Journal of Quaternary Science最新文献

The vertebrate assemblage recovered from the Toropí/Yupoí Formation (Late Pleistocene) in the Arroyo Toropí area, Bella Vista (Corrientes Province, Argentina), has been subjected to taphonomic evaluation. The fossil-bearing levels have been dated to ~53 ka (MIS 3) based on Optically Stimulated Luminescence dating. This assemblage primarily comprises mammal remains, with a notable prevalence of herbivorous megamammals. Also, reptiles and birds have been documented. Sedimentological analysis suggests that the skeletal remains were preserved within a floodplain environment influenced by the dynamics of the adjacent fluvial system, and taphonomic features observed in the assemblage support this interpretation. The assemblage resulted from the deposition of disarticulated mammal remains and local dispersion over a relatively short period. Rapid burial is evident, but several processes such as weathering and breakage have contributed to the observed patterns. The loss of several skeletal elements within the assemblage may be attributed to sporadic water flows occurring on the floodplain. During the post-burial stage, the specimens were affected by diagenetic processes, including filling, impregnation, deformation and breakage. In summary, the taphonomic evaluation of the Toropí/Yupoí Formation offers valuable comparison with other fossil fluvial assemblages. This research contributes to our understanding of the processes and environmental conditions that shaped this Late Pleistocene ecosystem.

The response of aquatic ecosystems in the Sierra Nevada (California, USA) to late Quaternary hydroclimate changes remains mostly unknown. Mono Lake, a large endorheic lake just east of the Sierra Nevada, contains an expanded archive of laminated sediments that can be used to examine the response of benthos to environmental changes. Fossil ostracodes from a radiocarbon-dated core were used to examine paleoecologic changes from ~16.6 to 4.3k cal a bp. Seven species were identified, with the co-occurrence of Limnocythere ceriotuberosa and Limnocythere staplini indicating a large SO₄²⁻-rich lake in the Pleistocene. The Younger Dryas was complex, with Fabaeformiscandona caudata reflecting a cold and deep lake ~13.0–12.2k cal a bp, followed by an interval of extensive littoral habitat from ~12.2–11.6k cal a bp. Ostracode diversity, valves g^–1 and the ratio of adult:juvenile valves declined after ~10.7k cal a bp due to regression, altered hydrochemistry and seasonal anoxia. Strong seasonality during the Early Holocene is suggested by the presence of reworked ostracodes and macrocharcoal, delivered to Mono Lake by erosion of ancient lake beds in the basin. A depauperate ostracode fauna in the Middle Holocene suggests a strong sensitivity to drought in this ecosystem, which has implications for biodiversity in the future.

While humic lakes are common in northern Europe, in central Europe they are rare and our understanding of their ontogeny is insufficient. Here, we present the reconstruction of the development of a humic lake in the Tatra Mountains (Slovakia) over the last 8000 years using chironomids along with diatoms, pollen and non-pollen palynomorphs. The compositional changes in aquatic proxies suggest three developmental stages. Since its formation the lake has been oligotrophic (phase 1), and its chemistry was controlled by subsurface waters rich in base cations buffering the effect of acid humic substances from forest and peat that were already present in the catchment. The beginning of the transition to phase 2 (~4400 cal a bp) is marked by simultaneous alterations in all proxies. Climate change combined with the local geochemistry was able to alter the limnological conditions supporting unique chironomid assemblages that have no analogues in recent Carpathian lakes. At ~3400 cal a bp the lake shifted to a phase when acidophilic/acidotolerant taxa indicate characteristic humic lake conditions (phase 3). Some chironomid taxa appearing ~2000 years ago for the first time indicate a dystrophic state in which the lake has remained until now. Human activities have been detected in the area since the Aeneolithic but had no direct influence on the lake.

