-Our study provides paleontological and geological data substantiating a paleoenvironmental model for the upper Miocene-Pliocene of Southwestern Amazonia. The extensive Late Tertiary sediments of The Solimões Formation, outcropping in Southwestern Amazonia, were deposited by a complex megafan system, originating in the high Peruvian Andes. The megafan system was the sedimentological response to the Andean Quechua tectonic phase of Tertiary age, producing sediments that fdled the foreland basin of Southwestern Amazonia. Occurrences of varied vertebrate fossil assemblages of the HuayquerianMontehermosan Mammal age collected in these sediments support this interpretation. The fauna includes several genera and species of fishes, reptiles, birds, mammals and appears to be one that could have lived in or near a riverine habitat. In the Late Pliocene, the megafan system became inactive as a result of the influence of the Diaguita Tectonical Phase.

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-A new species of turtle, Stupendemys souzai, is based on one incomplete humerus and additional material from several outcrops of the Solimões Formation in the state of Acre. Diagnostic features of the species include the humerus noticeably less massive than in Stupendemys geographicus, the thick curved margin of the nuchal and peripheral 1 plates, the femoroanal sulcus located very anteriorly on the xiphiplastral plate, the posterior lobe of the plastron short and broad and the centrum of cervical vertebrae relatively narrow and excavated laterally.