PRF/M: Age of the Amazon Rainforest: New Evidence Using Stable Isotopes and Fossil Mammals

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Stable isotopes such as carbon-13 can be used to analyze diets of mammals that inhabited the Amazon River basin during the late Quaternary period, as well as local habitats and regional climates. Prior studies of fossil mammals and paleosol carbonates indicate the Amazon has undergone major change within the last few to several tens of thousands of years. This assertion can be tested by assessing the types of plants eaten by herbivores of ancient ecological communities because: (a) incorporation into animal hard tissues (bone, dentine, enamel) of photosynthetic carbon is from only two sources - - C3 (Calvin cycle) plants or C4 (Hatch-Slack cycle) plants, and the ratio of each type plant gives a clue as to the composition of the prevalent vegetation at the time; (b) isotopic content of carbon from carbon dioxide can be measured by mass spectroscopy using pulverized fossil or carbonate samples. Analysis of carbonates precipitated in ancient soils and fossilized bone, some of which was originally hydroxyapatite ıCa10- (PO4)6-(OH)2!, highly porous and subject to diagenesis (secondary alteration of the original chemical composition). More than 25 species of mammals from several Orders should be available, including Edentata (e.g., mylodont sloths, Megalonyx, armadillos, glyptodonts), Proboscidea such as Haplomastodon, Perissodactyla (Tapirus), Artiodactyla, and Notoungulata. %%% Results should yield insight into the question of whether the present Amazon rainforests were formerly covered at least to some extent by grasslands. These findings may in turn reveal to what extent global changes have been directional or cyclic over extended time periods.