Nondestructive recognition and differentiation of quasi-spherical structures of biologic interest

Background: Biological findings in archaeological and paleontological contexts are not limited to bones. In particular, biological concretions can present valuable infor- mation regarding the health of the organisms under examination. However, these structures are often difficult to recognize and identify. Chemical analyses (e.g., Raman spectroscopy) can allow their identification but they are time-consuming and destructive techniques, even if minimally so. In this research, the potential of nondestructive high magnification surface microscopy is investigated for the distinction of uroliths from other biological and nonbiological concretions, specifically gallstones, bezoars, gastric pellets, coprolites, eggs, gastroliths and geological concretions. Methods: The external surfaces of uroliths, bezoars, gastric pellets, gallstones, coprolites, gastroliths, eggs and geologic concretions were examined microscopically at 20, 50 and 200 magnification. Results: Morphological surface appearance of uroliths was independent of producer phylogeny and chemical composition and presented as smooth surfaces with level, faceted or lobulated configurations. Gallstones also presented a large array of shapes with smooth or porous external surfaces. Gastric pellets, bezoars and coprolites could be distinguished from other biological stones by the common presence of hair, sand grains, bone fragments or hair. Presence of uniform pores permitted the recognition of egg shells. Distinguishing gastroliths and geologic concretions requires additional diagnostic criteria. Conclusion: High magnification surface microscopy of biological concretions from reference collections permits a better understanding of biological concretions and their normal variation. In addition, it allowed the distinction of uroliths from most biological concretions. Nonetheless, gallstones constitute the major differential diag- nosis of uroliths, and destructive chemical analyses may be ultimately required for their distinction.