Cones and leaves of Tsuga from the Lower Miocene of Inner Mongolia and their paleoclimate implications
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Abstract:
Tsuga Carr. is a genus of evergreen trees in Pinaceae, with disjunct distributions in warm, humid ecosystems between East Asia and North America. In this study, we describe three cones and two leaves of Tsuga collected from the Lower Miocene Hannuoba Formation in Zhuozi County, central Inner Mongolia, China. This report represents the first time that these two organs of Tsuga have been found from the same geological horizon and locality. The morphology of the three-dimensionally preserved cones was examined using Micro-CT scanning, while the microstructures of the leaves were studied via cuticle analysis. Through detailed comparisons with extant Tsuga species and other related fossil taxa, these three cone specimens are assigned to a new species, Tsuga zhuoziensis sp. nov., and the two leaves are assigned to Tsuga cf. T. dumosa. Morphologically, the new species is most similar to extant Tsuga dumosa, suggesting a close phylogenetic relationship. Based on the climate preferences of Tsuga dumosa and the climate data of previously reported Early Miocene fossil relatives from Zhuozi, it is inferred that the mean annual temperature during the Early Miocene in this region was approximately 6–10℃ higher than that of today, with annual precipitation exceeding 700 mm. This indicates that the Early Miocene paleoclimate of Zhuozi was significantly warmer and wetter than that of the present. In conjunction with Tsuga fossils from the Early Miocene of Weichang, Hebei Province, this study further supports the inference that North China experienced a warmer and more humid climate during the Early Miocene than today.
