Linxia Basin Research Articles

New specimens of anchitheriine from the Linxia Basin, Gansu and evolution of East Asian anchitheriines

Anchitheriinae are an extinct subfamily of the Perissodactyla family Equidae, the same family which includes modern horses, zebras and donkeys. Anchitheriinae are the most poorly studied of the Equidae. The distribution of anchitheriines in China has been recorded in Shanxi, Gansu, Inner Mongolia, Xinjiang, Hubei and Jiangsu in the early to middle, and the latest Miocene. Recently, some specimens of Anchitheriine have also been found in the Linxia Basin, Gansu. A specimen from the Wangjiashan locality was found to be a large-sized individual with complex morphology characteristic. The specimen was identical to the reported material of Sinohippus robustus from the same locality. Both specimens were very large size, had a distobuccal crest on the labial wall of p2, and displayed a deep and narrow ectoflexid perpendicular to major axis of the tooth. Based on these observations, the new specimen was identified as S. robustus . Specimens from the Laogou locality have been identified as Anchitherium gobiense in brief reports of the local fauna. Identification of the specimens was confirmed based on the complexity of diagnostic feature complexity such as medium size and characteristics of the lower cheek tooth row that progressively reduced from the middle to the ends. A detailed morphological analysis of these samples was performed on East Asian anchitheriines and compared to specimens from China and Japan. These observations confirmed a previous hypothesis that “ Anchitherium aurelianense ” from Fangshan, Nanjing, were more similar to Anchitherium gobiense , and should be considered as a different lineage from the true Anchitherium aurelianense found in Europe. The specimen from Fangxian, Hubei, was identified as Anchitherium gobiense from a previous research study. However, the size of the specimen was significantly larger than the Xinjiang specimens, and the holotype and the paratype specimens from Tunggur of Inner Mongolia. Two forms with obviously different sizes were also observed amongst the Tunggur specimens. The Fangxian specimen, and the larger from Tunggur were temporally attributed as Anchitherium gobiense type B. Based on morphological differences, Anchitherium aff. gobiense from the Kani Basin, Japan, are different from true Anchitherium gobiense and other forms found in Eurasia and considered to be Anchitherium hypohippoides in the present paper. The Japanese form has a less concave labial wall on the upper cheek tooth, which is a very primitive feature usually seen in ancestral forms found in North America, such as genus Kalobatippus. Eurasian anchitheriines were derived from North American Kalobatippus , and rapidly separated into the European and East Asian clades after they dispersed into Eurasia. The Japanese species Anchitherium hypohippoides, is the most primitive form, and different evolutionary stages were present in the Chinese clade over time. These stages are represented by “ A. aurelianense ” of Fangshan, A. gobiense group (including A. gobiense s. s. and Type B) and Sinohippus . Large species derived from Sinohippus occurred suddenly in China in the latest Miocene, showed gaps in both chronological and morphological transition. The origin of Sinohippus is unclear, but is a likely relative to a large form of Anchitherium sampelayoi in Europe. The first occurrence of latter come from Spain in about 11 Ma. An evolutionary trend was present in the East Asian anchitheriine clade, in which the body size of anchitheriines was firstly reduced and then increased. This is a normal phenomenon in Eurasian Equidea, such as Hipparion and Equus , and correlated to the demand of the animal itself for immigration, and the pattern of change in the climate and environment. Transcontinental immigration often depends on the connection of land bridges caused by drops in the sea level which eventually occur as a result of climate cooling. Large body size is advantageous in having resistance to cold and allows very long-distance immigration. In contrast, reduced body size can help to avoid fierce competition against other forms in similar niches and often results from warmer climates and increased richness of the community. With further improvement in the environment, the body size of anchitheriines may increase due to the improved availability of resources.

