Renato Lopes

The Santa Vitória Formation is a lithostratigraphic unit known for its fossil assemblage of Pleistocene mammals, established in 1973 from sediments exposed along the banks of Chuí Creek, in the southern coastal plain of the state of Rio Grande do Sul (CPRS), Brazil. The original description was presented in a Masters' dissertation and never formally described in a peer-reviewed publication. Moreover, surveys and fossil collecting efforts developed in the last decade have led to a better understanding of its origin and nature. An updated description of this unit is presented here, which outcrops in areas occupied by barrier-lagoon depositional systems originated by eustatic oscillations. The formation encompasses Middle-Upper Pleistocene fluvial and eolian depositional systems and paleosols formed chiefly of fine to medium quartz sand, with subordinate clay, concentrations of iron and manganese oxides, and caliche nodules of pedogenic origin. It conformably overlies upper shoreface-foreshore marine deposits, and is overlain by loess deposited during the last glacial period. Here is proposed to redefine it as Santa Vitória Alloformation, considering that the use of an allostratigraphic framework to characterize this unit has the practical purpose of grouping depositional systems genetically unrelated to the barrier-lagoon systems.

Here are described the analyses of sediments from the lower slope of the Pelotas Basin in the southern Brazilian continental margin, southwestern Atlantic. The samples were obtained from the core SIS-249, collected adjacent to the Rio Grande Terrace (RGT) at a water depth of 2091 m, an area poorly known in terms of sedimentary characteristics compared to the oil and gas-rich basins to the north. The age model indicates that the sampled sediments were accumulated during the last glacial period, between 112.5 and 34.47 ka (MIS 5 to MIS 3). The fine (<63 μm) fraction is dominated by silt with subordinate clay, whereas the coarse (sandy) fraction is chiefly composed of biogenic carbonate (tests of foraminifers) with subordinate very fine (63-125 μm) lithogenic sand. The composition of the lithogenic sand is essentially uniform downcore, dominated by quartz with glaucony as the dominant accessory mineral, and the presence of augite, derived from Mesozoic volcanic rocks, points to a source from the adjacent coastal plain. The uniform mineral composition indicates continuous input of sediments removed from the RGT by action of the Brazil Current (BC) and transferred to the lower slope by gravity flows. The higher proportion of lithogenic sand from the upper RGT along the intervals corresponding to MIS 5 and MIS 3 points to erosion of the terrace due to a more landward position of the BC, related to sea-level highstand and falling stage tracts. The higher amount of silt along the MIS 4 interval suggests increased transfer of sediments from the flanks of the RGT as the result of a more downslope position of the BC driven by the sea-level lowstand. Winnowing of the sortable silt fraction during MIS 5 and 3 points to influence of the southward-flowing North Atlantic Deep Water (NADW). The higher estimated accumulation rates and less negative peaks of δ 13 C in benthic foraminifers Uvigerina peregrina during MIS 4 could have been caused by oscillations of water masses with distinct isotopic compositions, but also by increased burial and decomposition of organic matter as a result of high ocean surface primary productivity, indicated by the correspondence between the δ 13 C oscillations and higher accumulation rates and proportion of biogenic sand in the core. Higher productivity was apparently driven by episodes of increased eolian transport of dust from Patagonia and central-western Argentina in milenial timescales, coeval with oscillations in strength and position of the southern westerly winds (SWW) system.

The Late Pleistocene-early Holocene faunal turnover in South America was characterized by the
extinction of all mammals with body mass >300 kg and several smaller taxa, but the driving mechanisms
behind it are still poorly understood. Here is presented an analysis of the extinction in the Pampa of
southern Brazil (Rio Grande do Sul state), based on fossil assemblages found in the coastal plain (CPRS)
and western area of the state (WRS). The comparison between fossil and extant mastofaunas show that
90% of the mammals represented in fossil assemblages went extinct, and allowed distinguishing three
groups: 1) taxa that underwent local extinction, i.e., disappeared locally but survived in other regions
until becoming extinct later (including all megamammals); 2) pseudoextinct taxa that disappeared
locally but survive until today in other areas, and 3) taxa that disappeared locally but returned during the
Holocene. The faunal changes recorded along stratigraphic successions and available numerical ages
indicate two phases of extinction, the first around 30 ka b2k in the CPRS (apparently also recorded in
Argentina and Uruguay) would have been related to the onset of the cold and dry conditions of the
stadial MIS 2, predating the arrival of humans to the region by about 25 kyrs. The second phase eliminated
taxa that survived until about 12.7 ka BP in WRS in reduced suitable environments (‘refugia’)
associated with perennial rivers; it coincides with the transition from glacial to interglacial conditions,
but pollen data suggest that humans may have contributed for environmental modifications through fire.
The results show that the Pleistocene xenarthran-dominated mastofauna was replaced by a Holocene
fauna dominated by small rodents and carnivores, and indicate that climate-driven environmental
changes, also influenced by sea-level oscillations, were a major agent in the Late Pleistocene mammalian
extinctions in the Brazilian Pampa.

