Table 1.

Mean ± SD (n = 4–5 measurements in each sample) of macroelement composition (weight%) determined in the internal enamel by SEM-EDS. The first two rows are Crocodylia samples (Purussaurus sp., and M. niger), and the last two are Rodentia samples (Neoepiblema sp. and H. hydrochaeris). The Ca/P ratio corresponds to the expected for hydroxyapatite composition. Ca: calcium, P: phosphorus, Ca/P: ratio of calcium per phosphorus.

Sample	Ca (wt%)	P (wt%)	Ratio Ca/P
Fossil alligator	36.8 ± 24.4	16.5 ± 0.2	2.2 ± 0.03
Extant alligator	33.3 ± 0.4	16.6 ± 0.1	2.0 ± 0.03
Fossil rodent	38.6 ± 0.3	17.8 ± 0.1	2.2 ± 0.02
Extant rodent	36.8 ± 1.5	17.7 ± 1.3	2.1 ± 0.12