Cenogram analyses as habitat indicators for Paleogene–Neogene mammalian communities across the globe, with an emphasis on the early Eocene Cambay Shale mammalian community from India

The present study is an attempt to utilize cenogram methodology (both qualitative and quantitative) to consider mammalian communities from five early to late Eocene localities across the globe (i.e., Polecat Bench, Bighorn Basin, North America; Abbey Wood, Blackheath Formation, UK; Cambay Shale, Cambay Basin, India; Wutu Formation, Wutu Basin, China; Pondaung Formation, Myanmar) so as to provide a comparative palaeohabitat framework. It is also a first attempt to examine the palaeohabitat of an extinct mammalian community (i.e., from Cambay Shale) in India utilizing the cenogram approach. In addition, seven extinct middle-Miocene communities (Laogou, Linxia Basin, China; Estacion Imperial, Spain; Paseo de las Acacias, Spain; Arroyo del Olivar-Puente de Vallecas, Spain; Somo-saguas, Spain; Paracuellos 5, Spain; Paracuellos 3, Spain) have also been considered, in order to provide a global perspective to the climatic inferences in a temporal context. The majority of statistical calculations for Paleogene communities expose forested and humid conditions, excluding the Cambay Shale mammalian community of India. A hidden diversity within the medium to large body-size category of mammals (disguising the mammal biodiversity expected in tropical forested habitats) from Cambay Shale (western India) is a plausible cause of digression in the results. This is reflected in the histograms showing relationships between proportions of mammal species in various body-mass categories. Furthermore, the results show that Neogene mammalian communities were sustained in comparatively open habitats. Differences between occidental European and Asian localities in the canopy and humidity of the Neogene environments are also reflected in our analyses.

Evidence of Late Miocene Peri-Tibetan Aridification From the Oldest Asian Species of Sandgrouse (Aves: Pteroclidae)

The partial skeleton of a new extinct taxon, Linxiavis inaquosus, from the Liushu Formation (6-9 Ma) at the edge of the Tibetan Plateau in Gansu Province, China is the most substantial known fossil record of sandgrouse (Pteroclidae). While adding to the rapidly growing known Liushu avian fauna of vultures, falcons, pheasants, and ostrich, this new fossil is likely the oldest record of crown Pteroclidae (as a potential molecular clock calibration point), the oldest record of the group in Asia (from a probable African origin), and derives from a significant temporal gap in their Neogene history. The fossil specimen includes articulated and associated elements of the wings, shoulder girdle, vertebrae, and hind limb, exhibiting apomorphies of Columbiformes and Pteroclidae such as a notarium, and a short coracoid shaft. As part of the Linxia Basin’s diverse Hipparion fauna, Pterocles inaquosus reinforces the interpretation of the habitat as an arid savannah, associated with the uplift of the Tibetan Plateau. The holotype suggests that the arid high elevation Tibetan area habitats may have been continuously occupied since the late Miocene by sandgrouse carrying water in their modified breast feathers to their young.

Microbial communities and lipid records of the Linxia Basin, NE Tibetan Plateau: Implications for enhanced aridity in the Late Miocene

The Linxia Basin on the north-eastern Tibetan Plateau in northwest China bears continuous and thick lacustrine-fluvial sediments with environmental significance to central Asian aridification. However, limited efforts have been made on investigating the microbial community evolution, even though lipid biomarkers have been successfully employed to reconstruct paleoenvironmental conditions in this area. This study used the ancient DNA and n-alkanes preserved in the lacustrine-fluvial sediments from the Linxia Basin, and employed high throughput sequencing and geochemical analyses to understand the climatic conditions spanning the past 29 million years. The characteristics of n-alkanes indicate that the organic matter was derived from mixed sources (bacteria, algae, and higher plants), and a series of n-alkane proxies (ACL, n-C21−/n-C22+, Paq, and Pwax) established that the climate shifted to arid conditions at approximately 8 Ma. It is noteworthy that the relative abundance trends of two classes of microbes (Proteobacteria and Firmicutes) were negatively correlated. Furthermore, the increasing Firmicutes and the relatively decreasing Proteobacteria at approximately 8 Ma also corroborated this arid event. In addition, during this period, there was an extremely low abundance of archaea, which might correspond to severe climatic conditions around 8 Ma. Therefore, this study suggests that the microbial communities could serve as a potential tool for the reconstruction of paleoenvironments.

