The timing of mammalian diversification in relation to the Cretaceous-Paleogene (KPg) mass extinction continues to be a subject of substantial debate. Previous studies have either focused on limited taxonomic samples with available whole-genome data or relied on short sequence alignments coupled with extensive species samples. In the present study, we improved an existing dataset from the landmark study of Meredith et al. (2011) by filling in missing fragments and further generated another dataset containing 120 taxa and 98 exonic markers. Using these two datasets, we then constructed phylogenies for extant mammalian families, providing improved resolution of many conflicting relationships. Moreover, the timetrees generated, which were calibrated using appropriate molecular clock models and multiple fossil records, indicated that the interordinal diversification of placental mammals initiated before the Late Cretaceous period. Additionally, intraordinal diversification of both extant placental and marsupial lineages accelerated after the KPg boundary, supporting the hypothesis that the availability of numerous vacant ecological niches subsequent to the mass extinction event facilitated rapid diversification. Thus, our results support a scenario of placental radiation characterized by both basal cladogenesis and active interordinal divergences spanning from the Late Cretaceous into the Paleogene.
哺乳动物的多样性形成时间与白垩纪-古近纪（KPg）大灭绝之间的关系仍然存在巨大争议。为解决这一争议，前期研究大都利用具有全基因组序列的少数物种代表类群，抑或是基于短片段序列的大范围类群取样。在该研究中,我们新产生了两个哺乳动物代表类群的核苷酸数据集，首先通过填充缺失的序列改进了Meredith 等（2011）的数据集，同时通过序列扩展和生物信息分析生成了一份包括98个编码基因外显子标记120个分类单元取样的数据集。然后，基于新构建的两个数据集，我们运用多种系统发育重建的方法构建的现生哺乳动物科级阶元的系统发育树，解决了诸多系统发育关系的冲突。进一步结合分子钟模型和化石记录矫正估计的分化时间表明，胎盘动物的目级阶元多样性始于晚白垩纪之前，而现存胎盘和有袋哺乳动物的目级阶元多样性分化发生在白垩纪-古新世（KPg）边界之后，这支持了KPg大灭绝之后存在的空余生态位促进了哺乳动物的目级阶元多样性。我们的结果暗示了一种新型的胎盘哺乳动物辐射性演化模型，其初始分化和目级阶元多样性形成从晚白垩纪持续到古新世。.
Keywords: Diversification; Evolutionary model; Mammals; Phylogeny.