Late Pliocene-early Pleistocene Research Articles

On the last European giraffe, Palaeotragus inexspectatus (Mammalia: Giraffidae); new remains from the Early Pleistocene of Greece and a review of the species

Abstract Eurasian Giraffidae went through a drastic biodiversity decline after the Miocene–Pliocene boundary; scanty palaeotragine populations are likely to have survived in Central Asia, providing the necessary stock for a Late Pliocene–Early Pleistocene expansion from Central Asia to Spain and from the Mediterranean to southern Russia. Here, we describe new giraffid findings from the Greek middle Villafranchian faunas of Dafnero-3 and Volax and from the late Villafranchian faunas of Tsiotra Vryssi and Krimni-3, and we revise previous material from Dafnero-1. Our results support the synonymy of almost all the Villafranchian Eurasian giraffids under a single species of Palaeotragus, i.e. Palaeotragus inexspectatus, and allow us to improve its diagnosis. The orientation of the ossicones and the relative shortening of the lower premolar row might indicate affinities to some Late Miocene–Pliocene Palaeotragus from China. Our study suggests that P. inexspectatus was equally abundant at MNQ17 and MNQ18 in the Eastern Mediterranean and that its extinction after MNQ19 was probably attributable to the combination of the climatic and environmental turnover at the Villafranchian–Epivillafranchian boundary, along with the competition with emerging ruminant groups, such as giant cervids. A preliminary analysis of its palaeoecology suggests a giraffid more involved in grazing than its Late Miocene relatives.

Orbital- and millennial-scale Asian winter monsoon variability across the Pliocene–Pleistocene glacial intensification

Intensification of northern hemisphere glaciation (iNHG), ~2.7 million years ago (Ma), led to establishment of the Pleistocene to present-day bipolar icehouse state. Here we document evolution of orbital- and millennial-scale Asian winter monsoon (AWM) variability across the iNHG using a palaeomagnetically dated centennial-resolution grain size record between 3.6 and 1.9 Ma from a previously undescribed loess-palaeosol/red clay section on the central Chinese Loess Plateau. We find that the late Pliocene–early Pleistocene AWM was characterized by combined 41-kyr and ~100-kyr cycles, in response to ice volume and atmospheric CO2 forcing. Northern hemisphere ice sheet expansion, which was accompanied by an atmospheric CO2 concentration decline, substantially increased glacial AWM intensity and its orbitally oscillating amplitudes across the iNHG. Superposed on orbital variability, we find that millennial AWM intensity fluctuations persisted during both the warmer (higher-CO2) late Pliocene and colder (lower-CO2) early Pleistocene, in response to both external astronomical forcing and internal climate dynamics.

Astronomically forced climate evolution in the North China Plain since the Late Pliocene

Under the background of global warming, the impact of climate change in the densely populated North China Plain is becoming increasingly prominent. Cenozoic deposits in this area can provide insights into the evolution of the monsoon and the associated climate changes. This study focused on the SYZK01 borehole in the Beijing Plain area, primarily consisting of fluvial-lacustrine sediments. By employing detailed magnetic stratigraphy and multi-dating methods, we determined the age of the deposits to be approximately 0–3.3 Ma. Grain size and spontaneous potential logging were selected as proxies for paleoclimate. Our results reveal a strong coupling between the 0.063–0.25 mm grain size component, spontaneous potential logging and deep-sea δ18O in the overall sediment, confirming that glacial-interglacial cycles are the most significant form of climate change affecting the sedimentation process in the North China Plain. We observed a dominant 100 kyr eccentricity cycle within the 0.063–0.25 mm grain size component through the spectral analysis of the time-domain series of grain size indicators. In comparison, the 41 kyr cycle exhibited significant influence only from 1.1 to 0.6 million years ago. Notably, our study highlights that the SYZK01 borehole records the “late Pliocene-early Pleistocene 100 kyr problem,” characterized by phase and amplitude variations that do not align with Earth's orbital eccentricity.

