Data from: Tips and nodes are complimentary not competing approaches to the calibration of molecular clocks

Molecular clock methodology provides the best means of establishing evolutionary timescales, the accuracy and precision of which remain reliant on calibration, traditionally based on fossil constraints on clade (node) ages. Tip calibration has been developed to obviate undesirable aspects of node calibration, including the need for maximum age constraints that are invariably very difficult to justify. Instead, tip calibration incorporates fossil species as dated tips alongside living relatives, potentially improving the accuracy and precision of divergence time estimates. We demonstrate that tip calibration yields node calibrations that violate fossil evidence, contributing to unjustifiably young and ancient age estimates, less precise and (presumably) accurate than conventional node calibration. However, we go on to show that node and tip calibrations are complementary, producing meaningful age estimates, with node minima enforcing realistic ages and fossil tips interacting with node calibrations to objectively define maximum age constraints on clade ages. Together, tip and node calibrations may yield evolutionary timescales that are better justified, more precise and accurate than either calibration strategy can achieve alone.分子钟方法是构建进化时间尺度的最优手段，其准确性与精确性始终依赖于定标环节。传统定标通常基于支系（节点）年龄的化石约束。末端定标（tip calibration）方法的提出，旨在规避节点定标的诸多弊端——其中包括对最大年龄约束的需求，而这类约束往往极难被证实合理。与之相反，末端定标将化石物种作为带有定年信息的末端类群，与现存近缘类群一同纳入分析，有望提升分化时间估计的准确性与精确性。本研究表明，末端定标所生成的节点定标结果会违背化石证据，导致不合理的过新或过古老的年龄估计，其精确性与（据推测）准确性均不及传统节点定标。然而，本研究进一步证实，节点定标与末端定标二者互为补充，可得到具有生物学意义的年龄估计结果：节点最小年龄约束可确保年龄估计符合实际，而化石末端类群与节点定标结合，则能客观地为支系年龄确立最大年龄约束。综上，末端定标与节点定标结合使用，可得到比单一定标策略更具合理性、精确性与准确性的进化时间尺度。