New insights on angiosperm crown age based on Bayesian node dating and skyline fossilized birth-death approaches

Despite considerable work in recent years, pinpointing the time when angiosperms originated has been challenging. However, the rapid development of molecular clock methodology has provided new tools to resolve this conundrum. In particular, the fossilized birth-death model establishes a rich interplay between molecules and stratigraphy by incorporating fossils explicitly into dating analyses. In this study, we apply Bayesian node dating and the skyline fossilized birth-death model, which differ in how the calibration is applied, to estimate the crown age of angiosperms. Node dating analyses with different calibration strategies show that the posterior distribution is strongly constrained by the effective prior at the node of crown angiosperms, dominated by the maximum age constraint. Using the skyline fossilized birth-death model, we reveal that assigning different priors for origin time resulted in similar crown ages for angiosperms. Moreover, the oldest fossils play a significant role in time estimates, and the dating results are robust to sampling assumptions of extant taxa. Our dating analyses indicate a largely Triassic crown age (255–202 Ma) for angiosperms, the period when mammals, dinosaurs, and squamate reptiles first appeared, and highlight the potential of morphological data to redefine the timeline of angiosperms.尽管近年来已有大量相关研究，但精准确定被子植物（angiosperms）的起源时间仍颇具挑战。然而，分子钟方法（molecular clock methodology）的快速发展为解决这一难题提供了新的工具。其中，化石出生-死亡模型（fossilized birth-death model）通过将化石明确纳入定年分析，实现了分子数据与地层学的深度结合。本研究采用贝叶斯节点定年（Bayesian node dating）与天际线化石出生-死亡模型（skyline fossilized birth-death model）——二者在定标方式上存在差异——以估算被子植物的冠群年龄（crown age）。采用不同定标策略的节点定年分析显示，被子植物冠群节点处的后验分布（posterior distribution）受有效先验（effective prior）的强烈约束，且以最大年龄定标为主导。通过天际线化石出生-死亡模型，本研究发现，即便为起源时间设置不同的先验分布，所得被子植物冠群年龄仍较为相近。此外，最古老的化石对时间估算具有显著影响，而定年结果对现生类群（extant taxa）的采样假设具有稳健性。本研究的定年分析结果表明，被子植物的冠群年龄大致处于三叠纪（Triassic）时期（255–202 Ma），该时期也是哺乳动物、恐龙与有鳞爬行动物首次出现的阶段；本研究同时凸显了形态学数据在重新界定被子植物演化时间线方面的潜力。