Seed cones of Picea from the early Miocene Mula Basin, Sichuan Province, southwestern China and its biogeographical implication

Picea is widely distributed in the Hengduan Mountains of southwestern China nowadays, but its megafossil records there are still rare, which prevents a full understanding of the evolutionary history of Picea in this region. In this study, we describe well-preserved fossil seed cones of Picea from the early Miocene Mula Basin in Litang County, central Hengduan Mountains. These fossil seed cones are characterized by oblong or ovate seed cones, broadly obovate seed scales with bifid apices, longitudinal striations on their abaxial surfaces, and triangular-spathulate bracts. Detailed morphological comparisons allowed us to identify these specimens as Picea sp. (cf. P. asperata). This finding implies that the ancestor of modern species for Picea in the Hengduan Mountains might have survived there by the early Miocene, much earlier than molecular phylogenetic estimates that placed their divergence there during the Pliocene. Combined with previously discovered fossil species from the same sediment, the Mula flora represents a subalpine coniferous forest, which is similar to modern vegetation nearby. It suggests that the central Hengduan Mountains were warmer and more humid during the early Miocene than today, in agreement with the global climate condition at that time.