Obliquity forcing of Late Pliocene–Early Pleistocene aridification in the Qaidam Basin, NE Tibetan Plateau

Knowledge of the variations of aridification during past warm periods can help predict future aridification trends. However, the variation of aridity during the warm Pliocene epoch, a potential analog for the future climate, has not been sufficiently studied due to the lack of high-resolution records. Here, we present high-resolution (∼7 kyr) oxygen and carbon isotope records spanning the Late Pliocene–Early Pleistocene from the Qaidam Basin, northwestern China. We interpret enriched carbonate δ18O value as indicating stronger evaporation, based on the general correlation between the enrichment of carbonate δ18O and an increased sedimentary halite content. Our results reveal that the Qaidam Basin was already an extremely arid environment no later than ∼3.9 Ma, and that aridification was further intensified at ∼2.6 Ma. Interestingly, the Qaidam Basin experienced decreased aridity or climate wetting during the high insolation intervals within the middle Piacenzian warm period, in contrast with the intensified aridity in the semi-arid Chinese Loess Plateau. Strikingly, the Qaidam Basin experienced intensified aridification during high-obliquity intervals, with smaller global ice sheets, during 3.6–2.5 Ma. We attribute this obliquity signal of Asian aridification to the effects of insolation and possibly glacial forcing, via their impacts on regional evaporation and reduced monsoon precipitation. Using the Late Pliocene as an analogue, our findings suggest that future aridification variations in Central Asia during the next ∼100 kyr may be dominated by 40-kyr cycles, under natural climatic forcing.

Late Neogene terrestrial climate reconstruction of the central Namib Desert derived by the combination of U–Pb silcrete and terrestrial cosmogenic nuclide exposure dating

Abstract. The chronology of the Cenozoic “Namib Group” of the Namib Desert is rather poorly understood and lacks direct radiometric dating. Thus, the paleoclimate and landscape evolution of the central Namib Desert remains imprecise, complicating the detailed search for global and/or local forcing factors for the aridification of the Namib. The widespread occurrence of calcretes and silcretes in the Namib Desert allows us to apply the novel application of the U–Pb laser ablation dating technique on silcretes and calcretes to date important phases of landscape stability and to retrieve critical paleoclimatic and environmental information on desertification and its paleoclimatic variability. Microscale silcrete formation (maximum of 8 mm) due to pressure solution by expanding calcrete cementation provides the opportunity to date multiple phases (multiple generations of silcrete as growing layers or shells) of silcrete formation. Groundwater silcrete and calcrete formation occurred at our study site during the Pliocene, a period of relatively stable climate and landscape conditions under semi-arid to arid conditions. Terrestrial cosmogenic nuclide (TCN) exposure ages from flat canyon rim surfaces indicate the cessation of groundwater calcrete formation due to incision during the Late Pliocene–Early Pleistocene and mark a large-scale landscape rejuvenation due to climate shifts towards more arid conditions in the Pleistocene, which can be connected to global climate patterns. This study demonstrates the feasibility of applying U–Pb laser ablation to groundwater silcrete and calcretes, discusses several important issues associated with this technique, and opens up the possibility of dating numerous sedimentary sequences containing silcretes and calcretes in arid environments. In particular, the use of silcretes (as described above) reduces potential effects of detrital components and bulk signal measurements by using massive calcretes. Our study redefines and improves the generally accepted Late Cenozoic chronostratigraphy of the Namib Desert (Miller, 2008).