A new species of Eogruidae (Aves: Gruiformes) from the Miocene of the Linxia Basin, Gansu, China: Evolutionary and climatic implications

AbstractDespite having one of the most robust fossil records within core-gruiform birds (rails, cranes, and allies), the biogeographic history of Gruidae (cranes) and key drivers of diversification within this group remain largely unknown. The Eogruidae of Eurasia represent some of the earliest known crane-like fossils. Here, we present description of a new species represented by a well-preserved specimen of a foot from the late Miocene (7–6.5 mya) Liushu Formation of Linxia Basin, Gansu, China. It is the only eogruid fossil that has been found in this formation and is the first eogruid known from northwest China. Linxia Basin is located along the margin of the northeastern Tibetan Plateau, which allows for new insight into Miocene dispersal of the Eogruidae and potential climatological and geological connections. It is also the first specimen with an associated tarsometatarsus and nearly complete phalanges, including a claw, which provides further morphological information on this taxon. Referral of the new specimen to Eogruidae is based on extreme reduction of the trochlea of metatarsal II, which is most similar to the condition present in the eogruid subclade traditionally termed Ergilornithidae.

Isotopic record of palaeodiet of a 7.4 Ma Hipparionine fauna from the central Loess Plateau, northern China: Palaeo-ecological and palaeo-climatic implications

Ecological shifts from C3 to C4 vegetation took place in many parts of the world around 7.5–5 Ma in response to global climate change. Previous evidences from pollen, paleosol isotope, and faunal have suggested that the expansion of C4 vegetation also occurred in the central Chinese Loess Plateau (CLP) at 7.4 Ma, which, however, is incompatible with palaeoclimate evidence from the CLP of cold and dry conditions during the late Miocene. In this study, stable oxygen (δ18O) and carbon (δ13C) isotope ratios preserved in tooth enamel from hipparionine were analyzed to elucidate the late Miocene (∼7.4 Ma) palaeoecology of the central CLP. The enamel δ13C values indicated a diet comprised entirely of C3 plants, consistent with the C3 steppe inferred from the faunal composition for the western district of the Neogene palaeozoogeographical boundary of Northern China. The δ18O values were indicative of a mild continental climate with Late Miocene seasonality that is not as pronounced as the modern steppe environment of Mongolia. The local landscape was most likely dominated by C3 steppe which belonged to the western district of the Neogene palaeozoogeographical boundary of Northern China. Comparison of results presented here and with published records from other localities in this region such as the Linxia Basin, Yushe and central Inner Mongolia suggests a veer of the East Asian summer monsoon (EASM) since 7.5 Ma.

Magnetostratigraphic constraints on the age of the Hipparion fauna in the Linxia Basin of China, and its implications for stepwise aridification

Late Cenozoic sediments in the Linxia Basin of China, on the northeastern Tibetan Plateau, bear abundant fossils of the Hipparion fauna. From late Miocene times, these sections record a history of aridification in the Asian Interior, the evolution of the east Asian monsoon, and multiple uplifts of the Tibetan Plateau. In this paper, a new detailed magnetostratigraphic study of a sedimentary sequence from the Duikang (DK) section containing the Hipparion fauna is presented, to better understand interconnected ecologic and environmental changes. The 90-m-thick section reveals nine normal and nine reversed zones that span from chron. C5n.2n to chron. C3Ar or from chron. C4n.2n to chron. C2Ar, yielding magnetostratigraphic ages of ~8.1 Ma - 3.7 Ma for the studied section and 5.3 Ma for the Hipparion fauna-bearing bed. Combined with all the previous magnetostratigraphic ages of the fauna-bearing sediments in the Linxia Basin, Hipparion can be distinguished as mainly having lived during five periods: Phase I (11.5 Ma), Phase II (8.2 Ma), Phase III (6.3 Ma), Phase IV (~5.3 Ma) and Phase V (2.5 Ma). Based on comparison of climate records in the Linxia Basin with aridification records from surrounding regions and global cooling during the late Cenozoic, we suggest that the evolution of Hipparion from the Linxia Basin was mainly driven by continuous global cooling and tectonic uplift of the northeastern Tibetan Plateau since the late Miocene.