The presence of the extinct sloth Megatherium americanum Cuvier in Pleistocene deposits of the Coastal Plain of the State of Rio Grande do Sul, southern Brazil, has been mentioned by several authors for decades, but formal descriptions of skeletal elements with unambiguous diagnostic features have never been published. The recent description of one dentary of the megatheriid Eremotherium laurillardi Lund from deposits in this area raised doubts about the taxonomic affinity of the materials assigned to M. americanum. The present work confirms the presence of the latter in the coastal plain of the state of Rio Grande do Sul (Santa Vitória do Palmar County), from a partial skull collected in fluvial deposits of the Santa Vitória Formation exposed on the banks of the Chuí Creek, plus an incomplete dentary, one tibia, one astragalus found on the shoreline, and another tibia with the fibula fused proximally and distally retrieved from the bottom of the continental shelf by the research vessel "Atlântico Sul". The fossils of both species of megatheriid sloths were found in the same deposits of Rio Grande do Sul (Chuí Creek in the coastal plain and Pessegueiro Creek in the central area of the state), which is remarkable given that E. laurillardi is known mostly from the intertropical Americas, whereas M. americanum is restricted to the subtropical-temperate regions of South America. Such co-occurrence could indicate that both species were sympatric or be related to the mixing by fluvial processes of remains of animals that occupied the same areas at distinct times due to periodic latitudinal shifts of the climatic belts. RESUMO-A presença da preguiça-gigante extinta Megatherium americanum Cuvier em depósitos do Pleistoceno na região costeira do sul do Brasil tem sido citada por diversos autores por décadas, mas descrições formais de elementos esqueletais com caracteres diagnósticos não foram ainda apresentadas. A recente descrição de um dentário do megaterídeo Eremotherium laurillardi Lund em depósitos desta região levantou dúvidas sobre a afinidade taxonômica dos materiais atribuídos a Megatherium. Aqui é confirmada a presença deste na Planície Costeira do Estado do Rio Grande do Sul (Município de Santa Vitória do Palmar), a partir de um crânio parcial coletado em um depósito fluvial da Formação Santa Vitória exposto nas barrancas do Arroio Chuí, um dentário incompleto, uma tíbia e um astrágalo encontrados na linha de costa, e de uma tíbia com a fíbula fusionada proximal e distalmente coletadas na plataforma continental pelo navio de pesquisas "Atlântico Sul". Nos mesmos depósitos do Rio Grande do Sul (Arroio Chuí na planície costeira e Arroio Pessegueiro no centro do estado) foram encontrados fósseis de ambas as espécies de megaterídeos, o que é notável, considerando que E. laurillardi é característico da zona intertropical das Américas, enquanto M. americanum é um táxon restrito à região subtropical-temperada da América do Sul. Essa co-ocorrência poderia indicar que ambas as espécies eram simpátricas (i.e. coexistiram ocupando distintos nichos ecológicos), ou estar relacionada à mistura por processos fluviais de restos de animais que ocuparam as mesmas áreas em épocas distintas devido a mudanças latitudinais periódicas das zonas climáticas. Palavras-chave: Megatheriidae, Megatherium, Pleistoceno, paleobiogeografia, paleoambiente.

The avian fossil record of southern Brazil is scarce, consisting of few isolated remains. Here is described a ciconiid fossil from the assemblage of mammalian remains of the Santa Vitória Formation (SVF). The specimen is a cervical vertebra morphologically similar to Ciconia maguari (maguari stork), common in southern Brazil today. Nevertheless, its larger dimensions suggest that it could be either a morphotype of that species or another, extinct species. The taphonomic modifications of the vertebra result of a combination of autogenic and allogenic factors including the aquatic habit, shape and transportation by flowing water and burial in a shallow stream. The fossil-bearing sediment dated by luminescence was deposited during the late Pleistocene, at 37.9 ka b2k, and exhibits physical features indicating deposition under variable discharge and seasonal oscillations of the water table. The presence of an aquatic bird in these sediments indicates a period of increased precipitation, chronocorrelated to one of the millenial-scale warming pulses recorded in ice cores from Antarctica (Antarctic Isotope Maxima) that characterized the interstadial MIS 3. On the other hand, the dry and cold climate of the following glacial MIS 2 may have forced ciconiids and aquatic mammals to retreat to suitable areas (refugia), as indicated by their absence in the loess deposits (Cordão Formation) overlying the SVF, until returning during the Holocene when climate became wet and warm again. The results presented here increase the avian fossil record of southern Brazil and help understand the role of climate change on the distribution of ciconiid birds and other taxa during the Quaternary in southern South America.