Knowledge of bone pathologies in South American native ungulates is very scarce, which contrasts with other groups of megamammals such as xenarthrans and proboscideans. In this paper, based on morphological and histological analysis, we describe different bone pathologies in two specimens of Toxodon platensis Owen (Notoungulata), one of the most common taxa in the Late Pleistocene faunistic associations of northeastern Argentina. Subchondral erosions on the metacarpus and magnum, non-marginal syndesmophytes and enthesitis on the vertebral body, the neural column and the zygapophyseal joint of the lumbar vertebrae, as well as a particular periosteal reaction on the ribs, have been interpreted as manifestations of spondyloarthropathies in one of the analyzed individuals. In the same individual, a process of fusion and bone neoformation is observed in the caudal vertebrae, which seems to correspond both to the aforementioned spondyloarthropathy and to an infectious process. A lesion on the fourth metatarsus of a second individual with an evident cloaca is suggestive of osteomyelitis; this is the first report of this pathology in notoungulates. It seems possible that some of these pathologies may have been facilitated by factors such as body mass, mode of locomotion and/or environment. These findings provide insight into some aspects of the ecology of this particular group of extinct South American megamammals.

Dental calculus, or tartar, is a mineralized biofilm that develops on the teeth, and is often observed on the teeth of the South American proboscidean Notiomastodon platensis. This structure can provide details on paleoecological, paleoenvironmental and paleopathological aspects of a species. However, characterization of tartar in N. platensis is lacking. The aim of this study was to provide a macromorphological characterization of tartar on N. platensis molars, and evaluate its prevalence, distribution patterns and severity. A total of 117 molariforms from Brazilian Quaternary fossiliferous assemblages were analyzed. Thirty-five (29.9%) molars presented tartar. The majority displayed moderate severity. Calculus was present at least on one inteloph(id) of each molar, and prevailed on the posterior region. It predominated on lower and third molars. Adult individuals showed a predominance compared to juveniles. These patterns in N. platensis are probably due to the susceptible oral environment, molar morphology, mature age and tooth replacement. These results suggest that N. platensis and probably other proboscideans were relatively susceptible to tartar development.

The Last Glacial Maximum (LGM; 26,000–19,000 years before the present) altered the distribution of species worldwide. Its effect is poorly known in tropical regions because the cooling and drought reached during that period are uncertain. Here, I generated hypotheses regarding the possible responses of cloud forest mammals in the Oaxacan Highlands (OH) of Mexico, a region with one of the most extensive cloud forests in the Neotropics. First, I used three General Circulation Models (GCMs: CCSM3, MIROC-ESM and MPI) to characterize probable climates during the LGM. Then, I used ecological niche models to estimate the current and LGM potential distributions of four cloud forest species. As in other locations, the results show that GCMs are consistent with cooler conditions relative to today; however, the three GCMs estimate precipitation regimes with notable variations in the region. MPI indicates that the LGM could have been even wetter than present. Consequently, the MPI scenario allowed more widespread potential distributions of mammals. The paleodistributions show how mid- and lowlands were essential for the long-term survival of these ‘high-mountain mammals’ throughout the last glacial–interglacial cycle. The paleodistributions presented here are precise hypotheses that can be tested based on paleoecological and genetic evidence.

Overflow events are important embodiments of the evolutionary characteristics of the lower Yellow River. Lakes in the lower reaches of the Yellow River have the capacity to record these events. Due to the complex provenance and transport pathways of sediments in local lakes, it is difficult to extract reliable information on sediments delivered by the Yellow River based on conventional methods and proxies. Here, we show results from a genetically meaningful end-member (EM) decomposition of sediment grain-size data from Huangdun ancient lake. The grain-size of the sediments can be decomposed into three end-members. Comprehensive analysis combining environmental magnetism and geochemical indicators clarifies the significance of each end-member. EM1 represents mixed signals of various proximal fluvial sediments and the Yellow River materials. EM2 is similar to terrestrial fine-grained debris in conjunction with local pedogenic materials, aeolian inputs and some Yi River materials. EM3 represents a component that is mainly derived from long-distance transport by the lower Yellow River. End-member analysis successfully identified overflow events of the lower Yellow River on a southward-flowing path during the Holocene. This study provides a meaningful attempt to reconstruct the evolutionary history of the lower Yellow River from sedimentary records.