*Read original study online at http://fluoridealert.org/wp-content/uploads/barthel-2020.pdf


Fossil bones represent valuable paleontological archives for reconstructing the paleobiology and -environments of vertebrates throughout geological time and thus also represent an important window into the evolution of life on Earth. The preservation of organisms or parts of them over long geological timescales requires exceptional conditions before and after death of the organism. During diagenesis, the remains are affected by various chemical processes like dissolution or pseudomorphosis, so the original material, especially the organic soft tissue, is often lost or severely modified. However, a detailed understanding of the preservation and fossilization of bone at the microscopic scale is still lacking. This is partly because bone is a complex hierarchical composite material. It consists of a nano-crystalline, hydrated, hydroxylated, and carbonated calcium phosphate phase (hydroxylapatite (HAp)-like) that is embedded in a fibrous organic matrix of predominately collagen and subordinately lipids. A recent vibrational spectroscopic study [1] suggested that molecular water is a stabilising component of biogenic apatite (bioapatite), which has also been postulated in previous studies based on nuclear magnetic resonance spectroscopy [2]. Pasteris et al. [1] proposed that the chemical formula of bioapatite should be Ca10–x[(PO4)6–x(CO3)x] (OH)2–x · nH2O, where n ? 1.5 and x ranges between 0.1 and 0.3. The OH group in bioapatite can be replaced by F, whereas Ca may partly be substituted by, e.g., Mg, Zn, Sr, Na, and K [3]. Fluorine was found of particular importance for the preservation of bone and teeth during diagenesis [4, 5] as well as for caries prevention by transforming HAp to more stable, i.e., less soluble fluorapatite (FAp) [6]. Bone apatite is thus a complex solid solution that occurs as nano-crystals with sizes in the order of 20 to 150 nm. Due to its crystal-chemical properties, bioapatite is a highly reactive phase that, if its physicochemical environment is changing (for instance, after death of the organism), has a high thermodynamic driving force to dissolve [4] or to react in aqueous solutions that are (super)saturated with respect to apatite. Under certain conditions original bone tissues survive over geological time scales, includingorganic components (e.g., collagen) that could still be detected in dinosaur bone [7, 8]. Such bone specimens are often characterised by a larger average crystallite size, a higher crystallinity, and a different apatite chemistry with respect to the original bone [9–12].

The entrapment of an organism in viscous tree resin is a unique prerequisite in terms of fossilization, with the chance to preserve embedded organisms in a three-dimensional, life-like posture. In public perception, amber is therefore often referred to as a “time capsule,”prohibiting the majority of decay processes. Amber represents a strong taphonomic filter and favors the conservation of small organisms such as insects and spiders, which are often extremely well preserved with ultrastructural detail [13, 14, 15]. The liquid resin initially protects entrapped organisms from microbial attack and predators, which represents an important basis for preservation. However, evidence has been reported showing that even air can pass through amber, which may cause oxidation reactions [16]. In general, it is well known that the preservation of fossils in amber differs largely throughout specimens and amber deposits. The degree of preservation ranges from the relict occurrence of straight chain hydrocarbons and altered macromolecules of beetles in Dominican amber to still reacting cellular components of cypress twigs in Baltic amber [17, 18].

Compared to the large amounts of arthropods reported as inclusions in amber, only a small number of vertebrate remains of frogs, lizards, birds, mammals, and dinosaurs has been reported from different amber deposits from the Cretaceous to the Neogene around up to 120 million years old [19–27]. Most of these findings refer to small arboreal lizards of the family Gekkonidae and the genus Anolis, comprising partial remains to complete specimens [28–38]. X-ray scans revealed that parts of the skeleton are preserved in most of these specimens [28, 39, 40], but despite this observation, nothing is known about the degree of preservation of bone material in amber. One obvious hypothesis is that bones that were embedded in amber and thus shielded against aqueous solutions, may show a high degree of preservation, including their collagen matrix.

To address this question, we examine the left forelimb of an Anolis sp. indet. in a piece of 15 to 20 Million years old Dominican amber, also including a fairy wasp (Mymaridae, Fig 1A and S1 Fig), by micro-Raman spectroscopy, electron microprobe, and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). A detailed description of the fossil specimen is provided in the Supporting Information (S1 Appendix, S1–S3 Figs).


*Read original study online at http://fluoridealert.org/wp-content/uploads/barthel-2020.pdf


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*Read original study online at http://fluoridealert.org/wp-content/uploads/barthel-2020.pdf