Evidence for early (≥12.7 Ma) eolian dust impact on river chemistry in the northeastern Tibetan Plateau

As one of the largest dust sources on the Earth's surface, dryland in Central Asia gives rise to thick eolian deposits over East Asia (e.g., the Chinese Loess Plateau, CLP) and significantly influences the regional hydrochemistry in the downwind drainage areas. However, the formation of thick eolian dust deposits requires not only climatic prerequisites for dust emission and transport but also climatic and topographic conditions favourable for deposition and accumulation. The scarcity of widespread eolian deposition around the CLP before 7-8 Ma hinders a full understanding of the processes and mechanisms of Central Asian aridification. The deposition of eolian dust also impacts the hydrogeochemistry of fluvial systems and the precipitation of authigenic phases in continental sedimentary systems could be an archive for studying eolian dust dynamics when pure eolian deposits are scarce. Here, we present the Ca-Mg-Sr concentrations and 87Sr/86Sr isotope compositions of bulk carbonates in a new fluvial sequence (12.7-4.8 Ma) of the Xining Basin. The Mg/Ca and Sr/Ca ratios of the carbonate describe a power law relationship with a power coefficient of ∼0.8, lower than the coefficient characteristic of prior calcite precipitation (PCP). An input of eolian dust with the dissolution of Mg-rich carbonate is likely responsible for the deviation from a pure PCP process. The bulk carbonates also show a general decrease of 87Sr/86Sr ratios from 12.7 to 4.8 Ma, with a transition around 8.6 Ma revealed by lower Sr/Mg ratios. The comparison of these proxies to a previously reported fluvial section (12.2-5.1 Ma) in the Linxia Basin, ∼200 km to the southeast, shows that the 87Sr/86Sr ratios of the bulk carbonates and water-soluble salts in the Linxia Basin are around 0.7098, which is 0.0018 lower than those in the Xining Basin before 8.6 Ma, but shows a significant rise between 8.6 and 7.0 Ma. The two basins share the same range of carbonate 87Sr/86Sr ratios when sediments are younger than 7 Ma. For the last 7 Myrs, the evolution of the 87Sr/86Sr ratios in bulk carbonates of fluvial sediments and Pliocene-Quaternary eolian deposits found in the Xining Basin are similar to those in typical eolian red clays/loess-palaeosol sequences on the CLP. These results suggest a transition of the hydrochemical regime at 8.6 Ma in the Linxia Basin from a catchment only influenced by the weathering of its bedrock to one significantly impacted by eolian dust input. In the Xining Basin, the carbonate elemental and 87Sr/86Sr ratios are consistent with a hydrochemistry more impacted by the presence of the eolian dust. There, the dust input occurred earlier, at ≥12.7 Ma, though it has strengthened since 8.6 Ma. The eolian dust impact on fluvial systems in the Xining Basin was much earlier than in the Linxia Basin and also preceded the initial accumulation of widespread eolian red clays on the CLP (7-8 Ma), suggesting a temporally propagating and spatially stepwise expansion of eolian dust delivery across the Asian inland during the late Cenozoic.

New paleomagnetic constraints for Platybelodon and Hipparion faunas in the Linxia Basin and their ecological environmental implications

Abstract The Linxia Basin in northwestern China lies topographically at the northeastern margin of the Tibetan Plateau and climatically at the western margin of the East Asian monsoon region, and bears abundant mammalian fossils with environmental significance on central Asian aridification and east Asian monsoon evolution. However, these mammals have not been precisely dated, hindering our ability to address the ecologic environment changes associated with the evolution of the Asian monsoon and multiple uplifts of the Tibetan Plateau. We present a detailed paleomagnetic study of a sedimentary sequence from the Laogou section in the Linxia Basin containing many mammalian fossils with ages ranging between middle and late Miocene. The 203 m thick section revealed 11 normal and 10 reversed zones that correlate well with chrons 3An to 5An of the Geomagnetic Polarity Time Scale, constraining its age to ~12.56–6.0 Ma, and suggesting that the middle Miocene Platybelodon fauna existed at about 11.5 Ma and the late Miocene Hipparion fauna occurred at about 6.4 Ma. These ages, combined with other magnetostratigraphic results from the whole basin, show that these two major mammal faunas lived during 12.5–11.1 Ma and 11.5–6.3 Ma in the Linxia Basin. The presence of well-developed floodplain paleosols, the color change of the fluviolacustrine sediments and the transition of large bodied mammals suggest that strong climatic and environmental changes happened in the Linxia Basin during late – middle Miocene, in the form of a transition from the warm and humid forest to the warm and subarid steppe at about 11.1 Ma.

