Exceptionally preserved ‘skin’ in an Early Cretaceous fish from Colombia

Abstract

<jats:p>Studies of soft tissue, cells and original biomolecular constituents preserved in fossil vertebrates have increased greatly in recent years. Here we report preservation of ‘skin’ with chemical and molecular characterization from a three-dimensionally preserved caudal portion of an aspidorhynchid Cretaceous fish from the equatorial Barremian of Colombia, increasing the number of localities for which exceptional preservation is known. We applied several analytical techniques including SEM-EDS, FTIR and ToF-SIMS to characterize the micromorphology and molecular and elemental composition of this fossil. Here, we show that the fossilized ‘skin’ exhibits similarities with those from extant fish, including the wrinkles after suffering compression stress and flexibility, as well as architectural and tissue aspects of the two main layers (epidermis and dermis). This similarity extends also to the molecular level, with the demonstrated preservation of potential residues of original proteins not consistent with a bacterial source. Our results show a potential preservation mechanism where scales may have acted as an external barrier and together with an internal phosphate layer resulting from the degradation of the dermis itself creating an encapsulated environment for the integument.</jats:p>

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

“…4D) suggest that they are not consistent with the characteristics of biofilms, which tend to be amorphous and larger in diameter (Schweitzer, Moyer & Zheng, 2016). Blood vessels constitute one of the most promising microstructures preserved in fossil turtles for molecular paleontology studies, and future studies should focus on their molecular in situ characterization using ToF-SIMS mass spectrometry, similarly as it has been used in dinosaurs and other fossil vertebrates (Alfonso-Rojas & Cadena, 2020;Henss et al, 2013;Lindgren et al, 2018;Schweitzer et al, 2019).…”

“…Something in common to all aforementioned studies are the analytical tools used to study and characterize these fossil bone microstructures, which include principally: (1) ground sections and observation under transmitted and polarized microscopy ( Cadena & Schweitzer, 2012 ; Surmik et al, 2019 ); (2) bone demineralization using ethylenediaminetetraacetic acid (EDTA) as a chelating agent (0.5 M, pH 8.0), facilitating release the osteocytes-, blood vessels-, and any other cells- or soft-tissue fibers-like from the bone matrix for their posterior study by transmitted and/or polarized light, scanning and/or transmission electron microscopy and any coupled elemental analyzer, Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), immunological and antibody studies (e.g., Alfonso-Rojas & Cadena, 2020 ; Bailleul, O’Connor & Schweitzer, 2019 ; Bailleul et al, 2020 ; Cadena, 2016 ; Saitta et al, 2019 ; Schweitzer et al, 2013 ; Surmik et al, 2019 ; Wiemann et al, 2018 ).…”

The diagenetic fate of collagen as revealed by analytical pyrolysis of fossil fish scales from deep time

“…Several disparate explanations for the preservation of proteins in fossils from deep time have been proposed such as rapid mineralization leading to the incorporation of organic material into the mineral matrix (Schweitzer et al, 2005) stabilization resulting from iron chelation (Schweitzer et al, 2014) and the existence of a suitable microenvironment conducive to decay inhibition (Dhiman et al, 2021; Dutta et al, 2020). With increasing independent reports of endogenous protein/peptide preservation from Miocene (Boskovic et al, 2021), Eocene (Dutta et al, 2020), Cretaceous (Alfonso‐Rojas & Cadena, 2021; Bertazzo et al, 2015) and even Triassic fossils (Surmik et al, 2016) there may be a need for a re‐assessment of the potential for protein, or at least, residues from diagenetically altered protein (the “protein” and “collagen” after Collins et al, 1998), to be preserved in fossils, with emphasis on collagen. However, given that the preserved macromolecules are indicative of both their original structure, as well as the taphonomic conditions that led to their preservation (Briggs & Kear, 1993; Briggs & Summons, 2014), a study of collagen (and other proteins) in fossils, particularly from deep time, must incorporate not only identification of proxies that indicate their preservation, but also an investigation of the alterations undergone by the polypeptide sequence during diagenesis leading to the formation of a stable geomacromolecule, in order to provide a more accurate picture of the nature of their preservation.…”