Structure of the organic matter of conodont elements: atomic force microscopy data
The mineral composition of conodont elements is known in details; however their organic matter is studied in a less degree. The previous investigations had demonstrated that organic matter, consisting less than 4 % of a conodont element, was composed of collagen-like protein (Kemp, 1997, 2000, 2002; Rosseeva et al., 2011; Zhuravlev & Shevchuk, 2017). This work is aimed at characterizing of the structure of organic matter of the lamellar tissue of the Frasnian conodont element. The studied conodont element (CAI = 1, temperature of catagenesis <60 °C) was demineralized in 1N HCl, dried, and investigated with AFM (Ntegra Prima, NT-MDT, CKP «Geonauka», Syktyvkar). The organic matter of conodont element possesses globular, not fibrillary, nanostructured. The globules of 40-60 nm in size are ordered into linear (0.3-1.5 um wide) and isometric (200-260 nm) structures. Absence of any residues of fibrillar nanostructures, characteristic for collagen I and II, suggests either denaturation of collagen, or presence of non-fibrillar collagen (e.g. IV type of collagen). The observed nanostructures differ significantly from those of gelatins, thus denaturation of collagen is of low probability. The supposition, that collagen of conodont elements is non-fibrillar, is more probable. The conodonts demonstrate extremely specific biomineralization based on non-fibrillar collagen probably of epithelial origin. Thus vertebrate affinities of conodonts are not proved by study of the organic component of conodont elements.