Competing influence of the Taiwan orogen and East Asian Summer Monsoon on South China Sea paleoenvironmental proxy records

Late Cenozoic changes in the intensity of the East Asian Summer Monsoon (EASM) are reconstructed using both terrestrial and marine proxy records; however, proxies from terrestrial (e.g., loess, pollen, and pedogenic isotopes) and marine environments (e.g., foraminifer assemblages and geochemistry) commonly display large discrepancies both in the direction and timing of changes in the EASM. In part, these discrepancies reflect long-term changes in paleogeography that are independent of climate variations. We assess the influence of a rapidly uplifting orogen on EASM records by comparing temporally constrained gamma-ray, δ13Corg, hematite/goethite, and magnetic susceptibility records from Late Miocene–Early Pleistocene strata of the Taiwan Western Foreland Basin to time-equivalent EASM proxy records in the South China Sea (SCS).Prior to the emergence of modern Taiwan (∼6.3–5.4 Ma), sediment in the SCS was largely derived from Eurasia and transported into the Pacific Ocean. Following its emergence and southwest migration of the collision zone ∼5.4 Ma, proto-Taiwan became a major sediment source to the SCS. The uplift and southwest migration of Taiwan and northwest migration of the Luzon volcanic arc resulted in the formation of southwest-flowing deep- (1500–2500 m water depth) and bottom-water (>2500 m water depth) currents and the SCS Branch of the Kuroshio Current. Together these currents transported sediment from Taiwan towards the SCS. Increased sediment input from Taiwan is recorded as a decline in hematite/goethite values in sediment records from the northern and central SCS. By ∼3.2 Ma, continued southwest migration and growth of the Taiwan orogen resulted in the formation of the Taiwan Warm Current, which remobilized some sediment from Taiwan towards the East China Sea. Despite strengthening of deep-water currents during the Late Pliocene–Early Pleistocene, relative sediment input from Taiwan to the wider SCS decreased. Consequently, relative contributions from Eurasia and Luzon increased. In the southern SCS, where the Mekong River has dominated sedimentation since the Late Miocene, proxy records show no influence from the Taiwan orogen and instead reflect environmental changes in Mainland Southeast Asia driven mainly by monsoon variability.Our results show that a rapidly uplifting orogen has the potential to significantly impact paleoclimate records >1000 km away from the collision zone. This highlights the influence of shifting sediment sources on paleoclimate proxy records, which must be considered in interpreting past climate change from the sedimentary record.

Plio-Pleistocene rear-arc volcanism in the Southern Volcanic Zone: Eruptive styles of the Varvarco Volcanic Field

The Varvarco Volcanic Field (VVF) is located in the southern part of the Las Loicas Trough, as part of the Late Pliocene-Early Pleistocene rear-arc volcanic belt in the Transitional Southern Volcanic Zone (34.5–37°S). Its volcanic products show an elliptical distribution, elongated parallel to NW-SE main structures that regionally controlled the Las Loicas Trough. A detailed field and petrographic study was carried out to identify main lithofacies and establish its eruptive styles.The VVF magmatic evolution is initially characterized by a voluminous explosive stage represented in the area by dense and dilute pyroclastic density currents (PDC) deposits (massive lapilli tuffs, cross-stratified lapilli tuffs and diffuse-stratified tuffs). Afterwards, it evolved into an effusive stage represented by basaltic lava flows (coherent basalts), associated with Hawaiian to Strombolian eruptive style, which constitutes most of the VVF volume. The final stage of the VVF history was linked to a stratovolcano-type activity where both effusive (coherent basalts and andesites, and rhyolitic coulees) and explosive lithofacies (such as massive lithic breccias and massive lapilli tuffs) are described. Within this stage, the uppermost effusive levels were intruded by dacitic and rhyolitic domes and basaltic dykes. Available ages allow to conclude that the VVF emplacement was developed during Plio-Pleistocene times, linked to the re-steepening of the Nazca plate, after the Late Miocene Payenia shallow subduction regime.

Arbacia ballenensis sp. nov. (Echinoidea, Arbacioida): A new species reveals diversification of the genus in Central America.