Zebra layers and palaeoenvironment of Late Miocene Stratum in the Linxia Basin, northwestern China

Miocene strata in the Linxia Basin (Gansu, China) are usually interpreted as lacustrine sediments. However, the red–grey inter-beds known as ‘Zebra layers’ commonly tilt with respect to the terrain on the side slopes of the modern valley, which may be due to mantling palaeotopography (similar to aeolian loess). The anisotropy of magnetic susceptibility, which reflects the original arrangement of magnetic particles in sediments, was applied to investigate this phenomenon. The results showed that the tilting of the inter-beds in the side slope was due to mantle palaeotopography rather than soil creep, and that they were not deposited in a subaqueous environment. The grain sizes of sediments showed similar features as aeolian loess. We speculate that Miocene sediments were deposited by mantling the palaeotopography where aeolian materials accumulated. After deposition, flowing water submerged these strata, which caused the side slope to become gradually thinner from top to bottom and stirred the magnetic particles in these sediments. The grey colour of the Zebra layers may not be original, as it may be due to waterlogging and deoxidation after deposition; finally, when the iron oxides in these sediments were transformed or removed, their colours became grey. The formation of Zebra layers indicates that the Late Miocene palaeoenvironment of northwestern China was similar to that in which Quaternary aeolian loess was deposited.

Grain-size analysis of Upper Pliocene red clay deposits from Linxia Basin: Implications for Asian monsoon evolution on the NE margin of the Tibetan Plateau

Little is known about the evolution of the East Asian winter monsoon (EAWM) on the NE margin of the Tibetan Plateau (TP) during the late Pliocene-early Pleistocene, due to the poor exposure of pre-Quaternary eolian deposits and ambiguities in the interpretation of paleoclimatic proxies. In this study, we performed detailed grain-size analyses of eolian sequences (spanning 3.7–2.4 Ma) from two new boreholes in Linxia Basin, in the NE TP. We compared our results with contemporaneous loess-red clay sequences across the Chinese Loess Plateau (CLP) and identified a substantial decrease in the thickness and grain size of upper Pliocene-lower Pleistocene loess and red clay sediments from the western to central parts of the CLP. This observation supports the view that the grain size of upper Pliocene eolian sequences from Linxia Basin can be used to reconstruct the evolution of the EAWM. In addition, it demonstrates that the modern spatial pattern of the EAWM regime in the western CLP has been maintained since at least the late Pliocene. Records of both median grain-size (Md) and sand content from the boreholes exhibit an overall upward-increasing trend during the interval from ~3.7–2.4 Ma, indicating a long-term stepwise intensification of the EAWM and aridity on the NE margin of the TP. In addition, a dramatic coarsening of the grain size in loess unit L34 documents a large climatic shift at ~2.75 Ma, which may be closely linked with the major intensification of Northern Hemisphere glaciation during the late Pliocene.

Late Pliocene Monsoonal Rainfall Gradients in Western China Recorded by the Eolian Deposits From the Linxia Basin, NE Tibetan Plateau

AbstractLoess and red clay sediments from the Chinese Loess Plateau (CLP) contain a wealth of information about variations in the Asian monsoon and the aridification history of the Asian interior. However, relatively little is known about late Pliocene palaeoenvironmental evolution and the variations in the gradients of monsoonal rainfall in the western part of the CLP, due to the poor exposure of pre‐Quaternary eolian deposits and uncertainties in the interpretation of paleoclimatic proxies in most parts of the region. To address these issues, we conducted a detailed rock magnetic investigation of newly drilled eolian sequences (spanning 3.7–2.4 Ma) from the Linxia Basin, NE Tibetan Plateau. Our results demonstrate that pedogenically formed fine magnetic grains are responsible for the magnetic enhancement of loess‐red clay sediments from the basin. Spatially, a clear decrease in magnetic susceptibility and its frequency dependence is observed between the central and western CLP, indicating that the East Asian summer monsoon already exerted a major influence on the amount and distribution of late Pliocene rainfall in the Linxia Basin. After evaluating the validity of magneto‐climofunctions, we attempt to reconstruct late Pliocene‐early Pleistocene monsoonal precipitation in the NE margin of the Tibetan Plateau. The results demonstrate that the difference in late Pliocene monsoonal rainfall between the study area and Chaona in the central CLP was about 300–400 mm. This value is higher than that of the present day, indicating a steepened gradient in monsoonal rainfall between the central and western CLP during the late Pliocene.

