干旱区生态环境知识资源中心

The stable carbon isotope ratios of tooth enamel from 89 herbivores from the Dove Spring Formation (DSF) of the El Paso Basin, western Mojave Desert, California, were analyzed to determine if C-4 plants may have been present in the late Miocene of southern California. Taxa analyzed include antilocaprids, castorids, camelids, equids, gomphotheriids, merycoidodontids, and rhinocerotids. The atmospheric CO2-delta C-13 value has varied significantly in the geologic past, leading to changes in the delta C-13 values of plants and tooth enamel. The estimated delta C-13 value of atmospheric CO2 in the middle to late Miocene is -5.8 +/- 0.2 parts per thousand, making the pure C-3 diet cutoff value higher than the modern by similar to 2 parts per thousand. Given this, much of the evidence of an early spread of C-4, which inappropriately uses the modern C-3 diet cutoff value, may be a false signal from water-stressed C-3 plants and the amount of C-4 biomass in the geologic past may have been over-estimated. The enamel-delta C-13 values of all taxa sampled are -10.1 +/- 1.1 parts per thousand. (n = 89). Accounting for the changes in the delta C-13 values of atmospheric CO2, enamel-delta C-13 values from the DSF indicate that herbivores from that area had C-3 diets and lived in an environment dominated by C-3 plants. Serial enamel isotope data from the DSF revealed negligible intra-tooth variations in the delta C-13 values, confirming that these herbivores consumed C-3 plants year-round. If the C-4 photosynthetic pathway did spread to southern California prior to the rapid, global rise in C-4 in the late Miocene, the taxa sampled did not incorporate C-4 biomass into their diets. The results of the stable carbon isotope analysis, along with the evidence from the rock record and the life habits of the fossil taxa present, indicate that the El Paso Basin consisted of diverse habitats including C-3 grasslands, wooded C-3 grasslands, and riparian forests. (C) 2017 Elsevier B.V. All rights reserved.