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Biomineralized tissues are chemically altered after death, and this diagenetic alteration can obscure original biological chemical features or provide new chemical information about the depositional environment. To use the chemistry of fossil biominerals to reconstruct biological, environmental or taphonomic information, a solid appreciation of biomineralization, mineral diagenesis and biomineral-water interaction is needed. Here, I summarize the key recent developments in the fields of biomineralization and post-mortem trace element exchange that have significant implications for our understanding of the diagenetic behaviour of biominerals and the ways in which biomineral chemistry can be used in palaeontological and taphonomic research. [ABSTRACT FROM AUTHOR]

Abstract: The distribution of rare earth elements (REEs) within fossil bones is controlled by their partition coefficients between apatite and pore waters, and the rate of diffusion through the bone. Using simple theoretical models, we show that REEs are strongly fractionated from one another during diffusive transport and adsorption. Fractionation occurs due to the relative ease of substituting REE ions of differing ionic radius into the Ca sites in the apatite lattice, and the degree of fractionation is dependent on the rate of diffusion of ions within bone (and therefore the rate of recrystallisation). Variations in bone thickness, recrystallisation rate, and potentially pore water composition may all influence the relative distribution of REEs, and thus REE ratios within bones. Increases in bone thickness and reductions in either diffusion coefficients or the duration of REE uptake lead to enhanced fractionation of REEs in our model simulations. Interpretations of REE ratios in fossil bones either for palaeoenvironmental or taphonomic applications must consider how fractionation will influence REE ratios within bones, particularly when interpreting spatially resolved analyses within single bones. [Copyright &y& Elsevier]

Abstract: Spectroscopic indicators of bone crystallinity such as the infrared splitting factor (IRSF) are commonly used to determine the general state of preservation of ancient bone. In principle such indices might be expected to act as a proxy for alteration of bone mineral and thus could be used to screen bones (or portions of bones) for likely preservation of in vivo biogenic trace element and stable isotope signals. We tested the relationship between IRSF and bone mineral composition in two suites of well-characterised recent and Pleistocene bones. Initially, crystallinity change and trace element uptake are correlated, apparently both controlled by decomposition of the organic phase and exposure of bone crystal surfaces. This relationship breaks down in older bones where authigenic phosphate growth and mineral–pore water interactions are no longer rate-limited by the breakdown of collagen and exposure of crystal surfaces. In these conditions the extent of chemical alteration of bone will be controlled by site specific conditions, and thus while FTIR spectra of bone provide a broad indication of organic content and apatite recrystallisation, they are not reliable proxies for the degree of diagenetic alteration in terms of biogenic geochemical signals. [Copyright &y& Elsevier]

Abstract: Preservation of intact macromolecules and geochemical signals in fossil bones is mainly controlled by the extent of post-mortem interaction between bones and sediment pore waters. Trace elements such as lanthanum are added to bone post-mortem from pore waters, and where uptake occurs via a simple process of diffusion and adsorption, the elemental distribution can be used to assess the relative extent of bone-pore water interaction and rate of recrystallisation. Distribution profiles can be parameterised effectively using simple exponential equations, and the extent of bone–water interaction compared within and between sites. In this study, the distribution of lanthanum within bone was determined by laser ablation ICP–MS in 60 archaeological and fossil bones from Pleistocene and Cretaceous sites. The rates of recrystallisation and potential for preservation of intact biogeochemical signals vary significantly within and between sites. Elemental profiles within fossil bones hold promise as a screening technique to prospect for intact biomolecules and as a taphonomic tool. [Copyright &y& Elsevier]

Bones exposed on tropical savannah grasslands of Amboseli National Park, Kenya undergo extensive post-mortem alteration within 40 years. A combined analytical approach involving TEM microscopy, trace metal analysis, FTIR spectroscopy, and petrographic analysis has revealed a complex, dynamic diagenetic environment operating within exposed bones, driven by evaporative transport of soil water from the bone/soil interface to the upper exposed surface of the bone. This process results in extensive bone/soil-water interaction, and is responsible for increases in the concentrations of trace elements such as Ba and La of 100 – >1000% within 15 years. The maximum and mean size of bone crystallites increases with continued exposure. This change in mean crystallite length is correlated positively with increases in bone crystallinity, which in turn is associated with degradation of the bone protein. Microbial decomposition is rarely observed in the Amboseli bones, but where present resulted in severe dissolution–reprecipitation of bone mineral. Many bones showed extensive permineralization of the larger vascular spaces with calcite and barite and, to a lesser extent, crandallite. Permineralization of unburied bones may account for 95% reduction in macro (micron–millimeter scale) porosity in the bone within 2 years of death.We produce a model for pre-burial diagenesis of bone in arid tropical environments that highlights extensive alteration of bone chemistry within 1–40 years post-mortem. [Copyright &y& Elsevier]

Elemental maps generated by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) provide a previously unavailable high-resolution visualization of the complex physicochemical conditions operating within individual bones during the early stages of diagenesis and fossilization. A selection of LA-ICP-MS maps of bones collected from the Late Cretaceous of Montana (United States) and Madagascar graphically illustrate diverse paths to recrystallization, and reveal unique insights into geochemical aspects of taphonomic history. Some bones show distinct gradients in concentrations of rare earth elements and uranium, with highest concentrations at external bone margins. Others exhibit more intricate patterns of trace element uptake related to bone histology and its control on the flow paths of pore waters. Patterns of element uptake as revealed by LA-ICP-MS maps can be used to guide sampling strategies, and call into question previous studies that hinge upon localized bulk samples of fossilized bone tissue. LA-ICP-MS maps also allow for comparison of recrystallization rates among fossil bones, and afford a novel approach to identifying bones or regions of bones potentially suitable for extracting intact biogeochemical signals. [ABSTRACT FROM AUTHOR]

Abstract: The diverse vertebrate remains from the Upper Cretaceous freshwater settings at Iharkút, Hungary, contain two fossil groups, Pycnodontiformes fish and Mosasauridae that are almost exclusively known from marine palaeo-environments. Hence, their appearance in alluvial sediments is very unusual. Trace element and isotope compositions of the remains have been analyzed to investigate the taphonomy and the ecological differences among the different fossil groups present at Iharkút. All examined fossils have undergone post-depositional diagenetic alteration, which resulted in high concentrations of REE, U, and Fe, together with almost complete homogenization of δ 18OCO3 values. Similar REE patterns in different fossils suggest a common origin for all remains, hence the discovered species most likely lived in the same local ecosystem. Despite partial diagenetic overprinting, the δ 18OPO4 values of the fossils indicate sufficient taxon-specific isotopic diversity to permit some broad conclusions on the palaeo-environment of the fossils. In particular, it is apparent that the isotopic composition of the Pycnodontiformes fish and Mosasauridae remains is most compatible with a freshwater palaeo-habitat and incompatible with a marine palaeo-environment. In addition, the Sr concentration and isotope data indicate that the Pycnodontiformes and Mosasauridae likely lived predominantly in a freshwater environment and were not simply occasional visitors to the Iharkút river ecosystem. Regarding other fossil groups, high δ 18OPO4 values of Alligatoroidea and Iharkutosuchus teeth suggest that these small crocodile species might have inhabited swamps and ponds where the water was relatively rich in 18O due to evaporation. [Copyright &y& Elsevier]