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In this paper, we report late Pleistocene to Holocene changes in the shell size and age structure of the gastropod, Opeas striatissimum, in two loess profiles in the Chinese Loess Plateau, spanning the past 27 ka. During the interval of ~17–8 ka, in response to climatic warming, we observed marked increases in shell dimensions and a more diverse age structure (age classes), as well as a ~20% increase in the number of adult individuals. Shell growth and enhanced survival from juvenile to adult, in turn, resulted in an increase in the population size, which reached a maximum during the interval ~8–3 ka, corresponding to the Holocene Climatic Optimum. We also observed an abrupt decrease in shell height and related significant decreases in the total number of individuals of Opeas striatissimum and adult individuals at the time of the Younger Dryas cold climatic event. We suggest that the observed morphologic and demographic changes observed for Opeas striatissimum reflect changes in the growing season, linked to changes in monsoon rainfall and climate stability, in response to climate fluctuations from the late Pleistocene to the Holocene. Our study provides a long-term perspective that helps refine mechanistic population models of invertebrates in the face of future climate change.

A new molluscan fossil record from the late Miocene–Pliocene Xifeng Red Clay sequence in the central Loess Plateau, northern China, reveals the process of ecological environmental changes during ∼ 6.2–2.4 Ma. Three marked ecological shifts in mollusk assemblages occurred at about 5.4, 4.5, and 3.4 Ma, which reflect changes in the East Asian monsoon circulation. A predominantly cold-aridiphilous group reveals an extremely cold dry climate due to strengthened East Asian winter monsoon during ∼ 6.2–5.4 Ma. A predominantly thermo-humidiphilous group from ∼ 5.4–4.5 Ma indicates a strengthening of the East Asia summer monsoon circulation. The marked occurrence of meso-xerophilous taxa during ∼ 4.5–3.4 Ma implies mild climatic conditions. From 3.4 Ma, the cold-aridiphilious species again became dominant in the fossil assemblages, indicating that the winter monsoon was gradually intensifying towards the Quaternary glaciations. Climate changes in this region were characterized by stepwise cooling from 5.4 to 2.4 Ma with a 1 Ma rhythmicity. The cooling trend is in good agreement with the general global cooling trend during this period, as documented by marine δ18O records. The formation and development of the Northern Hemisphere ice sheets during the late Pliocene accelerated the climate deterioration towards the Quaternary glaciations. The history of environmental changes revealed by the Red Clay molluscan fossils is coupled in phase with the process of Tibetan Plateau uplift, which may be the major cause and forcing mechanism of late Miocene–Pliocene environmental changes in the Loess Plateau.