A new species of Arbacia (Echinoidea, Arbacioida), A. ballenensis sp. nov., from the Late PlioceneEarly Pleistocene of Baja California Norte, Mxico, is described from a series of 62 specimens ranging in size from 6 to 20 mm test diameter. It differs from all extant species in the genus by its high number of interambulacral plates, numerous small interambulacral tubercles, and the size of the interambulacral tags at the peristomial edge. This new species yields new evidence concerning the diversification of the genus along the Pacific coast of North America where previously, only one extinct species was described, Arbacia abiquaensis from the Oligocene of Oregon. A. ballenensis sp. nov. is closely related to the recently described Arbacia quyllur from the late Miocene of Chile. Study of the new species in the context of events such as the mid-Pleistocene Transition helps shed light on patterns of extinction and speciation within the genus.

A New Species of Sandgrouse (Aves: Pteroclidae) from the Early Pleistocene of the Crimea.

Sandgrouse (Pteroclidae, Pterocliformes) are specialized ground birds of open arid landscapes with a very poorly studied evolutionary history. In the late Pliocene-early Pleistocene, Pteroclidae are known only from few localities in Southern Europe. The article describes a relatively large fossil sandgrouse from the early Pleistocene of the Taurida cave in the Crimea. This is the first record of Pteroclidae in the ancient faunas of the Black Sea region and Eastern Europe. The unusual structure of the tibiotarsus makes it possible to describe the fossil form from Taurida Cave as a new species, Pterocles bosporanus sp. nov.

Multi‐proxy evidence for rapidly shifting sediment sources to the Taiwan Western Foreland Basin at the Miocene–Pliocene transition

AbstractThe Taiwan Western Foreland Basin is thought traditionally to have received sediment mainly from Eurasia until the late Pliocene–early Pleistocene, after which time, the Taiwan orogen became the dominant source. However, a combination of clay mineralogy, δ13Corg and C/N of organic matter, and mass‐specific magnetic susceptibility of late Miocene to early Pliocene strata of the Kueichulin Formation indicate that onset of major sediment contributions from Taiwan occurred much earlier, and correlates closely to the uplift and initial emergence of the Taiwan orogen. Clay mineralogy shows an upsection increase in illite and illite crystallinity, and a decrease in chlorite and kaolinite after the late Miocene, and this is attributed to rapid erosion of the Taiwan orogen. Results from δ13Corg and C/N analyses show that organic material in the Kueichulin Formation changed from dominantly marine to dominantly terrestrial in the early Pliocene, and this is linked to the delivery of large quantities of terrestrial organic material from the Taiwan orogen to the adjacent Taiwan Strait. Magnetic susceptibility also decreases significantly during the early Pliocene, resulting from dilution of magnetic minerals through the influx of non‐magnetic minerals delivered from the Taiwan orogenic belt. The establishment of the growing Taiwan orogen as a major sediment source to the Western Foreland Basin occurred at the Miocene–Pliocene transition, about two million years earlier than previously recognized.

New insights on the fossil arc of the Tyrrhenian Back-Arc Basin (Mediterranean Sea)

Geology, geophysics and geodynamics of the Tyrrhenian Back-Arc Basin (BAB; central Mediterranean Sea) have been studied extensively during the last 50 years. However, some topics are still open: for example, the possible migration of the volcanic arc during the Ionian subduction of the past few Ma. We improved our knowledge of the geodynamics of the Tyrrhenian BAB in the area South of the Vavilov Volcano by analyzing multibeam bathymetry and unpublished single-channel reflection seismic and magnetic data. Furthermore, we studied the petrology of igneous rocks as well as facies and microfaunas of carbonates dredged from the Aurelia and Augusto seamounts. The Aurelia basement is made of basalts with calc-alkaline affinity. Carbonates from the Aurelia and Augusto seamounts consist of cemented Mg-calcite biomicrite crusts rich in planktonic foraminifera not older than Early Pleistocene. Based on our results, we interpret the Augusto and Aurelia seamounts as part of the active volcanic arc seaward of the Tyrrhenian BAB in Late Pliocene–Early Pleistocene.

