"寒武纪爆发"事件及其成因述评

主要后生动物门类化石在寒武纪初期的突然出现记录了生命史中一个从未有过的快速演化时期,这一事件被称为“寒武纪爆发(Cambrian explosion)”．多年来有关“寒武纪爆发”成因的各种猜测从未间断过．但是,将古生物化石记录看成是生物进化过程中种系形成的真实过程已遭到许多研究者的非议,这主要取决于以下二方面的证据：一是对早期后生动物系统发生关系的重新评估;二是来自于分子系统学和分子钟的研究．现在看来,“寒武纪爆发”事件的产生,一方面归因于化石体积的明显增加及其伴随的骨骼化过程,另一方面可能是其时的进化革新事件所导致．

THE "CAMBRIAN EXPLOSION" IN THE EVOLUTION OF METAZOA AND ITS CAUSES

The sudden appearance of the major animal phyla of metazoa in the fossil record apparently records a phase of rapid evolution at the base of the Cambrian period and this has become known as the "Cambrian explosion". This event has fuelled many speculations about its unique evolutionary mechanisms operating at that time. The acceptance of the palaeontological evidence as a true reflection of the evolutionary narrative has been criticized in two ways: from a reappraisal of the phylogenetic relationships of the early fossils of some metazoan phyla, and from predictions of molecular divergence times based on molecular clocks. The apparent paradox between the sudden appearance of recognizable metazoans and their extended evolutionary history might be explained in one way by a sudden increase in body size accompanied by skeletization, and in another way by a rapid evolutionary innovation not long before the Cambrian.