Data from: Mammals across the K/Pg boundary in northeastern Montana, U.S.A.: dental morphology and body-size patterns reveal extinction selectivity and immigrant-fueled ecospace filling

The Cretaceous/Tertiary (K/Pg) mass extinction has long been viewed as a pivotal event in mammalian evolutionary history, in which the extinction of non-avian dinosaurs allowed mammals to rapidly expand from small-bodied, generalized insectivores to a wide array of body sizes and ecological specializations. Many studies have used global- or continental-scale taxonomic databases to analyze this event on coarse temporal scales, but few studies have documented morphological diversity of mammalian paleocommunities on fine spatiotemporal scales in order to examine ecomorphological selectivity and ecospace filling across this critical transition. Focusing on well-sampled and temporally well-constrained mammalian faunas across the K/Pg boundary in northeastern Montana, I quantified dental-shape disparity and morphospace occupancy via landmark- and semilandmark-based geometric morphometrics and mean body size, body-size disparity, and body-size structure via body-mass estimates. My results reveal several key findings: (1) latest Cretaceous mammals, particularly metatherians and multituberculates, had a greater ecomorphological diversity than is generally appreciated, occupying regions of the morphospace that are interpreted as strict carnivory, plant-dominated omnivory, and herbivory; (2) the decline in dental-shape disparity and body-size disparity across the K/Pg boundary shows a pattern of constructive extinction selectivity against larger-bodied dietary specialists, particularly strict carnivores and taxa with plant-based diets, that suggests the kill mechanism was related to depressed primary productivity rather than a globally instantaneous event; (3) the ecomorphological recovery in the earliest Paleocene was fueled by immigrants, namely three multituberculate families (taeniolabidids, microcosmodontids, eucosmodontids) and to a lesser extent archaic ungulates; and (4) despite immediate increases in the taxonomic richness of eutherians, their much-celebrated post-K/Pg ecomorphological expansion had a slower start than is generally perceived and most likely only began 400,000 to 1 million years after the extinction event.

白垩纪/古近纪（K/Pg）大灭绝长期以来被视为哺乳动物演化史上的关键转折事件，非鸟类恐龙的灭绝使得哺乳动物得以从小型泛化食虫类类群快速辐射演化，形成了多样的体型与生态特化类型。既往诸多研究多采用全球或大陆尺度的分类学数据库，在较粗的时间尺度上分析该灭绝事件，但鲜有研究通过精细的时空尺度对哺乳动物古群落的形态多样性展开系统性探究，以检验该关键过渡阶段的生态形态选择性与生态位填充模式。

本研究聚焦蒙大拿州东北部K/Pg界线附近采样充分且时间约束严谨的哺乳动物化石群，通过基于标志点与半标志点的几何形态测量学（geometric morphometrics）定量分析牙齿形态差异度与形态空间占据情况，并通过体重估算值量化平均体重、体型差异度与体型结构特征。

研究结果揭示了四项核心发现：
（1）晚白垩世哺乳动物，尤其是后兽类（Metatheria）与多瘤齿兽类（Multituberculata），其生态形态多样性远超以往学界认知，占据了被认定为严格食肉、植物主导杂食以及植食性的形态空间区域；
（2）K/Pg界线两侧的牙齿形态差异度与体型差异度均出现下降，该模式呈现出针对大体型食性特化类群的选择性灭绝特征，其中尤以严格食肉动物与植食性类群最为显著，这表明此次灭绝机制与初级生产力受抑制相关，而非全球性瞬时突发事件；
（3）古新世早期的生态形态恢复主要由迁入类群驱动，包括三个多瘤齿兽科：带纹兽科（Taeniolabididae）、微兽科（Microcosmodontidae）与真兽齿兽科（Eucosmodontidae），以及占比相对较低的古有蹄类；
（4）尽管真兽类（Eutheria）的分类丰富度在灭绝事件后即刻出现上升，但其广受赞誉的K/Pg后生态形态辐射的起始速度却远慢于以往认知，且极有可能仅在灭绝事件发生后的40万至100万年才真正启动。