论地史上温带生物区系的识别方法

CRITERIA TOWARD RECOGNIZING MESOTHERMAL BIOTA IN GEOLOGICAL HISTORY

在地史上,热带生物区系容易识别,温带生物区系的确定则常引起争议。本文试图以现代温带生物区系的特点,应用将今论古原则,提出识别地史上温带生物区系的方法,并对一些有争议的生物区系性质提出看法。按 Strahler(1973)的 K(?)ppen-Geiger 分类,现代的温带相当于 Mesothermal 气候。它的含义是:最低月均温低于18℃,高于-3℃。

This paper proposes six criteria to help recog- nize the mesothermal biota in geological history. 1.Remarkably lower diversity than that of tropical biota.Statistics presented herein show that the ratio between both of them is 1:1.5—3(modern) and 1:2—6(past).In the geological past,a dra- stic shift-line in diversity would be a potential tropical-temperate zone boundary. 2.Bipolar distribution to the southern and northern sides of tropical biota.This criterion has been proved valid by many modern and ancient examples.In geohistory of China such bipolar distributions have been recognized to occur since Silurian and exist in all later periods.The Triassic Lystrosaurus and Kannemeyeria faunas are consid- ered as warm-temperate rather than tropical due to their bipolar distribution and their neighborhood with the Dicroidium flora of a temperate climate. 3.Low endemism and high cosmopolitanism, with few stenothermal and many eurythermal ele- ments.The low endemism percentage of the T(?)va- ella assemblage,previously considered by some authors to be merely representing an endemic cen- ter,is here interpreted as the characteristic of a temperate zone. 4.Biota inhabiting ancient temperate zones identified through paleoclimatic analysis or organic characters.In this paper,the established meso- thermal biotas in geohistory are enumerated,and the characters of mesothermal floras such as growth rings,deciduousness,relative abundance of coni- fers,ginkgopsids vs.cycadales,etc.,are also men- tioned. 5.Recognition of Mesozoic and Cenozoic mesothermal biota in China through sequential an- alysis of climate zonation.Thus,for example,the Northern-type floras of Mesozoic periods are se- lected as climatic index fossil groups for temperate zones. 6.Riddance from the effects caused by high altitude,tropical submergence,hypersalinity and other abnormal environments which may form su- perficial similarities to those of mesothermal biotas.