Data from: Multiple morphological clocks and total-evidence tip-dating in mammals

Morphological integration predicts that correlated characters will co-evolve; thus, each distinct suite of correlated characters might be expected to evolve according to a separate clock or "pacemaker". Characters in a large morphological dataset for mammals were found to be evolving according to 7 separate clocks, each distinct from the molecular clock. Total-evidence tip dating using these multiple clocks inflated divergence time estimates, but potentially improved topological inference. In particular, single-clock analyses placed several meridiungulates and condylarths in a heterodox position as stem placentals, but multi-clock analyses retrieved a more plausible and orthodox position near ungulates within crown placentals. Several shortcomings (including uneven character sampling) currently impact upon the accuracy of total-evidence dating, but this study suggests that when sufficiently large and appropriately constructed phenotypic datasets become more commonplace, multi-clock approaches are feasible and can affect both divergence dates and phylogenetic relationships.

形态整合（Morphological integration）理论预测，相关性状会发生协同演化；因此，每一组独立的相关性状集合，或许应按照各自独立的演化钟（或称“节律起搏器”）进行演化。针对哺乳动物的大型形态数据集开展的分析显示，其包含的性状共遵循7种独立的演化钟，且均有别于分子钟（molecular clock）。采用这类多演化钟方案开展总证据末端定年（total-evidence tip dating），会放大分歧时间估计值，但却有可能提升拓扑结构推断的精度。具体而言，单演化钟分析将多个南美有蹄类（meridiungulates）与踝节目类群（condylarths）置于反常的胎盘类干群（stem placentals）位置；而多演化钟分析则得到了更具合理性且符合经典认知的结果，即将其归入冠群胎盘类（crown placentals）中与有蹄类（ungulates）相近的演化分支。当前仍存在若干局限性（包括性状采样不均），会对总证据定年的准确性造成影响，但本研究表明，当足够大型且构建合理的表型数据集愈发普及时，多演化钟方法具备可行性，且可同时对分歧时间与系统发育关系（phylogenetic relationships）产生影响。