Placental mammal diversification and the Cretaceous-Tertiary boundary
Placental mammal diversification and the Cretaceous-Tertiary boundary
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DOI：
10.1073/pnas.0334222100
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发表时间：
2003-02-04
影响因子：
11.1
通讯作者：
O'Brien, SJ
中科院分区：
文献类型：
--
作者：
Springer, MS;Murphy, WJ;O'Brien, SJ
关于胎盘哺乳动物辐射时间的竞争性假设集中在现存的胎盘目是在白垩纪-第三纪（K/T）界线之前还是之后起源和多样化的。解决这一问题的分子研究存在校准点单一、分子钟假设不可靠和/或分类群采样缺乏所有胎盘目的代表等问题。我们使用最大的胎盘哺乳动物分子数据集来研究这个问题，其中包括所有现存胎盘目代表的19个核基因和3个线粒体基因片段。我们使用了Thorne/Kishino方法，该方法允许同时从化石记录中得到约束，并允许分子进化速率在系统发育树的不同分支上变化。利用不同的化石约束条件、不同的胎盘基底先验和不同的数据分区进行的分析均支持白垩纪的序间分化，而序内分化主要发生在K/T界线之后。四个胎盘目显示出早于K/T界线的序内多样化，但平均只有1000万年。与一些分子研究将大鼠和小鼠的分裂时间定在4600万年前相比，我们的研究结果与化石记录的一致性有所提高，并将这种分裂时间定在1600万至2300万年前。为了验证白垩纪分化时间的分子估计是K/T边界后身体尺寸增加的伪产物这一假设，我们还对“K/T身体尺寸”分类群进行了分析。在这些分析中，白垩纪的间断性分裂仍然存在。
Competing hypotheses for the timing of the placental mammal radiation focus on whether extant placental orders originated and diversified before or after the Cretaceous-Tertiary (K/T) boundary. Molecular studies that have addressed this issue suffer from single calibration points, unwarranted assumptions about the molecular clock, and/or taxon sampling that lacks representatives of all placental tal orders. We investigated this problem using the largest available molecular data set for placental mammals, which includes segments of 19 nuclear and three mitochondrial genes for representatives of all extant placental orders. We used the Thorne/Kishino method, which permits simultaneous constraints from the fossil record and allows rates of molecular evolution to vary on different branches of a phylogenetic tree. Analyses that used different sets of fossil constraints , different priors for the base of Placentalia, and different data partitions all support interordinal divergences in the Cretaceous followed by intraordinal diversification mostly after the K/T boundary. Four placental orders show intraordinal diversification that pre-dates the K/T boundary, but only by an average of 10 million years. In contrast to some molecular studies that date the rat-mouse split as old as 46 million years, our results show improved agreement with the fossil record and place this split at 16-23 million years. To test the hypothesis that molecular estimates of Cretaceous divergence times are an artifact of increased body size subsequent to the K/T boundary, we also performed analyses with a "K/T body size" taxon set. In these analyses, interordinal splits remained in the Cretaceous.