Synchrotron imaging reveals bone healing and remodelling strategies in extinct and extant vertebrates

Abstract

Current understanding of bone healing and remodelling strategies in vertebrates has traditionally relied on morphological observations through the histological analysis of thin sections. However, chemical analysis may also be used in such interpretations, as different elements are known to be absorbed and used by bone for different physiological purposes such as growth and healing. These chemical signatures are beyond the detection limit of most laboratory-based analytical techniques (e.g. scanning electron microscopy). However, synchrotron rapid scanning–X-ray fluorescence (SRS–XRF) is an elemental mapping technique that uniquely combines high sensitivity (ppm), excellent sample resolution (20–100 µm) and the ability to scan large specimens (decimetre scale) approximately 3000 times faster than other mapping techniques. Here, we use SRS–XRF combined with microfocus elemental mapping (2–20 µm) to determine the distribution and concentration of trace elements within pathological and normal bone of both extant and extinct archosaurs (Cathartes aura and Allosaurus fragilis). Results reveal discrete chemical inventories within different bone tissue types and preservation modes. Chemical inventories also revealed detail of histological features not observable in thin section, including fine structures within the interface between pathological and normal bone as well as woven texture within pathological tissue.

Incremental distribution of strontium and zinc in great ape and fossil hominin cementum using synchrotron X-ray fluorescence mapping

“…Strontium levels in mineralised hard tissues are thought to mirror physiological levels in tissue fluid [22,25], which in turn reflects geographical and geological location [26,27] and dietary intake, especially since some plants, nuts and fruits (and seafood) concentrate Sr [47] and perhaps because dust from soil on vegetation and foodstuffs can vary between seasons. Strontium concentrations also depend upon the degree to which a cascade of metabolic processes discriminate against or favour Sr relative to Ca [25].…”

“…Nonetheless, the retention of Zn in fossil cementum and secondary dentine, raises hopes that Zn as a marker of cementum growth increments, might prove useful in future life history studies of early hominins especially from other fossil locations more favourable to trace element preservation [22]. Iron and calcite distribution on exposed surfaces and within cracks and fissures and even at higher resolution within the Sharpey's fibre spaces and cementocyte lacunae appear not to have penetrated the denser tissues (electronic supplementary material figures S7,S8).…”

“…Lieberman [15] suggested nutritional status determines the rate of acellular cementum formation but also that changes to the magnitude and frequency of chewing forces underlie shifts in the orientation of the principal collagen fibres within the PDL that in turn determine the angle at which Sharpey's fibres become embedded within forming cementum [21]. Some or many of these aspects of cementum microstructure may be preserved in fossil teeth, as they are in fossil bone [22], and so potentially provide information about the diet and lifespan of extinct taxa.…”

“…A number of studies have identified zinc in bone and dental tissues [19,22,[28][29][30][31][32][33][34][35]. Overall, cementum is zinc-enriched (407 ppm) compared with dentine and bone [34].…”

Informative Potential of Multiscale Observations in Archaeological Biominerals Down to Nanoscale

“…Nowadays, two and sometimes three-dimensional (2D and 3D) elemental, molecular, structural and isotopic imaging of entire objects has becomes possible owing to recent technological developments off ocused analytical probes used in scanning mode and detectors (e.g. Lebon et al 2011a;Reiche et al 2011aReiche et al , 2003Reiche et al , 2010Reiche and Chalmin 2008;Anne et al 2014;Bergmann et al 2010;Gueriau et al 2014;Gourrier et al 2007bGourrier et al , 2010.…”