华南奥陶纪末大灭绝后腕足动物是否存在“小型化效应”？

DOES "LILLIPUT EFFECT" OF BRACHIOPODS EXIST IN SOUTH CHINA AFTER THE LATE ORDOVICIAN MASS EXTINCTION?

小型化效应(Lilliput effect)一般是指灭绝事件后生物个体相对于事件前明显变小的一种演化现象。为了更深入研究,文中将它分为狭义与广义两种类型:狭义型是指它的原始定义,专门针对种级分类单元的小型化,因研究条件苛刻而导致相关研究很少;广义型是指高于种级分类单元的小型化,已有一些实例。文章对华南奥陶纪末大灭绝前后"Katian晚期"、"Hirnantian"及"Rhuddanian初期"3个时期的腕足动物个体大小数据,依"属"、"超科"及"目"3级分类单元有选择地进行比较。分析结果表明,奥陶纪末大灭绝后残存期里较低级分类单元(属级)在个体大小变化方面显示较大的差异性,这与二叠纪末大灭绝后普遍的小型化有很大差别,这可能是因为奥陶纪末的灭绝强度远低于后者所致;同一较高级分类单元中不同属级分子个体变化趋势表现出较为一致的现象,反映出它们可能具有相似的灾难应对机制。

In the immediate aftermath of mass extinction, organisms are typically much smaller than during pre-extinction times. This evolutionary phenomenon is named ＂Lilliput effect＂. For indepth research, the effect is divided into two types： the special type, refers to the original definition of the effect which aims at species level, but it is too strict to prove; the general type, with some cases which related to higher taxa than species level. This study compares body size of the brachiopods from South China through the Ordovi clan mass extinction （late Katian, Hirnantian, earliest Rhuddanian three time intervals） at ＂generic＂, ＂super familial＂ and ＂ordinal＂ levels. The result indicates that the body sizes of the lower taxa （generic level） are highly variable, which is different from the Lilliput effect from end Permian mass extinction because the intensity of the end Ordovielan mass extinction is much less than the latter. The consistency of the variation in some higher taxa possibly suggests that the braehiopods from the same higher taxon have similar surviving strategies.