSTs (osseous soft tissues) of ancient vertebrates (Boatman et al 2019;Cadena 2016;Cadena 2020;Kaye et al 2008;Schweitzer et al 2014;Surmik et al 2016). This supports the hypothesis that at some point post-mortem the tissues encountered redox-active iron which could have functioned to catalyze in-situ polymerization.…”

“…The newly formed radical biomolecule can then react through one of several mechanisms with neighboring biomolecules to form intermolecular crosslinks (Catalá 2010;Roberfroid & Calderon 1995). The hypothesis of redox-active iron as a catalyst for this radical mechanism was supported by numerous reports of the presence of iron oxides, specifically goethite, in association with fossil vertebrate soft tissues (Boatman et al 2019;Cadena 2016;Cadena 2020;Kaye et al 2008;Schweitzer et al 2014;Surmik et al 2016).…”

“…A growing number of studies have reported the recovery of cells and other soft tissues within ancient vertebrate remains, including those of dinosaurs (Armitage & Anderson 2013;Boatman et al 2019;Cadena 2016;Cadena 2020;Lee et al 2017;Lindgren et al 2018;Lindgren et al 2011;Manning et al 2009;Schweitzer 2011;Schweitzer et al 2007;Schweitzer et al 2005;Schweitzer et al 2013;Schweitzer et al 2009;Surmik et al 2016) (Figure 1(A-B)). These reported soft tissues initially generated controversy within the field of vertebrate paleontology and were challenged as being exogenous biofilms (Kaye et al 2008;Saitta et al 2019).…”

SEM Analyses of Fossilized Chondrocytes in the Extinct Birds Yanornis and Confuciusornis: Insights on Taphonomy and Modes of Preservation in the Jehol Biota

“…In Confuciusornis, chondrocytes were alumino-silicified and the decayed softtissues were apparently both alumino-silicified and ironized (most likely by diagenetic precipitation of iron oxides) (Figures 3, 4). This shows that processes of cellular and soft tissue preservation can be different within the same fossil, and demonstrates once again that the chemistry of different fossilized structures that are microns away can be quite different (e.g., see Cadena, 2020).…”

Primary synovial chondromatosis: an elemental investigation of a rare skeletal pathology

“…Specific elements can be identified by their signature X-ray energy levels released as specimen electrons move to lower energy level orbitals. The utility of SEM-EDS is well-represented in various fields of biology, including forensic anthropology [17], dentistry [18], bioarcheology [19], and biomedical research [20]. Despite its widespread applications in biological research, to the knowledge of the authors, the utility of SEM-EDS has yet to be leveraged in the elemental investigation of intraarticular loose bodies, including those caused by PSC.…”