Tao Jun-Rong, Xiong Xian-Zheng
1986, 24 (2): 121–135
The present paper deals with a collection of plant fossils from the Wuyun Group of Heilongjiang Province. These fossils belong to 28 families, 39 genera
and 53 species. The flora is composed of 7 species of pteridophytes, 8 of conifers and 37
of 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 of
them are temperate ones. The flora consists of conifers and broad-leaved trees adapted
to humid warm-temperate or subtropic climate.
With the physiognomy of leaves, 40 per cent of them are of entire margin, and most
are medium-sized, with some megaphyllous. The nervation is mostly palmate. These
characters indicate that the climate was warm-temperate or subtropic.
Among 35 genera known from the Late Cretaceous of East Asia, 27 are also found
in North America, which indicates that the floristic relationship between East Asia and
North Americal was closer at that time than it is now. Therefore the number of
genera in common has been decreasing through the age, because these two regions have
been 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 both
continents. After the early Tertiary the floras of East Asia and North America have
been developing independently.
The Chinese flora of the Late Cretaceous may be divided into three Zones from the
north to the south: (1) warm temperate-subtropic zone, rich in Metasequoia, Ginkgo,
Trochodendroides, Platanus, Trochodendron, Protophyllum, Ampelopsis Pterospermites
and Menispermites; (2) subtropic or dry subtropic transitional zone; and (3) subtropictropic zone, rich in Brachyphyllum, Cinnamomum, Nectandra and Palms.
The Wuyun flora is considered closely related to the Chajiayang Group and SikhoteAlin flora of USSR, with 15 genera in common and also related to the Kuji flora of
Japan (Cenonian), with 11 genera in common. It is interesting to note that 11 genera
are also found in North America (Canada and Alaska) of the Late Cretaceous. The palynological assemblage of the Wuyun flora is closely related to Minshui flora of the Souliao Basin, 15 genera being common to the both. Seventy per cent of megafossils of
the Wuyun flora have become extinct, which seems to show that the age of the flora is
older than Paleocene and is assigned to the Latest Late Crataceous (Maestrichtian-Dani-an).