Peterson Kevin J, Cotton James A, Gehling James G, Pisani Davide
Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA.
Philos Trans R Soc Lond B Biol Sci. 2008 Apr 27;363(1496):1435-43. doi: 10.1098/rstb.2007.2233.
Unravelling the timing of the metazoan radiation is crucial for elucidating the macroevolutionary processes associated with the Cambrian explosion. Because estimates of metazoan divergence times derived from molecular clocks range from quite shallow (Ediacaran) to very deep (Mesoproterozoic), it has been difficult to ascertain whether there is concordance or quite dramatic discordance between the genetic and geological fossil records. Here, we show using a range of molecular clock methods that the major pulse of metazoan divergence times was during the Ediacaran, which is consistent with a synoptic reading of the Ediacaran macrobiota. These estimates are robust to changes in priors, and are returned with or without the inclusion of a palaeontologically derived maximal calibration point. Therefore, the two historical records of life both suggest that although the cradle of Metazoa lies in the Cryogenian, and despite the explosion of ecology that occurs in the Cambrian, it is the emergence of bilaterian taxa in the Ediacaran that sets the tempo and mode of macroevolution for the remainder of geological time.
解开后生动物辐射的时间对于阐明与寒武纪大爆发相关的宏观进化过程至关重要。由于从分子钟得出的后生动物分歧时间估计范围从相当浅（埃迪卡拉纪）到非常深（中元古代），因此很难确定遗传记录和地质化石记录之间是一致还是存在巨大差异。在这里，我们使用一系列分子钟方法表明，后生动物分歧时间的主要脉冲发生在埃迪卡拉纪，这与对埃迪卡拉纪宏观生物群的综合解读一致。这些估计对先验条件的变化具有稳健性，无论是否包含古生物学推导的最大校准点都会得出这些结果。因此，生命的两个历史记录都表明，尽管后生动物的摇篮位于成冰纪，并且尽管寒武纪出现了生态大爆发，但正是埃迪卡拉纪两侧对称类群的出现为地质历史的其余时间设定了宏观进化的节奏和模式。
