When compared to a database of modern foliar physiognomy and climate, the physiognomy of a new collection of dicotyledonous leaves from the 10.66 +/- 0.06 Ma Jakokkota flora, Bolivian Altiplano, implies a mean annual temperature (MAT) of 18.6-21.0 +/- 2.5 degrees C. Similarly, a literature-derived sample of the early-middle Miocene Potosi flora, Cordillera Oriental, implies a MAT of 21.5-21.7 +/- 2.1 degrees C. We estimate that both floras experienced a growing season precipitation of 50 +/- 40 cm. The paleoclimate thus appears considerably warmer than the current highland climate, with MATs of 8-9 degrees C; the paleoprecipitation is indistinguishable from modern levels. A comparison of the Miocene MATs with the modern MATs, with the effects of latitudinal continental drift and global climate change subtracted, suggests that the Jakokkota flora grew at an elevation of 590-1610 +/- 1000 m, and the Potosi flora grew at an elevation of 0-1320 +/- 1000 m. Both paleoelevation estimates are significantly lower than the present elevations of 3940 and 4300 m, respectively, requiring a substantial component of Andean uplift since 10.7 Ma. This uplift history is consistent with two-stage tectonic models of Andean orogeny. (C) 1998 Elsevier Science Ltd. All rights reserved.
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