Steppe development and mammalian adaptation in the middle Miocene, North Junggar Basin, Central Asia

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The Central Asian (CA) steppe ecosystem and its fauna experienced a marked transition during the Miocene Climatic Optimum (MCO), though the exact process and dynamics remain elusive. We selected the Duolebulejin (DLB) section within the Junggar Basin to reconstruct vegetation and climate changes, using proxies such as particle size, mammalian fossils, and previously reported data including pollen, δ13CTOC, and magnetic susceptibility. The results reveal three distinct phases of transformation in regional vegetation and fauna from 18.8 to 13.2 Ma. During the pre-MCO (18.8–17.0 Ma), the landscape was dominated by desert scrubland, primarily inhabited by rodents. The MCO (17.0–14.5 Ma) saw a shift towards steppe vegetation, initially with herbaceous taxa followed by the establishment of C4 plants, alongside a diversity of large mammals adapted to open habitats. This suggests the emergence of savanna-like woodland steppes. In the post-MCO (14.5–13.2 Ma), the region transitioned to a dry steppe, with diminished animal populations, although a continued high proportion of species adapted to steppe environments. These findings underscore a co-evolutionary relationship between the development of steppe ecosystems and mammalian adaptations, driven by global MCO warming and subsequent cooling and with regional hydroclimatic changes acting as a modulating factor. The steppe-fauna biome emerged in the Junggar Basin during the MCO warming, a development whose mechanisms resemble those of tropical savannas in the late Miocene. These insights enhance our understanding of early steppe ecosystem evolution through past warming periods, shedding light on the pathways to modern steppe formation.