Data from: Eutherian morphological disparity across the end-Cretaceous mass extinction

In the aftermaths of mass extinction events, during radiations of clades, and in several other evolutionary scenarios, there is often a decoupling of taxonomic diversity and morphological disparity. The placental mammal radiation after the end-Cretaceous mass extinction is one of the archetypal adaptive radiations, but the change in morphological disparity of the entire skeleton has never been quantified across this important boundary. We reconstruct ancestral morphologies of 680 discrete morphological characters onto dated phylogenies of 177 mostly Cretaceous and Palaeogene eutherians (placental mammals and their stem relatives). Using a new approach to incorporate morphologies representing ghost lineages, we assess three measures of morphological disparity (sum of ranges, sum of variances and mean pairwise dissimilarity) across stage-level time bins within the Cretaceous and Palaeogene. We find that the range-based metric suggests that eutherian disparity increased immediately after the end-Cretaceous mass extinction, while both variance-based metrics declined from the Campanian to the Maastrichtian, but showed no change in disparity from the Maastrichtian to the Puercan – the first North American Land Mammal Age of the Paleocene. Increases in variance-based metrics lag behind the range-based metric and per-lineage accumulation rate, suggesting that the response of mammals to the Cretaceous–Palaeogene event was characterized by an early radiation that increased overall morphospace occupation, followed later by specialization that resulted in increased dissimilarity.

在大灭绝事件之后、支系辐射演化期间以及其他多种演化场景中，分类多样性（taxonomic diversity）与形态差异度（morphological disparity）时常出现解耦现象。白垩纪末期大灭绝后的胎盘哺乳动物辐射演化是典型的适应辐射之一，但学界尚未针对这一重要演化界线（白垩纪-古近纪界线）量化过整个骨骼的形态差异度变化。本研究基于177种（绝大多数为白垩纪和古近纪真兽类（eutherians，胎盘哺乳动物及其干群类群））的定年系统发育树，对680个离散形态特征开展祖先形态重建。我们采用一种纳入幽灵支系（ghost lineages）代表形态的新方法，针对白垩纪和古近纪的阶级时间间隔，评估了三种形态差异度测度指标：范围总和（sum of ranges）、方差总和（sum of variances）与平均成对差异度（mean pairwise dissimilarity）。研究结果显示，基于范围的测度指标表明，真兽类的形态差异度在白垩纪末期大灭绝后立即上升；而基于方差的两种测度指标则从坎潘期（Campanian）向马斯特里赫特期（Maastrichtian）呈下降趋势，但从马斯特里赫特期到普尔喀阶（Puercan，古近纪北美首个陆地哺乳动物年代单元）未发生显著变化。基于方差的测度指标的增长滞后于基于范围的测度指标以及每支系积累速率，这表明哺乳动物对白垩纪-古近纪灭绝事件的响应呈现出早期辐射特征：整体形态空间占据度先得到提升，随后通过特化演化导致差异度进一步升高。