GEOLOGY OF PONELO REGION AND SURROUNDINGS, NORTH GORONTALO REGENCY

The research area is one of the islands in the District of Ponelo Islands, North Gorontalo Regency, Gorontalo Province. This study aims to determine the geological conditions of the area using the geological mapping method. The results showed that the geomorphology of the study area was divided into 3 units, namely Lava Flow Hills, Denudasional Hills, and Marin Plains. The stratigraphy of the research area is divided into 5 unofficial units sorted from oldest to youngest, namely Sandstone Unit, Conglomerate Unit, Porphyry Andesite Unit, Basalt Lava Flow Unit (Late Pliocene-Early Pleistocene), and Coastal Sediment Unit (Recent age). The geological structures observed were Shear Fracture, Tension, Sheeting Joint, and Columnar Joint. The geological history of the research area starts from the Late Pliocene to Early Pleistocene where the Lokodidi Formation and Pinogu Volcano Formation were formed, resulting in sandstone and conglomerate units (Lokodidi Formation), porphyry andesite units and basalt lava flow units (Pinogu Volcano Formation). Then the alluvial deposition process which is still ongoing today is the result of weathering of rocks in the research area.

New well-preserved materials of Glossotherium chapadmalense (Xenarthra, Mylodontidae) from the Pliocene of Argentina shed light on the origin and evolution of the genus

ABSTRACT Fossil remains of extinct mylodontine sloths have been discovered in numerous localities throughout the American supercontinent, but knowledge of them is still mainly centered on the Pleistocene forms rather than their Neogene relatives. In this contribution, previously unpublished cranial and postcranial materials herein ascribed to Glossotherium chapadmalense (Kraglievich), coming from the Pliocene Chapadmalal Formation (Province of Buenos Aires, Argentina), are presented. These remains are described and compared with those of other mylodontine species from South and North America, providing an exhaustive characterization of cranial morphology in G. chapadmalense and some preliminary insights into its postcranial anatomy. The results have revealed a unique combination of differences and similarities of this enigmatic species with the larger-sized representatives of Glossotherium. In addition, these materials allowed shedding light on the long-standing uncertainties regarding its taxonomic status, as this form has been alternately considered to belong to the genera Glossotherium or Glossotheridium over the last century. As a result, the genus Glossotherium was present, at least, at the Early–Late Pliocene transition in the Pampean region of Argentina, and is recorded by the Upper Pleistocene throughout the entire South American continent. The radiation of the Pleistocene species is associated with a consistent body mass increase that was probably a response to the cooling temperatures and higher predation pressure in South America during the Late Pliocene–Early Pleistocene. These phenomena were probably driven by the stable emergence of the Panamanian Isthmus around 3 Ma and the successive faunal turnover pulses of the Great American Biotic Interchange.

Late Pliocene–Early Pleistocene ichnofauna from bentonitized tuff band and associated mudstone horizons, Jammu and Kashmir, India, and their palaeoenvironmental implications

Late Pliocene–Early Pleistocene ichnofauna from bentonitized tuff band and associated mudstone horizons, Jammu and Kashmir, India, and their palaeoenvironmental implications

Canids (Caninae) from the Past of Venezuela

There are three extant species of wild canids in Venezuela: Urocyon cinereoargenteus, Cerdocyon thous, and Speothos venaticus, excluding the feral domestic dog (Canis familiaris). However, a review of paleontological material that was published previously, along with newly reported ancient specimens, reveals a distinct historical diversity for the same region. The gray fox, U. cinereoargenteus, is the only small-sized taxon and the only Vulpini (true fox) identified to date in the fossil record of Venezuela; its presence is limited to the late Pleistocene of the Mene de Inciarte site, Zulia State. In contrast, large canids are more abundant. Aenocyon dirus (subtribe Canina), the dire wolf from the late Pleistocene, was reported from the sites El Mene de Inciarte, Muaco in Falcón State, and for the first time in El Breal de Orocual (ORS20) in Monagas State. The genus Protocyon, a native South American canid (subtribe Cerdocyonina), is recognized in the country from late Pleistocene Inciarte (Protocyon troglodytes sensu lato), and late Pliocene–early Pleistocene Orocual (ORS16) (Protocyon orocualensis sp. nov.). Finally, we report a possible genus Theriodictis from the late Pleistocene Orocual; this is a Cerdocyonina not previously mentioned for the northern region of South America. These records present broader diversity and suggest a more complex evolutionary history than previously thought for South American canids.

