Quantitative Evaluation

To quantify the crystal aspect variability, we conducted detailed imaging and statistical analyses on high resolution scanning electron micrographs of the four crystal morphologies described above. For each crystal type, the dimensions of length and width were measured. The raw results are presented in Fig. 12A. The figure also shows the length and width of granule aggregates (red color). A total of 1,075 randomly chosen crystals (specifically 350 perpendicularly oriented prismatic apatite crystals; 200 tangentially oriented bladed apatite crystals; 125 randomly oriented equant apatite crystals; 325 phosphatic granule aggregates; and 75 granules) were measured on scanning electron micrographs using Adobe Photoshop CS2. The data were analyzed using SAS 9.1 and plotted using DeltaGraph 5.0. Figure 12A illustrates the length-width plots of all four different types of crystal morphology. Figures 12B-C shows less obscured view of the four crystal morphologies - including measurements of granule aggregates.

To estimate the confidence intervals, the data were subject to a naive bootstrapping analysis (Efron, 1981; Kowalewski et al., 1998), with 1,000 iterations (SAS code written by M. Kowalewski and modified by R. Krause). Means and corresponding 95% confidence intervals of the lengths, widths, and aspect ratios for each of the above-described crystal morphologies are presented in Figs. 12D-E. The quantitative analysis shows that perpendicularly oriented, prismatic crystals are significantly larger than tangentially oriented, bladed crystals (Fig. 12D), although they have similar length:width ratios (Fig. 12E). The randomly oriented equant crystals and phosphatic granules are even smaller, and as expected have smaller aspect ratios. Thus, these four crystal morphologies are distinct in both shape and size. And the distinction of these crystal morphologies may aid in understanding factors affecting nucleation and growth of crystals in varying regions of multiple fossil taxa during the phosphatization process.

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