A new record of late Pliocene-early Pleistocene aeolian loess–red clay deposits from the western Chinese Loess Plateau and its palaeoenvironmental implications

The loess–red clay sequences in northern China provide high-resolution terrestrial records of Asian monsoon evolution and aridification of the Asian interior. To date, however, aeolian deposits of late Pliocene-early Pleistocene age (3.5–2.4 Ma) have only rarely been reported from the western Chinese Loess Plateau (CLP), which significantly hinders our understanding of the distribution of aeolian deposits and the palaeoenvironmental evolution of the region. Here, we present magnetostratigraphic, lithologic and magnetic susceptibility results for two recently-drilled boreholes from the north bank of Baxie River, central Linxia Basin, which are highly correlative with those of the loess–red clay deposits spanning the interval from 3.6 to 2.4 Ma in the eastern CLP. Our results provide the first direct evidence for the occurrence of late Pliocene-early Pleistocene aeolian deposits in the western CLP and provide new insights into the distribution of aeolian deposits in northern China. The spatial coherence of the magnetic susceptibility fluctuations further indicates that magnetic susceptibility is a powerful tool for stratigraphic correlation of late Pliocene aeolian deposits in the western CLP. In addition, our results demonstrate that erosional events may have occurred in the early or middle Pleistocene, and they may provide new insights into the reasons for the absence of loess–red clay deposits from 3.5 to 2.4 Ma in most parts of the western CLP.

Topographic growth of the Jishi Shan and its impact on basin and hydrology evolution, NE Tibetan Plateau

AbstractPrevious research demonstrates that large basins on the periphery of the northern edge of the Tibetan Plateau were partitioned during development of intrabasin mountain ranges. These topographic barriers segregated basins with respect to surface flow and atmospheric circulation, ponded sediments, and formed rain shadows. However, complex mixing between airmasses and nonsystematic isotope‐elevation lapse rates have hampered application of quantitative paleoaltimetry to determine the timing of development of critical topographic barriers. We address the timing and drivers for changes in surface connectivity and atmospheric circulation in the Linxia and Xunhua basins using a multidisciplinary approach incorporating detrital zircon geochronology, Monte Carlo inverse flexural modelling, and published stable isotope data. Disruption of surface flow between the two basins during exhumation of the Jishi Shan preceded development of topography sufficient to intercept moisture‐bearing airmasses. Detrital zircon data point to disruption of an eastward‐flowing axial fluvial network between 14.7 and 13.1 Ma, coincident with the onset of exhumation in the Jishi Shan. Flexural modelling suggests that by 13 Ma, the Jishi Shan had developed 0.3 ± 0.1 km of relief; sufficient to disrupt eastward‐flowing drainage networks but insufficient to intercept moisture‐bearing airmasses. Stable isotope data indicate that, although surface connections between the Xunhua and Linxia basins were broken, the two basins continued to be dominated by a common climate regime until 9.3 Ma. Subsequent reintegration of surface flow between the basins occurred between 9.3 and 7.6 Ma. Divergence in the stable isotope and depositional environment records between the two basins suggests that at 9.3 Ma the paleo‐Yellow River breached the growing Jishi Shan dam, and may have reintegrated surface flow between the two basins via erosion of the modern Yellow River gorge, which transects the Jishi Shan. The reintegration of the Xunhua and Linxia basins’ surface connection is confirmed by reintroduction of a Songpan‐Ganzi flysch sediment source by 7.6 Ma. Continued exhumation and uplift of the Jishi Shan developed 0.8 ± 0.2 km of relief by ca. 8 Ma capable of intercepting moisture‐bearing airmasses; isolating and increasing aridity in the Xunhua Basin while decreasing it in the Linxia Basin. Our findings point to protracted development of the modern ca. 1 km of relief in the Jishi Shan between 14 and ca. 4.5 Ma followed by attainment of a topographic equilibrium which persists into modern times.

