image: Part of an extinct giant sloth's upper humerus recovered by divers during the 2014 excavations. view more
Credit: Lisa J. Lucero, courtesy of VOPA
By analyzing a tooth from the first remains of an extinct giant ground sloth found in Belize, researchers have uncovered insights into the animal's dietary adaptations, as informed by local climate. In fossilized animals like it lacking tooth enamel, the authors discovered, tooth layers are affected differently by long sedimentary processes; thus, they say, if isotopic analyses are conducted on any other tooth layer than the inner orthodentin, conclusions will likely be inaccurate. While exploring a water-filled sinkhole in central Belize, divers discovered the fossilized remains of an extinct giant ground sloth (Eremotherium laurillardi). Since sloth teeth grow throughout an individual's life, studying the changes in stable isotope patterns along the length of the tooth could shed light on its diet and climatic exposure. With this in mind, Jean T. Larmon and colleagues examined carbon (δ13C) and oxygen (δ18O) stable isotope data from 58 samples derived from a single E. laurillardi tooth, which they supplemented with cathodoluminescence analysis to assess the reliability of the data. These samples were taken from three apatite layers of the tooth - the cementum, and also the outer and inner layers of the orthodentin. The authors found a noticeable variation in the δ13C results when comparing the layers, which suggests these layers are affected differently by chemical and physical processes as they fossilize. In this case, the authors found the inner layer of the orthodentin to be most resistant, and therefore likely to return the most accurate results. Knowing this, Larmon et al. used a "vacuum milling" technique in a weak acid to date this inner orthodentin layer, and they concluded the age of the tooth was around 27,000 years before present - a time when Earth was cold, during the Last Glacial Maximum. What is more, fluctuations in δ18O ratios along the tooth show a distinct pattern of two short wet seasons divided by a longer dry season, indicating that the sloth lived through annual periods of aridity. Larmon et al. say that the higher δ13C values when δ18O values are the lowest may mean that grasses and shrubs likely comprised a large amount of the sloth's diet during the wet season. The data suggests that the animal's diet varied seasonally, that giant ground sloths in Belize were likely opportunistic feeders. Their diverse diet would have increased their habitat and distribution, the authors say.
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Journal
Science Advances