RESUMO-O registro fóssil de aves do sul do Brasil é escasso e consiste de poucos elementos isolados. Aqui é descrito um fóssil de ciconídeo na assembleia de restos de mamíferos da Formação Santa Vitória. O espécime consiste de uma vértebra cervical morfologicamente similar a Ciconia maguari (joão-grande), comum atualmente no sul do Brasil. Entretanto, suas dimensões maiores sugerem que poderia ser um morfotipo daquela espécie ou outra espécie extinta. As modificações tafonômicas na vértebra resultam da combinação de fatores autogênicos e alogênicos incluindo o hábito aquático, forma e transporte por água corrente e soterramento em um riacho raso. O sedimento fossilífero datado por luminescência foi depositado no Neopleistoceno, há 37,9 ka, e exibe características que indicam deposição sob descarga variável e oscilações sazonais do lençol freático. A presença de uma ave aquática em sedimentos depositados por água indica um período de precipitação elevada, cronocorrelacionado a um dos pulsos quentes em escala milenial registrados em testemunhos de gelo da Antártica (Máximos Isotópicos Antárticos) que caracterizaram o interestadial MIS 3. Por outro lado, o clima frio e seco do glacial seguinte MIS 2 pode ter forçado os ciconídeos e mamíferos aquáticos a se retirarem para áreas adequadas (refúgios), como sugere sua ausência nos depósitos de loess (Formação Cordão) acima da FSV, até retornar durante o Holoceno, quando o clima se tornou úmido e quente novamente. Os resultados apresentados aqui ampliam o registro fóssil de aves do sul do Brasil e ajudam a compreender o papel das mudanças climáticas na distribuição de aves ciconídeas e outros táxons durante o Quaternário no sul da América do Sul. Palavras-chave: Ciconiidae, Formação Santa Vitória, tafonomia, MIS 3, paleoambiente, paleoclima.

Neste trabalho são apresentadas informações sobre túneis atribuídos a grandes mamíferos extintos. Essas
estruturas são encontradas em diversos locais do sudeste e sul do Brasil, ocorrendo em diferentes tipos de substratos,
desobstruídas (paleotocas) ou preenchidas por sedimentos (crotovinas). A paleotoca encontrada no município de Cristal
(RS) foi escavada nos depósitos de leques aluviais terciários e marcas de garras e impressões da carapaça podem ser vistas
ao longo da superfície interna da galeria. As dimensões da estrutura, as marcas de escavação e marcas de osteodermos
presentes ao longo das paredes da paleotoca sugerem que tenha sido produzida por um xenartro dasipodídeo. A comparação
com estruturas similares encontradas na Argentina pode fornecer informações mais detalhadas a respeito da paleoecologia e
bioestratigrafia dos organismos responsáveis por sua escavação.

The Coastal Plain of Rio Grande do Sul state (CPRS), in southern Brazil, is known for the presence of fossil accumulations containing remains of both marine and terrestrial Pleistocene organisms, in large biodetrital concentrations on the continental shelf and also in continental outcrops in Chuí Creek and Mangueira Lake. Many invertebrate remains exhibit bioerosion traces caused by endoskeletozoan organisms, while surface colonization by episkeletozoans is scarce. The ichno-traces Entobia and Caulostrepsis are the most common, followed by Pennatichnus, Gastrochaenolites and Maeandropolydora. Gastrochaenolites is found mostly in ostreids and Oichnus is mostly absent among fossils from the continental shelf and Passo da Lagoa, but is found in many bivalves from Chuí Creek. Ichno-traces identified as cf. Clionoides isp. are recorded for the first time among fossils from CPRS. Bioincrustation on invertebrates is very scarce, represented by cheilostomate bryozoans, ostreids and cirripeds. Among vertebrate remains found in the continental shelf, bioerosion has been recorded so far on three specimens; remains collected at greater depths are mostly covered by fouling organisms, including serpulid polychaetes and corals. While bioerosion is the predominant ichnological process affecting fossils from shallower areas, bioincrustation affects mostly remains found in deeper areas of the shelf. Ichnological differences among invertebrate fossils found in the continental shelf and those from outcrops in terrestrial environment seem to be related to marine transgressions and regressions that affected the area during the Late Quaternary.

