The Expansion of C4 Grasses in the Americas

古土壤碳酸盐的稳定碳同位素表明，C4热带 草迅速扩展到印度-恒河的洪泛平原， 平始约7.3 Ma。 大约在同一时间，C4草 开始在东非扩张。 碳同位素证据来自 来自美国中西部的牙齿化石表明最晚的中新世（8 ~ 6 Ma），C_4禾本科植物的出现时间。 我们 这里的目的是对C4草的辐射进行日期和量化 通过对古土壤和化石的详细取样， 来自美国新墨西哥州、拉里奥哈和圣的部分牙齿 阿根廷西北部的胡安省。 如果C4膨胀与 亚洲季风的开始或加强，就像以前一样， 建议，那么我们就不会期望在美洲扩张， 旧世界是同步的。 如果膨胀是同步的， 然后是涉及全球变化的其他解释，例如 减少大气pCO 2或其他原因，必须援引。

Stable carbon isotopes in paleosol carbonate show that C4 tropical grasses expanded rapidly onto the floodplains of the Indo-Gangetic Plain starting about 7.3 Ma. At about the same time, C4 grasses began their expansion in East Africa. Carbon isotope evidence from fossil teeth from the midwestern U.S. suggests a latest Miocene (8 to 6 Ma) date for the appearance of C4 grasses there as well. Our intent here is to date and quantify the radiation of C4 grasses across the Americas by detailed sampling of paleosols and fossil teeth from sections in New Mexico, USA, and in La Rioja and San Juan Provinces in NW Argentina. If the C4 expansion is related to onset or strengthening of the Asian Monsoon, as has been previously suggested, then we would not expect expansion in the Americas and the Old World to be synchronous. If the expansion is synchronous, then some other explanation involving a global change, such as reduction in atmospheric pCO2 or other causes, must be invoked.