嘉宾（Guest）： 张弛博士 (Dr. Zhang Chi) 

讨论主题（Topic）：Bayesian tip dating reveals heterogeneous morphological clocks in Mesozoic birds 

时间（Time）： 2018年11月30日星期五 下午 3:00-4:00 

地点（Location）：古脊椎所9层报告厅（北京科技大厦） 

内容简介：Recently, comprehensive morphological datasets including nearly all the well-recognized Mesozoic birds became available, making it feasible for statistically rigorous methods to unveil finer evolutionary patterns during early avian evolution. Here, we exploited the advantage of Bayesian tip dating under relaxed morphological clocks to infer both the divergence times and evolutionary rates while accounting for their uncertainties. We further subdivided the characters into six body regions (i.e., skull, axial skeleton, pectoral girdle and sternum, forelimb, pelvic girdle, and hindlimb) to assess evolutionary rate heterogeneity both along the lineages and across partitions. We observed extremely high rates of morphological character changes during early avian evolution and the clock rates are quite heterogeneous among the six regions. The branch subtending Pygostylia shows extremely high rate in the axial skeleton, while the branches subtending Ornithothoraces and Enantiornithes show very high rates in the pectoral girdle and sternum, and moderately high rates in the forelimb. The extensive modifications in these body regions largely correspond to refinement of the flight capability. This study reveals the power and flexibility of Bayesian tip dating implemented in MrBayes to investigate evolutionary dynamics in deep time.