Leaf and infructescence fossils of Alnus (Betulaceae) from the late Eocene of the southeastern Qinghai–Tibetan Plateau

Abstract

Plant fossils from the Qinghai–Tibetan Plateau (QTP), China are critical to understand not only the diversification history of plants there, but also the paleoenvironmental conditions. Alnus are deciduous trees, mainly distributed in temperate and subtropical regions of Eurasia and North America, and they are well known in the fossil records throughout the Cenozoic in the Northern Hemisphere. We collected numerous well‐preserved Alnus leaf and infructescence fossils from the Lawula Formation (∼34.6 Ma with 40Ar/39Ar dating) at the present elevation of 3910 m a.s.l. in the southeastern QTP. Based on detailed morphological comparisons with existing and fossil species, these fossils show closest affinity to Alnus ferdinandi‐coburgii C. K. Schneid., and we refer to these fossils as A. cf. ferdinandi‐coburgii. These specimens comprise the oldest megafossil record of Alnus in the QTP, and provide solid evidence for the distribution of Alnus there as early as the late Eocene. Extant A. ferdinandi‐coburgii is distributed in areas with mean annual temperature values between 9.7 °C and 16.9 °C, and mean annual precipitation values ranging from 896.2 mm to 1161.2 mm; therefore, fossils of A. cf. ferdinandi‐coburgii suggest a much warmer and wetter climate during the late Eocene than today in the southeastern QTP. This finding is consistent with other evidence for continued uplift of the southeastern QTP after the late Eocene that might be due to the eastward extension of the QTP.

Plant diversity and ecology on the Qinghai–Tibet Plateau

“…These genera showed the widespread floristic connections with Northern America and Europe in their historical distributions. These findings and those reported before (Jia et al, 2019; Xu et al, 2019; Tang et al, 2019; Su et al, 2021) suggest that some subregions of the QTP were still at relatively low altitudes at these stages compared with the present high altitudes. Therefore, the total QTP might have never been uplifted together to a high elevation at a certain stage and each subregion was subjected to different uplifts at different stages (Mao et al, 2021).…”

Evolution of Rosaceae Plastomes Highlights Unique Cerasus Diversification and Independent Origins of Fruiting Cherry

“…Therefore, we inferred that the discordance and lack of phylogeographic signals might have resulted from potential multiple hybridization events within Cerasus. Molecular dating in this study indicated that the four major groups (A I1 -A I4 ) diverged in the Middle and Late Miocene [5.96 (95% HPD: 3.06-9.73) -9.51 (95% HPD: 5.64-14.53) Mya], a period consistent with remarkable topographic changes and climatic shifts resulting from the rapid uplift of Qinghai-Tibetan Plateau (QTP) and Himalaya-Hengduan Mountains (HHM) (Favre et al, 2015;Xu et al, 2018). Under this scenario, the long-term topographic changes and climatic shifts in QTP and HHM may have promoted the potential genomic introgressions among Cerasus taxa.…”

Evolutionary origin of species diversity on the Qinghai–Tibet Plateau

“…Early Oligocene (ca. ∼34.6 Ma) Alnus found in south‐eastern margin of Tibet (Xu et al, 2019b); 6. Late Miocene (ca.…”