Size and size distribution of apatite crystals in sauropod fossil bones

Two complementary techniques, X-ray diffraction and transmission electron microscopy, were used to analyze the size and size distribution of apatite crystallites in subfossil mammal and fossil sauropod dinosaur bones. The transmission electron microscope (TEM) samples were prepared by Focused Ion Beam (FIB). X-ray diffraction indicates that crystals in sauropod bones are larger than in subfossil mammal bones. For sauropods the average crystallite size (both in length and width) does not seem to increase with bone length. A similar result was obtained from TEM investigations regarding crystallites aspect ratio (length/width). The distribution of crystallite sizes in a juvenile sauropod was found to be much wider compared to an adult bone originating from the same bed and locality, consistent with the hypothesis that young animal bone contains a mixture of crystallite sizes, with a beneficial effect on mechanical properties. Diagenesis effects on crystal size dimensions have been considered.