A palaeobiogeographic model for biotic diversification within Amazonia over the past three million years

Many hypotheses have been proposed to explain high species diversity in Amazonia, but few generalizations have emerged. In part, this has arisen from the scarcity of rigorous tests for mechanisms promoting speciation, and from major uncertainties about palaeogeographic events and their spatial and temporal associations with diversification. Here, we investigate the environmental history of Amazonia using a phylogenetic and biogeographic analysis of trumpeters (Aves: Psophia), which are represented by species in each of the vertebrate areas of endemism. Their relationships reveal an unforeseen 'complete' time-slice of Amazonian diversification over the past 3.0 Myr. We employ this temporally calibrated phylogeny to test competing palaeogeographic hypotheses. Our results are consistent with the establishment of the current Amazonian drainage system at approximately 3.0-2.0 Ma and predict the temporal pattern of major river formation over Plio-Pleistocene times. We propose a palaeobiogeographic model for the last 3.0 Myr of Amazonian history that has implications for understanding patterns of endemism, the temporal history of Amazonian diversification and mechanisms promoting speciation. The history of Psophia, in combination with new geological evidence, provides the strongest direct evidence supporting a role for river dynamics in Amazonian diversification, and the absence of such a role for glacial climate cycles and refugia.

NEW FOSSIL RECORDS OF PLEISTOCENE MARINE MOLLUSKS IN SOUTHERN BRAZIL

Fossils of the gastropods Diodora patagonica, Zidona dufresnei, Olivancillaria carcellesi, Lamniconus lemniscatus carcellesi and the bivalve Arcinella brasiliana are registered for the first time from the outcrops of Chui Creek, on the coastal plain of Rio Grande do Sul State, southernmost Brazil, together with other taxa previously known elsewhere. The specimens were collected in a shallow Pleistocene marine facies exposed at the base of the banks of the creek, in a fossil concentration possibly formed by storm events. The taxa described here live in shallow environments (with the exception of A. brasiliana and Z. dufresnei) with sandy bottoms (except for D. patagonica, T patagonica, B. odites, C. rhizophorae and A. brasiliana). The presence of L. lemniscatus carcellesi, found living today only in Uruguay and Argentina, indicates a wider distribution for this taxon during the late Pleistocene.

Rock Art at the Pleistocene/Holocene Boundary in Eastern South America

Background: Most investigations regarding the First Americans have primarily focused on four themes: when the New World was settled by humans; where they came from; how many migrations or colonization pulses from elsewhere were involved in the process; and what kinds of subsistence patterns and material culture they developed during the first millennia of colonization. Little is known, however, about the symbolic world of the first humans who settled the New World, because artistic manifestations either as rock-art, ornaments, and portable art objects dated to the Pleistocene/Holocene transition are exceedingly rare in the Americas. Methodology/Principal Findings: Here we report a pecked anthropomorphic figure engraved in the bedrock of Lapa do Santo, an archaeological site located in Central Brazil. The horizontal projection of the radiocarbon ages obtained at the north profile suggests a minimum age of 9,370640 BP, (cal BP 10,700 to 10,500) for the petroglyph that is further supported by optically stimulated luminescence (OSL) dates from sediment in the same stratigraphic unit, located between two ages from 11.7 +/- 0.8 ka BP to 9.9 +/- 0.7 ka BP. Conclusions: These data allow us to suggest that the anthropomorphic figure is the oldest reliably dated figurative petroglyph ever found in the New World, indicating that cultural variability during the Pleistocene/Holocene boundary in South America was not restricted to stone tools and subsistence, but also encompassed the symbolic dimension.

Upper Pleistocene to Holocene peatland evolution in Southern Brazilian highlands as depicted by radar stratigraphy, sedimentology and palynology

Paleoenvironmental interpretation of proxy data derived from peatlands is largely based upon an evolutionary model for ombrotrophic bogs, in which peat accumulates in still environments. Reports on proxies obtained from minerotrophic fens, where hydrologic inputs are variable, are less common. In this study, a highland peatland in southern Brazil is presented through ground penetrating radar (GPR) and sedimentological, palynological and geochronologic data. The radar stratigraphic interpretation suggests a relatively complex history of erosion and deposition at the site since the beginning of Marine Isotope Stage 3 (MIS 3) interstadial period. In spite of this, radar stratigraphic and palynologic interpretations converge. Electromagnetic reflections tend to group in clusters that show lateral coherence and correlate with different sediment types, while pollen grains abound and are well preserved. As a result, the study of minerotrophic fens provides a source of proxies. suggesting that ombrotrophic bogs are not the only reliable source of data in wetlands for palynological analysis. (C) 2012 University of Washington. Published by Elsevier Inc. All rights reserved.