Oxygen Isotopes in Carbonate and Phosphate of Modern Mammal Bioapatite: New Data and Critical Revision after about 25 Years from the First Recognitions

Oxygen and carbon isotopes of well-preserved skeletal remains give relevant support to archaeological and environmental reconstructions. However, the preservation of the skeletal remains must be preliminarily checked. About twenty-five years ago, a diagnostic method based on the oxygen isotope ratio in the phosphate, $\mathsf{\delta }{(\mathrm{O}_{}^{18}/\mathrm{O}_{}^{16})}_{\mathrm{Ph}},$ and carbonate, $\mathsf{\delta }{(\mathrm{O}_{}^{18}/\mathrm{O}_{}^{16})}_{\mathrm{Carb}},$ of bioapatite of modern mammals was proposed: for well-preserved samples, the $\mathsf{\delta }{(\mathrm{O}_{}^{18}/\mathrm{O}_{}^{16})}_{\mathrm{Ph}}$ and $\mathsf{\delta }{(\mathrm{O}_{}^{18}/\mathrm{O}_{}^{16})}_{\mathrm{Carb}}$should plot near the regression line $\mathsf{\delta }{(\mathrm{O}_{}^{18}/\mathrm{O}_{}^{16})}_{\mathrm{Ph}}$ on $\mathsf{\delta }{(\mathrm{O}_{}^{18}/\mathrm{O}_{}^{16})}_{\mathrm{Carb}}$ obtained for modern mammals. In the last twenty years, techniques of analysis have changed. In the past, ${\mathrm{BiPO}}_4$or ${\mathrm{Ag}}_3{\mathrm{PO}}_4$were precipitated from dissolved bioapatite and analysed with the fluorination technique, whereas at present, temperature reduction (HTR) in a glassy carbon reactor with $\mathrm{CO}$release is commonly used. Taking into account the HTR technique, for some modern mammals, we report a new$\mathsf{\delta }{(\mathrm{O}_{}^{18}/\mathrm{O}_{}^{16})}_{\mathrm{Ph}}$ + 1 on $\mathsf{\delta }{(\mathrm{O}_{}^{18}/\mathrm{O}_{}^{16})}_{\mathrm{Carb}}$ + 1 regression line, and related dispersion of the data that, in addition to mineralogical and structural methods, may be used to select samples reliable for archaeological use. In the past, other similar regression lines on modern mammals were defined by several authors. However, statistical results indicate that data used for these regression lines cannot be pooled because the hypothesis of a similar elevation is rejected.