Palaeoceanographic changes in the late Pliocene promoted rapid diversification in pelagic seabirds

AbstractAimPalaeoceanographic changes can act as drivers of diversification and speciation, even in highly mobile marine organisms. Shearwaters are a group of globally distributed and highly mobile pelagic seabirds. Despite a recent well‐resolved phylogeny, shearwaters have controversial species limits, and show periods of both slow and rapid diversification. Here, we explore the role of palaeoceanographic changes on shearwaters' diversification and speciation. We investigate shearwater biogeography and the evolution of a key phenotypic trait, body size, and we assess the validity of their current taxonomy.LocationWorldwide.TaxaShearwaters (Order Procellariiformes, Family Procellariidae, GeneraArdenna,CalonectrisandPuffinus).MethodsWe generated genomic (ddRAD) data to infer a time‐calibrated species tree for the shearwaters. We estimated ancestral ranges and evaluated the roles of founder events, vicariance and surface ocean currents in driving diversification. We performed phylogenetic generalised least squares to identify potential predictors of variability in body size along the phylogeny. To assess the validity of the current taxonomy, we analysed genomic patterns of recent shared ancestry and differentiation among shearwater taxa.ResultsWe identified a period of high dispersal and rapid speciation during the Late Pliocene–early Pleistocene. Species dispersal appears to be favoured by surface ocean currents, and founder events are supported as the main mode of speciation in these highly mobile pelagic seabirds. Body mass shows significant associations with life strategies and local conditions. The current taxonomy shows some incongruences with the patterns of genomic divergence.Main ConclusionsA reduction of neritic areas during the Pliocene seems to have driven global extinctions of shearwater species, followed by a subsequent burst of speciation and dispersal probably promoted by Plio‐Pleistocene climatic shifts. Our findings extend our understanding on the drivers of speciation and dispersal of highly mobile pelagic seabirds and shed new light on the important role of palaeoceanographic events.

Detailed Processes and Potential Mechanisms of Pliocene Salty Lake Evolution in the Western Qaidam Basin

Hyperarid climate and salty lakes prevail in the current Qaidam Basin, but this basin was once a large paleolake until the early Quaternary. However, its evolution history and relationship with climate and tectonics are still elusive. Here we present detailed stratigraphic descriptions combined with total organic carbon content and weight ratio of organic carbon to total nitrogen records from fluvio-lacustrine sediments in the western Qaidam Basin to infer how the lake evolved during the late Pliocene-early Pleistocene. These data reveal a drying trend since 3.3 Ma, which we attribute to low latitude forcing and/or local tectonic activities. However, this trend was interrupted during 2.84–2.48 Ma, in which climate wetting was observed. We attribute the climate wetting during 2.84–2.48 Ma to intensified East Asian summer monsoon as is documented by the Chinese Loess Plateau records. Halite and gypsum content increased dramatically after 2.5 Ma, indicating the formation of salty lake in the western Qaidam Basin. These data improve our understanding of the detailed processes of Qaidam aridification and its potential forcing mechanisms.

