木兰科的化石记录

通过整理和分析木兰科植物的化石记录发现：不论是植物大化石还是花粉，迄今为止在白垩纪以前地层中尚无可靠的记录，自白垩纪以来，木兰科的许多种广泛发生于北半球，如亚洲，欧洲及北美等地，但非洲和大洋洲至今尚未发现木兰科的化石记录。该科最早的化石记录为中国东北延吉地区早白垩世大拉子组的喙柱始木兰Archimagnolia rostrato-stylose Tao et Zhang. 根据现有化石记录，并结合木兰科现代植物的地理分布，推测：1）木兰科的起源时间不迟于早白垩世Aptian-Albian期；2）木兰科起源地点可能是东亚，后来经过欧洲进入北美，再从北美迁移到达南美洲；3）在地质历史时期，木兰属的出现比鹅掌楸属早，从而支持根据形态学与分子系统学研究得出的木兰属较鹅掌楸属原始的结论。

FOSSIL RECORDS OF MAGNOLIACEAE

Based on the fossil records, it is found that no credible megafossil record of Magnoliaceae exists in Jurassic deposits and all Jurassic microfossil reports remain equivocal and require further study up to now. Many species of Magnoliaceae were widely distributed in the Northern Hemisphere, such as Asia, Europe and North America while there was no fossil record in Africa and Oceania since Cretaceous. Among the magnoliaceous fossils, the earliest one is Archimagnolia rostrato stylosa Tao et Zhang reported from the Lower Cretaceous Dalazi Formation of Yanji district, Northeast China. According to the fossil records and the distribution pattern of extant Magnoliaceae, the results can be drawn as follows: 1) This family originated no later than Early Cretaceous (Aptian to Albian). 2) It seems that this family probably originated in East Asia, and then spread southward to tropical Asia and northward to Europe. The North American Magnoliaceae may have been derived from the Eurasian landmass before the complete separation between North America and Europe, and the South American Magnoliaceae might come from North America. 3) The fact that Magnolia occurred earlier than Liriodendron supports the result drawn from morphological and molecular analysis that Magnolia is more primitive than Liriodendron.