Disparities in correlating microstructural to nanostructural preservation of dinosaur femoral bones

Abstract

Osteohistological researches on dinosaurs are well documented, but descriptions of direct correlations between the bone microstructure and corresponding nanostructure are currently lacking. By applying correlative microscopy, we aimed to verify that well-preserved osteohistological features correlate with pristine fossil bone nanostructures from the femoral bones of Koreanosaurus boseongensis. The quality of nanostructural preservation was evaluated based on the preferred orientation level of apatite crystals obtained from selected area electron diffraction (SAED) patterns and by measuring the “arcs” from the {100} and {002} diffraction rings. Unlike our expectations, our results revealed that well-preserved microstructures do not guarantee pristine nanostructures and vice versa. Structural preservation of bone from macro- to nanoscale primarily depends on original bioapatite density, and subsequent taphonomical factors such as effects from burial, pressure, influx of external elements and the rate of diagenetic alteration of apatite crystals. Our findings suggest that the efficient application of SAED analysis opens the opportunity for comprehensive nanostructural investigations of bone.

Correlative microscopy of the constituents of a dinosaur rib fossil and hosting mudstone: Implications on diagenesis and fossil preservation

“…We mainly focused on identifying the clay phases and investigating their microstructures and chemistry. We also investigated the arrangement of the apatite phases within the rib bone matrix by SAED pattern analysis [ 18 ].…”

“…Fig 8 shows the specific sampled regions. We evaluated the degrees of preferred orientation mainly based on the length and intensity of “arc” rings of the {100} and {002} planes [ 18 ], which are in a perpendicular arrangement. The overlapping {211}, {112}, {300} rings have the highest intensity [ 33 ] and this feature was the main criteria for verifying that the SAED patterns were taken directly from apatite crystals.…”

“…Chemical analysis on a microscopic scale of fossil bone allows further evaluation of elements that have native and/or external origins [ 7 – 12 ]. Although the general nanostructure of fossilized bone can be investigated through novel X-ray techniques [ 13 ], transmission electron microscopy (TEM) analysis directly provides information on the morphology, arrangement, and chemistry of fossil apatite nanocrystals [ 9 , 14 – 18 ]. Such data are crucial for understanding how these apatitic crystalline phases have originated and also how the bone structure was maintained during fossilization.…”

“…We also considered it as an ideal research material without inflicting considerable damage to the holotype specimen. Due to the small size and fractured state of the rib bones, correlating microstructural and nanostructural preservation of osteohistological features were mainly performed on the larger and more intact femoral bones from the paratype specimens [ 4 , 18 ].…”

Development of SEM and STEM-in-SEM grid holders for EDS analysis and their applications to apatite phases

“…Both synthetic and natural apatite samples (Kim et al, 2018;Song et al, 2012;Meneghini et al, 2003;Young et al, 1969;Kim et al, 2017) were used to test the efficacy of the modified holder for STEM-in-SEM EDS analysis. While commercial SAp was available in powder form, mineral apatite (MAp, 470104-508, Ward's Science) and fossil apatite (FAp, left femur from a Cretaceous dinosaur (Kim et al, 2017)) required powdering via diamond sawing (debris collection), ultrasonic drilling, and/or were ground with an agate mortar and pestle in order to avoid chemical and structural alterations. In case of bone apatite (BAp), aiming to retain its original state, we avoided using chemical agents that were involved in decalcification and fixation (Kim et al, 2018).…”