Magneto- and litho-stratigraphic records of the Oligocene-Early Miocene climatic changes from deep drilling in the Linxia Basin, Northeast Tibetan Plateau

The East Asian monsoon is generally regarded to have initiated at the transition from the Late Oligocene to the Early Miocene. However, little is known about this process because of a lack of continuous strata across the boundary between the Late Oligocene and the Early Miocene in Asia. Based on previous drilling (core HZ-1) in the Miocene sediments in the southern Linxia Basin in NW China, we drilled a new 620m core (HZ-2) into the Late Oligocene strata and obtained 206m of continuous new core. The detailed paleomagnetism of the new core reveals eleven pairs of normal and reversed polarity zones that can be readily correlated with chrons 6Bn-9n of the geomagnetic polarity time scale (GPTS), define an age interval of 21.6–26.5Ma and indicate continuity from the Late Oligocene to Early Miocene. The core is characterized by the remarkable occurrence of brownish-red paleosols of luvic cambisols (brown to luvic drab soils) above reddish-brown floodplain siltstones and mudstones, which suggest that the East Asian monsoon likely began by 26.5Ma. In contrast to the siltstone and mudstone of the Late Oligocene strata, the Miocene strata begin with a thick fine sandstone bed, which marks sudden increases in erosion and loading that most likely reflect a response to tectonic uplift. The hematite content and redness index records of the core further demonstrate that the monsoonal climate in the Late Oligocene to Early Miocene in this area was mainly controlled by global temperature trends and events.

Termination of fluvial-alluvial sedimentation in the Xining Basin, NE Tibetan Plateau, and its subsequent geomorphic evolution

The Xining Basin in northern China lies topographically in the transitional zone between the Tibetan Plateau and the Loess Plateau, and climatically in the transitional zone between humid East Asia and the arid Asian interior. During the Cenozoic, the basin accumulated a thick, continuous sequence of fluviolacustrine-dominated red beds and subsequent eolian loess. The termination of sediment deposition in the Xining Basin is the key to understanding its subsequent evolution, the development of the modern Yellow River, and the history of dust deposition. Here we present the results of a detailed paleomagnetic study of the upper sedimentary sequence of the Xining Basin below the river terraces, and in addition we review previous studies of river evolution development. Our results indicate that the age of the uppermost part of the continuous sequence of fluviolacustrine-dominated red beds in the Xining Basin ranges from ca. 20Ma to 4.8Ma, suggesting that basin sedimentation ended at the earliest at 4.8Ma, and they also provide an earliest age constraint for the subsequent river terrace development and eolian dust deposition. In addition, these results demonstrate that the termination of sedimentation in the Xining Basin and the nearby Linxia Basin was approximately coeval, suggesting the rapid regional tectonic uplift of the NE Tibetan Plateau and resulting reorganization of the landforms and development of the paleo-Yellow River in the late Pliocene.

Dietary reconstruction of Hezhengia bohlini (Artiodactyla, Bovidae) from the late Miocene Linxia Basin of China using enamel microwear

Dietary behavior of the middle late Miocene bovid Hezhengia bohlini from the Linxia Basin (Liushu Formation) of China was reconstructed using enamel microwear. Results were compared to a large comparative database of known ungulate microwear patterns. Results indicate a dietary regime that included both grass and browse. While scratch numbers reflect this heterogeneous dietary pattern, scratch width scores of H. bohlini are more typical of extant grazers. Also, enamel surfaces did not display the heavy pitting and large pits and gouges typical of extensive grit consumption indicating that fairly abrasive browse and/or grass was likely consumed. These results are consistent with paleohabitat reconstructions of the late Miocene Linxia Basin as mixed habitat including woodland/grassland mosaics.

