Northern Hemisphere megafossil of Dacrycarpus (Podocarpaceae) from the Miocene of South China and its evolutionary and paleoecological implications

摘要

The modern genus Dacrycarpus (Endl.) de Laub.of the family Podocarpaceae,containing nine species,is mainly distributed in tropical mountain rainforests of the southwestern Pacific region,ranging from New Zealand to low-latitude Asia.This genus has abundant fossil records in both hemispheres,but all the known megafossils were limited to Australasia and South America.Here we report on Dacrycarpus guipingensis sp.nov.from the Miocene Erzitang Formation of Guangxi,South China.This is the first megafossil of Dacrycarpus in the Northern Hemisphere.The new species is represented by mummified dimorphic foliage,ovuliferous shoots,and a male cone with in situ pollen.It resembles the extant Dacrycarpus imbricatus (Blume) de Laub.,which is common in rainforests from southern China and northern Myanmar to Fiji.This paper presents the first data on the anatomical structure of seed cone and exine ultrastructure of Dacrycarpus in situ pollen grains from a fossil material by using computed tomography scanning and ultrathin sectioning.For comparative purpose,data on the pollen morphology and ultrastructure were obtained for modern D.imbricatus for the first time.The D.guipingensis fossils strongly suggest the Miocene arrival of Dacrycarpus in Asia from the Southern Hemisphere.Based on the modern ecological niche and related fossil elements,this fossil locality was probably covered by conifer-broad-leaved mountain rainforests during the Miocene.