Zhang Chi, Wang Min
Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, People's Republic of China.
Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Beijing 100044, People's Republic of China.
R Soc Open Sci. 2019 Jul 24;6(7):182062. doi: 10.1098/rsos.182062. eCollection 2019 Jul.
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 estimate 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 an extremely high rate in the axial skeleton, while the branches subtending Ornithothoraces and Enantiornithes show notably 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.
最近，包含几乎所有已被广泛认可的中生代鸟类的综合形态学数据集已经可得，这使得运用统计严格的方法揭示早期鸟类进化过程中更精细的进化模式成为可能。在此，我们利用宽松形态钟下贝叶斯末端定年法的优势，在考虑分歧时间和进化速率不确定性的同时对二者进行估计。我们进一步将特征细分为六个身体区域（即头骨、中轴骨骼、肩带和胸骨、前肢、腰带和后肢），以评估沿谱系和跨分区的进化速率异质性。我们观察到在早期鸟类进化过程中形态特征变化速率极高，且六个区域的时钟速率差异很大。尾综骨分支在中轴骨骼上显示出极高的速率，而鸟胸类和反鸟类分支在肩带和胸骨上显示出显著高的速率，在前肢上显示出中等高的速率。这些身体区域的广泛变化在很大程度上与飞行能力的优化相对应。本研究揭示了在MrBayes中实施的贝叶斯末端定年法在研究深层时间进化动态方面的强大功能和灵活性。
