Renato Pereira Lopes

Biostratigraphy of the Pleistocene Fossiliferous Deposits of the Southern Brazilian Coastal Area

Fossils of Pleistocene mammals have been discovered in the southern Brazilian coastal area since the late XIX century, in two main places: the continental shelf and the Chuí Creek. Although the taxonomic composition of fossil assemblages from these areas has been the focus of most studies during the late XX century, research concerning the ages, stratigraphic position, and biostratigraphy of such assemblages remains scarce. This is due to the lack of suitable materials for age determination and the reworked nature of the fossiliferous deposits in the continental shelf. Only in recent years have new data shed light on these subjects. Taxonomic revisions, ESR ages, and biostratigraphic correlations confirm a late Pleistocene age for the fossil assemblages, although those from the shelf represent a significant time averaging, while fossils from the Chuí Creek exhibit a narrower age range. The fossil mammals found in southern Brazil represent a mixture of Brazilian and Pampean taxa, including forms that disappeared much earlier from the Argentinean pampas. Gaining an understanding of the biostratigraphic context of such assemblages in comparison to similar assemblages from Argentina and Uruguay, in conjunction with stratigraphic, geomorphological, and paleoclimatic data should provide additional tools with which to reconstruct the environmental and climatic dynamics of this portion of South America during the late Pleistocene—early Holocene and its effects on the fauna, and possibly to help address the problem of the disappearance of megamammals in the area.

The sea-level highstand correlated to marine isotope stage (MIS) 7 in the coastal plain of the state of Rio Grande do Sul, Brazil.

The coastal plain of the state of Rio Grande do Sul, in southern Brazil, includes four barrier-lagoon depositional systems formed by successive Quaternary sea-level highstands that were correlated to marine isotope stages (MIS) 11, 9, 5 and 1, despite the scarcity of absolute ages. This study describes a sea-level highstand older than MIS 5, based on the stratigraphy, ages and fossils of the shallow marine facies found in coastal barrier (Barrier II). This facies outcrops along the banks of Chuí Creek, it is composed of fine, well-sorted quartz sand and contains ichnofossils Ophiomorpha nodosa and Rosselia sp., and molluscan shells. The sedimentary record indicates coastal aggradation followed by sea-level fall and progradation of the coastline. Thermoluminescence (TL) and electron spin resonance (ESR) ages from sediments and fossil shells point to an age of ∼220 ka for the end of this marine transgression, thus correlating it to MIS 7 (substage 7e). Altimetric data point to a maximum amplitude of about 10 meters above present-day mean sea-level, but tectonic processes may be involved. Paleoceanographic conditions at the time of the highstand and correlations with other deposits in the Brazilian coasts are also discussed.

Discussões sobre a presença do gênero aeolosaurus powell 1987 (dinosauria, titanosauria) no cretáceo superior do Brasil

The records of Cretaceous Brazilian titanosaurs assigned to the Patagonian genus Aeolosaurus Powell (Dinosauria, Sauropoda, Titanosauria) are discussed. The fragmentary and isolated nature of many of the specimens and the incomplete knowledge of the diversity and phylogenetic relationships of Brazilian titanosaurs generate uncertainty regarding the taxonomic assignments. Revision of the Brazilian specimens attributed to Aeolosaurus suggests that there are no characters indicating the presence of this Patagonian genus in the Late Cretaceous of Brazil. The conclusion that the relationships of these specimens were incorrectly recognized, points out that better taxonomic procedures, using consistent data, such as the presence of well-defined apomorphies, are needed for correct taxonomic designations, paleogeographic and paleobiostratigraphic inferences and the proposal of biochrons. Key words: Titanosauria, Aeolosaurini, Aeolosaurus , Late Cretaceous, Bauru Group, Brazil.

Icnologia dos ostreídeos fósseis (bivalvia ostreoida) do sul da costa brasileira

Feicoes de bioerosao identificadas em ostreideos fosseis de acumulacoes da costa sul brasileira sao descritas. Os depositos sao caracterizados pela presenca dominante de Ostrea puelchana d’Orbigny, 1841, seguida por O. equestris Say, 1834 e Crassostrea virginica Gmelin, 1791. Embora esses taxons sejam encontrados ao longo de toda a costa, exibem variacoes geograficas com relacao a presenca de bioerosao. Os icnogeneros mais comuns sao Caulostrepsis e Entobia e Gastrochaenolites caracteriza a atividade mais comum entre aqueles do setor central da costa, sendo mais raro no setor sul. Maeandropolydora e incrustracoes (p. ex. cirripedios e briozoarios) sao pouco numerosas. A maioria das perfuracoes e encontrada na superficie externa das valvas, sugerindo que grande parte dos processos bioerosivos tenha ocorrido enquanto os organismos ainda estavam vivos. Palavras-chave: Quaternario, Ostreidae, bioerosao, Entobia , Caulostrepsis , Gastrochaenolites .

A New Method For Calculating The Accumulated Dose In Esr Dating And Retrospective Dosimetry

Dose evaluation by electron spin resonance (ESR) is usually accomplished by constructing a dose-response curve by measuring the peak-to-peak intensity of the dosimetric signals in the g = 2 region. In several cases, this signal is overlapped with others that can interfere with dose reconstruction. In this work a new method to correct the spectrum before the measurement of the signal intensity is proposed. Examples of dose determination of accumulated dose (AD) of two fossil teeth from southern Brazilian megafauna are given. One of them presents a dose-independent signal in the region of interest, and the validity of this method is shown. For the other, without interfering signals, no difference in the AD was found. This method can also be applied to retrospective dosimetry by ESR for any sample with dose-independent interfering signals, thus improving the accuracy in AD determination by ESR.

Fósseis de Scelidotheriinae Ameghino, 1904 (Xenarthra, Pilosa) em depósitos pleistocênicos do Rio Grande do Sul, Brasil

Xenarthra (Mylodontidae) is a mammal group which fossil record is conspicuous in Southern Brazil, and includes until now the Mylodontinae, Mylodon , Glossotherium and Lestodon and the Scelidotheriinae Catonyx . Here it is presented new fossils of Scelidotheriines, represented by a fragment of a dentary, plus other four isolated teeth. A detailed description of the only other record of scelidotheriinae in Rio Grande do Sul, consisting in an almost complete right dentary, is also presented. The lacking of additional and more complete fossils complicates a more precise taxonomic insertion. Nevertheless, the specimens exhibit features that allow their recognition as Catonyx . The fossils are tentatively assigned to C. cuvieri , based on the assumption that it is the only valid scelidotheriine recognized so far for southern Brazil. Key words: Xenarthra, Pilosa, Scelidotheriinae, Catonyx sp., Pleistocene, Brazil.