|Alternative Title||Fossil conifers from the Pliocene of Tengchong,Yunnan Province,China and their palaeobiogeographic significances|
|Place of Conferral||兰州|
|Keyword||松科 柏科 罗汉松科 上新世 腾冲 古生物地理|
松柏植物是现生最繁盛的裸子植物，种类繁多，广泛分布于不同纬度和不同海拔高度的平原、山区。由于剧烈的地壳运动和海陆变迁，为被子植物的繁盛提供了适度的湿度条件，使被子植物在晚白垩世晚期迅速兴盛，而繁盛于中生代的松柏植物逐渐被其所替代。新生代时期，气候总体呈现变冷，变干的趋势性变化，期间也经历了多次变暖变冷时期，植物分布范围随之扩张或撤退，最终形成如今的地理分布。云南省位于我国西南边陲, 由于青藏高原大规模的隆升和解体过程，使这里河川密布，峰峦叠翠，地貌结构复杂, 使其具有独特的植被景观和立体的气候特征。由于其独特的地理环境，在新生代气候变冷期间常成为植物避难所，并且在山间盆地中，地层层序发育完全，化石保存丰富，是研究新生代植物演化分布的理想场所。本文研究的松柏类化石采自云南腾冲团田盆地的上新统芒棒组，通过对叶片宏观形态以及角质层微细特征综合分析，本文共鉴定了松柏类3科4属4种化石，其中松科1种：Pinus plioarmandii为作者已正式发表新种；罗汉松科2属2种：Podocarpus cf. forrestii，Nageia cf. nagi为现生植物相似种；柏科1种：Calocedrus lantenoisii为已知化石种。
根据本文化石及之前的化石记录，推测了植物古地理：(1) 至少在晚始新世单维管束亚属(Subgen. Strobus)植物就已传播至中国南部，化石种如今在云南西部并没有分布，推测由于更新世的多次冰期，化石种从云南西部的高山区撤退至避难区，而造山运动快速抬升形成的高山以及深切的山谷，成为其在间冰期基因交流的地理障碍。(2) 罗汉松属(Podocarpus)植物广泛分布于始新世时的南半球，之后向北迁移，在始新世晚期至渐新世时已分布于北半球中高纬度地区，此后向中低纬度分化，至中新世-上新世时在中国南部已有分布。竹柏属(Nageia)植物在早白垩世时起源于东亚东北部地区，之后向南迁移，始新世时分布于中国南部，中国南部热带地区可能是其早期分化地区。此后随着气候变冷，而逐渐消失，直到中新世至上新世气候逐渐变暖而重新分布于中国南部。(3)翠柏属(Calocedrus)在北美与东亚植物区系之间亲缘关系较近，而与欧洲区系亲缘关系较远，可能是新生代时期北美与东亚植物通过白令陆桥迁移的结果，而大陆内部南北向的海道阻隔植物传播使其成为独立的植物区系。松属单维管束亚属、罗汉松属、竹柏属以及翠柏属植物指示温暖湿润的气候，并且在上新世其分布范围较现在广泛，推测腾冲上新世时期气候温暖湿润，气温可能比现在高。
Conifers are the most flourishing gymnosperms. They are widely distributed in plains and mountainous areas with different latitudes and different altitudes. Severe crustal movement and sea-land change provide a moderate humidity condition for the prosperity of angiosperms, which rapidly flourish in the Late Cretaceous, replacing the dominant position of conifers. In the Cenozoic, the climate in general showed cold and dry trend. During the period of warming and cooling, the range of plant distribution was expanded or withdrawn, and the geographical distribution was finally formed.Yunnan province is located in the southwestern frontier of China. Due to the large-scale uplift and disintegration of the Qinghai Tibet Plateau, the rivers and moutains are densely distributed. The complex geomorphology structure make it unique to the vegetation landscape and the stereoscopic climate characteristics. Because of its unique geographical environment, it often becomes a plant refuge during the cold period of the Cenozoic. And the stratigraphic sequence is fully developed and the fossil remains rich in the inter mountain basin, which is an ideal place to study the evolution and distribution of the Cenozoic plants.
The coniferous fossils studied in this paper are collected from the Mangbang Formation in the Tuantian Basin, Tengchong, Yunnan, which is assigned to the Pliocene. 4 species of 4 genera within 3 families are identified, based on comprehensive analysis of leaf macromorphology and cuticle characteristics, including a new species-Pinus plioarmandii, two sibling species of extant plants, Podocarpus cf. forrestii and Nageia cf. nagi, one Known fossil species, Calocedrus lantenoisii.
Based on the coniferous fossils studied in this paper and previous fossil record, we have deduced the palaeobiogeography. (1) The fossil record indicated that the white pines had migrated to southern China by at least the Late Eocene. However, Asian white pines do not occur in or adjacent to our fossil site in western Yunnan today. Therefore, we consider that the glacial events during the Pleistocene are the possible factors for white pines to retreat from western Yunnan, and the rapidly uplifted mountains and deep river valleys might have posed a significant geographic barrier for the genetic exchange during the warm interglacials. (2) The genus Podocarpus distributed in the Southern Hemisphere during Eocene, then moved northward. It was distributed in the mid-high latitudes of the Northern Hemisphere during the Late Eocene to Oligocene. Afterwards, it dispersed to the low and intermediate latitude areas, it distributed in the southern China during the Miocene-Pliocene. Nageia might originated in the northeastern part of Asia in the Early Cretaceous and dispersed to South China at least in the Eocene, which may be one fo the centers for early diversiﬁcation of Nageia. They gradually disappeared until the climate became warmer during the Miocene-Pliocene and redistributed in the southern China, as the climate became cold. (3) The same as the Pinus, Calocedrus North America flora has close relationship with East Asian flora, but has a distant relationship with European flora, which may be the result of the communication between the North American flora and the East Asian flora through the Bering land bridge in the Cenozoic era, while the seaways that extended the full north-south length of the continents divided the continents into separate phytogeographic provinces.The habitat of Podocarpus, Nageia, Calocedrus, the subgenus Strobus is the warm and humid envoirment. And their distribution is larger during the Pliocene than it is today. We infer that the climate of Tengchong is warmer and more humid during the Pliocene.
|安鹏程. 云南腾冲上新世松柏类化石与古生物地理意义[D]. 兰州. 兰州大学,2018.|
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