A new Toxodontidae (Mammalia, Notoungulata) from the upper Pliocene–lower Pleistocene of Uruguay

ABSTRACT A specimen of Toxodontidae from the upper Pliocene–lower Pleistocene of Uruguay is studied in this paper. The material consists of associated skull and mandibular fragments previously identified as Dinotoxodon paranensis. The full description of the specimen, its comparison with different notoungulates, and a phylogenetic analysis are performed. According to the obtained results, Charruatoxodon uruguayensis, gen. et sp. nov. is recognized as a new taxon with unique features such as nasals compressed laterally, somewhat convex in transversal and longitudinal planes, incisive foramina deep and rounded, and other characteristics shared with several taxa of Toxodontidae. The mandibular expansion, present in the studied material, formerly used as a diagnostic character of D. paranensis (also present in Gyrinodon quassus, Pericotoxodon platignathus, and Hoffstetterius imperator), does not constitute a synapomorphy for these taxa as it appears to have evolved independently in different lineages according to our phylogeny. The new taxon is a medium-sized toxodontid more closely related phylogenetically to Toxodon platensis and D. paranensis than to other toxodontids. The family Toxodontidae constitutes a natural group. The clades within this group do not correspond to the subfamilies classically considered within the family, agreeing with later results. The new late Pliocene–early Pleistocene taxon from the Raigón Formation adds to the endemic fauna from Uruguay.

Astronomical forcing of vegetation and climate change during the Late Pliocene–Early Pleistocene of the Nihewan Basin, North China

The Late Pliocene–Early Pleistocene is an important transitional period in the Cenozoic evolution of global climate and environment. Previously, we demonstrated the occurrence of distinct cycles in vegetation and climate in the Nihewan Basin, during 2.89–1.78 Ma. However, the specific cycles and their forcing mechanisms were not studied more in-depth. Here we present the results of wavelet and spectral analyses of pollen percentages (Picea, Pinus, xerophytic taxa and broadleaved trees), macro-charcoal concentration, clay % and sand %, and magnetic susceptibility of 340 samples from the NHA drill core in the Nihewan Basin, during 2.89–1.78 Ma. The results reveal dominant ~20-kyr and ~40-kyr cyclicities: the pollen percentages of Pinus and broadleaved trees, magnetic susceptibility, and clay %, indicating a warm and humid climate, are more significantly influenced by ~20-kyr; in contrast, the percentages of Picea and xerophytic taxa, macro-charcoal concentration, and sand %, associated with a cold and dry climate, are mainly influenced by ~40-kyr. The ~20-kyr and ~40-kyr cycles corresponding to the dominant cycles of the East Asian summer monsoon and winter monsoon, which are respectively driven by Earth orbital precession and tilt, indicating that vegetation and climate change in the Nihewan Basin during 2.89–1.78 Ma was forced by a combination of low- and high-latitude processes. Otherwise, most of the proxy indexes also show a pronounced ~100-kyr cycle, which may be a response to changes in Northern Hemisphere ice sheets, emphasizing the importance of high-latitude forcing of vegetation and climate change in the Nihewan Basin.

New craniodental material of the extinct sigmodontine Olympicomys (Rodentia, Cricetidae) allows a discussion of its tribal affiliation

ABSTRACT We re-evaluate the tribal allocation of Olympicomys vossi, an extinct member of Sigmodontinae (Rodentia, Cricetidae). Originally described from fragmentary jaws, this taxon was considered as a Phyllotini. In light of new remains, including hemimandibles and for the first time an anterior part of the cranium with the upper dentition, we propose that it belongs to the Reithrodontini. The studied materials were collected in coastal outcrops of the Vorohué Formation (late Pliocene-early Pleistocene) south of Mar del Plata, Buenos Aires Province, Central Argentina. The reallocation of Olympicomys into Reithrodontini is based on the presence in this genus of several diagnostic characters of this tribe including a deeply excised anterior border of the zygomatic plate, a well-developed zygomatic spine, a shallow area of insertion of the anterior deep masseter muscle, a posteriorly depressed palate, labial accessory roots on upper and lower first molars, three-rooted lower third molar, and a bifid metaflexus on the second upper molar. Chukimys favaloroi and Dankomys vorohuensis, two other Pliocene Argentinean sigmodontines, are suggested as extinct reithrodontines. The restudy of Olympicomys provides elements to discuss the pattern of radiation of Sigmodontinae and to improve the chronostratigraphy of the coastal Neogene sedimentary succession of the Buenos Aires province.