Study On Samara Fossils With A Single Extended Wing From The Miocene Of Lincang, Yunnan

Yunnan Province is located in the southwestern border of China, which has a complex terrain, a varied climate and a great variety of plant and animal species. It is an ideal place to study the diversity, the evolution and the migration routes of a certain plant genera. The characteristics of reproductive organs (flowers, fruits and seeds) in angiosperm form the basis of phylogeny and systematics. The samara of Fraxinus possess a symmetrical single wing arising from the seed coat, which is the unique characteristic of this genus. The genus Fraxinus well represented in the fossil record of the Northern Hemisphere. In this study, Fraxinus cf. honshuensis and Fraxinus sp. are distinguished from another co-occured samara fossil species, Ventilago sp. and then they are described mainly based on the morphology. Furthermore, morphological characteristics of Fraxinus samara are measured both of the 12 fossil species and 9 extent species in order to obtain the evolutionary trend of the winged-fruit through the geologic time and the influence of the wind dispersal on the morphological variation of the winged-fruit in this genus. The results suggested that during Late Oligocene to Middle Miocene Fraxinus samara reached the maximum capability for wind dispersal, which is in accordance with the fossil record. The macrofossil record of this genus was firstly reported in the Eocene. The distribution based on macrofossils of this genus hadn't covered the distribution range of extent species until the Middle Miocene, confined in the North Temperate Zone across North America and Eurasia. Marcofossil records indicated that plant species of this genus migrated from the higher latitudes to the lower latitudes through the Beringia and North Atlantic Bridge before Middle Miocene and finally spread to the subtropical and tropical zone of today.