A new species of Gomphotherium (Proboscidea, Mammalia) from China and the evolution of Gomphotherium in Eurasia

ABSTRACTGomphotherium is a stem taxon of Elephantida that was widespread in Africa, Eurasia, and North America during the Miocene. However, the evolution of this genus is greatly debated because of morphological variation among the species of Gomphotherium. In the present work, we describe a cranium and accompanying material of Gomphotherium from the late middle Miocene Hujialiang Formation of Linxia Basin, China. The new material shows dental similarities to G. subtapiroideum from the middle Miocene of Europe; however, it displays some cranial, mandibular, and dental feature combinations that are distinct from the known species of Gomphotherium. Therefore, a new species, G. tassyi, is established. We further study the phylogeny of Gomphotherium by cladistic analysis and recognize four groups. The most basal ‘G. annectens group’ is a paraphyletic group that includes G. annectens, G. cooperi, G. sylvaticum, and G. hannibali. The African taxa, G. libycum and G. pygmaeus, constitute a monophyletic group that has not been named. The ‘G. angustidens group’ is a monophyletic group that includes G. inopinatum, G. mongoliense, G. connexum, and G. angustidens. In addition, the ‘derived Gomphotherium group,’ which includes G. subtapiroideum, G. tassyi, G. wimani, G. browni, G. productum, and G. steinheimense, was widely distributed in Eurasia and North America during the middle and late Miocene.http://zoobank.org/urn:lsid:zoobank.org:act:28B89A74-7FF6-41DB-BA3C-C4CDD200A30FSUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: Wang, S.-Q., Y. Li, J. Duangkrayom, X.-W. Yang, W. He, and S.-Q. Chen. 2017. A new species of Gomphotherium (Proboscidea, Mammalia) from China and the evolution of Gomphotherium in Eurasia. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1318284.

Hipparion material from Gaojiashan locality in the Late Miocene of Linxia Basin, Gansu, China and associated mammalian fossil assemblage

Two Hipparion species, H. forstenae and H. hippidiodus from Gaojiashan locality in the Linxia Basin, Gansu, China are described in this paper, with the first presence of the former in the Linxia Basin. The lower cheek teeth of Hipparion from Gaojiashan bear deep ectoflexids, and after comparisons to other Chinese Hipparion fossils with deep ectoflexids, the mandibles with deep ectoflexids on the lower premolars suggest their attributions to H. forstenae. The presence of a deep ectoflexid on p2 may be interpretable as an intraspecifically variable feature in H. forstenae, and can also be found in H. dermatorhinum. Besides the Hipparion material, at least 8 species of large mammals occur at the Gaojiashan locality, including Adcrocuta eximia, Chilotherium wimani, Shansirhinus ringstroemi, Eucladoceros cf. proboulei, Palaeotragus cf. coelophrys, Giraffidae gen. et sp. indet., and the previously studied Promephitis hootoni and Eostyloceros hezhengensis. Although the sample from Gaojiashan shares five species with the Yangjiashan fauna, the Gaojiashan fossil assemblage may date to the Baodean because of the presence of H. forstenae. The overall taxonomic composition of the Gaojiashan assemblage at least suggests an approximate Baodean age, which would imply survival of C. wimani into the Baodean of the Linxia Basin.

A new species of Tetralophodon from the Linxia Basin and the biostratigraphic significance of tetralophodont gomphotheres from the Upper Miocene of northern China

Tetralophodont gomphotheres, i.e., Tetralophodon, Paratetralophodon, and Anancus, show significant morphological diversity and are of great importance for the biostratigraphy of the Upper Miocene. However, material of this group from the Upper Miocene of northern China is rare and easily to be confused with the similar taxa such as Konobelodon and Stegolophodon. The stratigraphy of this group is also unclear in China. Here we described the first mandible from northern China that can be definitely attributed to Tetralophodon, and erected a new species Tetralophodon euryrostris n. sp. Furthermore, we amended the previously reported tetralophodont gomphotheres from northern China. We attributed the type material of “Tetralophodon exoletus” to ?Paratetralophodon exoletus, the material from Lantian region (“Tetralophodon exoletus”) to Paratetralophodon sp., and the material from the Qaidam Basin (Tetralophodon sp.) to Tetralophodon aff. xiaolongtanensis. We also discussed the stratigraphic ranges of the tetralophodont proboscideans from the Upper Miocene of China, that is, Tetralophodon aff. xiaolongtanensis from MN9, Tetralophodon cf. euryrostris from MN10, Konobelodon robustus from MN9–MN10, Paratetralophodon sp. from MN11, ?Paratetralophodon exoletus from MN12, and Stegolophodon licenti from MN13. This work is important for the study of the taxonomy and biostratigraphy of tetralophodont gomphotheres from the Upper Miocene of northern China.