Stable isotopes (δ13C, δ18O) in teeth of extinct mammals have been used as indicators of diets and climate conditions, which in turn are used for paleoenvironmental reconstructions. The first analysis of stable isotopes in Pleistocene mammals from Southern Brazil is reported here. The analyzed taxa were the notoungulate
Toxodon and the proboscidean Stegomastodon from Late Middle to Late Pleistocene fossiliferous beds exposed along Chuí Creek, in the coastal plain of Rio Grande do Sul State. The δ13C isotopes indicate that Toxodon was a mixed-feeder that fed mostly on C4 plants, while Stegomastodon was a browser to mixed-feeder with
preference for C3 plants, with less C4 plants in the diet compared to modern African elephants. Comparison with carbon isotopic values in fossils of these taxa from other Late Quaternary localities in South America shows an increased proportion of C3 plants in the diets of both Toxodon and Stegomastodon in higher latitudes. The values of δ18O in both taxa seem to reflect the isotopic composition of the ingested water rather than the
isotopic content in the plants of which they fed on, and the observed variations are likely to mirror variations of the patterns of precipitation. Paleoclimatic inferences and possible causes for the (pseudo)extinction of these taxa in southern Brazil are also discussed.

Ichnological features over fossil oysters from southern Brazilian coast are described herein. In the deposits Ostrea puelchana d’Orbigny, 1841 is the dominant oyster, followed by O. equestris Say, 1834 and Crassostrea virginica Gmelin, 1791. Although these taxa are found along the entire coast, they exhibit some geographical variations regarding the presence of borings. The most conspicuous ichnogenera are Caulostrepsis and Entobia, with Gastrochaenolites being common in fossils from the central sector of the coast, and scarce in the southern one. Maeandropolydora and incrustations (made by fouling organisms, e.g. cirripeds and bryozoans) are scarce. Most of the borings are found on the external side of the valves which suggest a dominant bioerosion activity during the life span of the organisms.

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 Chuí 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.

The present work presents the first occurrence of seabirdsʼ fossils from pleistocenic fossiliferous deposits submerged along the inner continental shelf of Rio Grande do Sul state. The fossils presented here were collected during field works between 1999 and 2003 and consist of three cervical vertebrae and a partial left tibiotarsus. The fossilsʼ morphology and size are similar to those of a procellariiform seabird of the Thalassarche melanophrys Temminck 1828 species (black-browed mollymawk). The fossils are well-preserved, indicating that were not subject to significant re-working during transport from the source areas to the beach. This suggests that the submerged deposits are located near the present shoreline.

"The fossiliferous deposits in the coastal plain of the Rio Grande do Sul State, Southern Brazil, have been known since the late XIX century; however, the biostratigraphic and chronostratigraphic context is still poorly understood. The present work describes the results of electron spin resonance (ESR) dating in eleven fossil teeth of three extinct taxa (Toxodon platensis, Stegomastodon waringi and Hippidion principale) collected along Chuı´ Creek and nearshore continental shelf, in an attempt to assess more accurately the ages of the fossils and its deposits. This method is based upon the analysis of paramagnetic defects found in biominerals, produced by ionizing radiation emitted by radioactive elements present in the surrounding sediment and by cosmic rays. Three fossils from Chuı´ Creek, collected from the same
stratigraphic horizon, exhibit ages between (42  3) Ka and (34  7) Ka, using the Combination Uptake model for radioisotopes uptake, while a incisor of Toxodon platensis collected from a stratigraphic level below is much older. Fossils from the shelf have ages ranging from (7  1) 105 Ka to (18  3) Ka, indicating
the mixing of fossils of different epochs. The origin of the submarine fossiliferous deposits seems to be the result of multiple reworking and redeposition cycles by sea-level changes caused by the glacial–interglacial cycles during the Quaternary. The ages indicate that the fossiliferous outcrops at Chuı´ Creek
are much younger than previously thought, and that the fossiliferous deposits from the continental shelf encompass Ensenadan to late Lujanian ages (middle to late Pleistocene)."

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.