Testing the impact of calibration on molecular divergence times using a fossil-rich group: the case of Nothofagus (Fagales)

Although temporal calibration is widely recognized as critical for obtaining accurate divergence-time estimates using molecular dating methods, few studies have evaluated the variation resulting from different calibration strategies. Depending on the information available, researchers have often used primary calibrations from the fossil record or secondary calibrations from previous molecular dating studies. In analyses of flowering plants, primary calibration data can be obtained from macro- and mesofossils (e.g., leaves, flowers, and fruits) or microfossils (e.g., pollen). Fossil data can vary substantially in accuracy and precision, presenting a difficult choice when selecting appropriate calibrations. Here, we test the impact of eight plausible calibration scenarios for Nothofagus (Nothofagaceae, Fagales), a plant genus with a particularly rich and well-studied fossil record. To do so, we reviewed the phylogenetic placement and geochronology of 38 fossil taxa of Nothofagus and other...

尽管时间校准（temporal calibration）被广泛认为是利用分子定年方法（molecular dating methods）获取准确分化时间估计值（divergence-time estimates）的核心环节，但目前鲜有研究对不同校准策略引发的结果差异展开评估。依据可获取的资料，研究者常选用两类校准方案：一类是来自化石记录的初级校准（primary calibrations），另一类则是源自既往分子定年研究的次级校准（secondary calibrations）。在显花植物（flowering plants）类群的相关分析中，初级校准数据可来源于大化石与中化石（macro- and mesofossils，例如叶片、花与果实）或微化石（microfossils，例如花粉）。化石数据的准确性与精确性存在显著差异，这使得研究者在遴选合适的校准方案时面临艰难抉择。本研究针对化石记录极为丰富且研究充分的假山毛榉属（Nothofagus，假山毛榉科Nothofagaceae，壳斗目Fagales）这一植物类群，检验八种合理校准场景（calibration scenarios）所带来的影响。为此，我们梳理了38个假山毛榉属及其他类群的化石类群（fossil taxa）的系统发育定位（phylogenetic placement）与地质年代学（geochronology）信息……