黑龙江晚白垩世植物区系及东亚、北美区系的关系(续)

The Latest Cretaceous Flora of Heilongjiang Province and the Floristic Relationship Between East Asia and North America (Cont.)

The present paper deals with a collection of plant fossils from the Wu-yun Group of Heilongjiang Province.  These fossils belong to 28 families, 39 generaand 53 species.  The flora is composed of 7 species of pteridophytes, 8 of conifers and 37of angiosperms.  All have been fully described, of which ten are new species.     Most elements of this flora are subtropic or warm-temperate, with only a few ofthem are temperate ones.  The flora consists of conifers and broad-leaved trees adaptedto humid warm-temperate or subtropic climate.      With the physiognomy of leaves, 40 per cent of them are of entire margin, and mostare medium-sized, with some megaphyllous. The nervation is mostly palmate.  Thesecharacters indicate that the climate was warm-temperate or subtropic.     Among 35 genera known from the Late Cretaceous of East Asia, 27 are also foundin North America, which indicates that the floristic relationship between East Asia andNorth Americal was closer  at that time than it is now. Therefore the number ofgenera in common has been decreasing through the age, because these two regions havebeen detached from each other since the late Eocene, as a result of continental drift.Only some relic forms left on both sides, and only 4.1% of genera are common to bothcontinents.  After the early Tertiary the floras of East Asia and North America havebeen developing independently.      The Chinese flora of the Late Cretaceous may be divided into three Zones from thenorth to the south: (1) warm temperate-subtropic zone, rich in Metasequoia, Ginkgo,Trochodendroides, Platanus, Trochodendron, Protophyllum, Ampelopsis Pterospermitesand Menispermites; (2) subtropic or dry subtropic transitional zone; and (3) subtropic-tropic zone, rich in Brachyphyllum, Cinnamomum, Nectandra and Palms.      The Wuyun flora is considered closely related to the Chajiayang Group and Sikhote-Alin flora of USSR, with 15 genera in common and also related to the Kuji flora ofJapan (Cenonian), with 11 genera in common.  It is interesting to note that 11 generaare also found in North America (Canada and Alaska) of the Late Cretaceous.  The pa-lynological assemblage of the Wuyun flora is closely related to Minshui flora of the So-uliao Basin, 15 genera being common to the both.  Seventy per cent of megafossils ofthe Wuyun flora have become extinct, which seems to show that the age of the flora isolder than Paleocene and is assigned to the Latest Late Crataceous (Maestrichtian-Dani-an).