What the wild things ate; isotopic analysis of an extinct giant sloth tooth from Cara Blanca, Belize

Stable carbon and oxygen isotope ratios of a series of microsamples of bioapatite from the tooth of an extinct giant sloth (Eremotherium laurillardi) from central Belize were used to reconstruct seasonal variation in the sloth's diet and microclimate during tooth formation. This fossil was recovered from 60 m below the surface of a cenote (a water-filled karstic sinkhole). Cathodoluminescence (CL) microscopy was used to identify post-depositional chemical and mineralogical diagenesis accompanying fossilization. CL employs electron beam bombardment to stimulate visible light emission from the minerals comprising the fossilized tooth based on the major and minor element composition. Thus, CL analysis enables the user to identify diagenetic mineral recrystallization and replacement of the three major tissue types in sloth teeth: orthodentine, vasodentine and cementum. Results from CL analysis demonstrate that orthodentine, which is the least porous tissue type, is most resistant to alteration. Cracks in orthodentine cemented with diagenetic calcite crystals were avoided during sampling for radiocarbon dating and stable isotopic analyses. Twenty bioapatite microsamples (5-15 mg) were drilled from the orthodentine along 8.5 cm of the growth axis of the tooth. The results of isotopic analyses (delta (super 13) C: -9.1 to -10.9 ppm; delta (super 18) O: 26.9 to 29.1 ppm) establish a pattern of covariance that reflects moderate seasonal variation in stomatal conductance and evapotranspirative water stress of the C (sub 3) plants that this sloth consumed at the end of the last Ice Age. This giant ground sloth, standing 6m tall, likely climbed down the steep sides of the cenote for a drink during a particularly arid period, became trapped, died and was fossilized; its remains were recovered by divers thousands of years later.