Tavaré Simon, Marshall Charles R, Will Oliver, Soligo Christophe, Martin Robert D
Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-1340, USA.
Nature. 2002 Apr 18;416(6882):726-9. doi: 10.1038/416726a.
Divergence times estimated from molecular data often considerably predate the earliest known fossil representatives of the groups studied. For the order Primates, molecular data calibrated with various external fossil dates uniformly suggest a mid-Cretaceous divergence from other placental mammals, some 90 million years (Myr) ago, whereas the oldest known fossil primates are from the basal Eocene epoch (54-55 Myr ago). The common ancestor of primates should be earlier than the oldest known fossils, but adequate quantification is needed to interpret possible discrepancies between molecular and palaeontological estimates. Here we present a new statistical method, based on an estimate of species preservation derived from a model of the diversification pattern, that suggests a Cretaceous last common ancestor of primates, approximately 81.5 Myr ago, close to the initial divergence time inferred from molecular data. It also suggests that no more than 7% of all primate species that have ever existed are known from fossils. The approach unites all the available palaeontological methods of timing evolutionary events: the fossil record, extant species and clade diversification models.
从分子数据估算出的分歧时间往往比所研究类群已知最早的化石代表早得多。对于灵长目动物而言，用各种外部化石日期校准的分子数据一致表明，大约在9000万年前的白垩纪中期，灵长目动物与其他胎盘哺乳动物出现分歧，而已知最古老的灵长类化石来自始新世早期（5400 - 5500万年前）。灵长类动物的共同祖先应该早于已知最古老的化石，但需要进行充分的量化，以解释分子估计和古生物学估计之间可能存在的差异。在这里，我们提出了一种新的统计方法，该方法基于从物种多样化模式模型得出的物种保存估计，表明灵长类动物的白垩纪最后共同祖先大约在8150万年前，接近从分子数据推断出的初始分歧时间。它还表明，所有曾经存在过的灵长类物种中，已知化石的比例不超过7%。该方法整合了所有用于确定进化事件时间的现有古生物学方法：化石记录、现存物种和分支多样化模型。
