The samples were prepared for apatite δ13C and δ18O analysis from 58 distinct locations taken along the growth axes of the tooth (see Fig. 2), from the occlusal surface to the base of the sloth tooth. Preparation procedures followed those outlined by Balasse and colleagues (13). Using a 0.9-mm diamond burr microdrill tip, at each of the 58 locations, 5 to 15 mg of sample were removed from the tooth and collected in a microcentrifuge tube. During drilling, all cracks in the surface of the tooth were avoided to prevent contamination. To remove organics, 1.5 ml of 2.6% NaOCl was added to each sample and left uncapped overnight. After 24 hours, the NaOCL was rinsed from the sample with three washes in distilled water. Next, 0.1 M acetic acid was added to remove secondary carbonates. All samples were left for precisely 4 hours before they were rinsed clean with three washes of distilled water. The samples were then placed in the freezer for 45 min at the ISGS Stable Isotope Laboratory. Samples weighing 550 to 700 μg were placed in glass tube reaction vessels for phosphoric acid reactions. Samples were run on the Finnigan MAT 252 Isotope Ratio Mass Spectrometer with an attached KIEL III carbonate device. The precision values are 0.1 and 0.2‰ for δ13C and δ 18O, respectively. All results (table S2) are reported using d notation, δ = [(Rsample/Rstandard − 1) × 1000], where oxygen isotope values R = 18O/16O and all values are reported against V-SMOW (40). For carbon isotope values, R = 13C/12C and all values are reported against V-PDB (41).

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