Multifaceted disparity approach reveals dinosaur herbivory flourished before the end-Cretaceous mass extinction

Understanding temporal patterns in biodiversity is an enduring question in paleontology. Compared to studies of taxonomic diversity, long-term perspectives on ecological diversity are rare, particularly in terrestrial systems. Yet ecological diversity is critical for the maintenance of biodiversity, particularly during times of major perturbations. Here, we explore the ecological diversity of Cretaceous herbivorous dinosaurs leading up to the K-Pg extinction, using dental and jaw morphological disparity as a proxy. We test the hypothesis that a decline in ecological diversity could have facilitated their rapid extinction 66 mya. We apply three disparity metrics that together capture different aspects of morphospace occupation, and show how this approach is key to understanding patterns of morphological evolution. We find no evidence of declining disparity in herbivorous dinosaurs as a whole – suggesting that dinosaur ecological diversity remained high during the last 10 million years of their existence. Clades show different disparity trends through the Cretaceous, but none except sauropods exhibits a long-term decline. Herbivorous dinosaurs show two disparity peaks characterised by different processes; in the Early Cretaceous by expansion in morphospace and in the Campanian by morphospace packing. These trends were only revealed by using a combination of disparity metrics, demonstrating how this approach can offer novel insights into macroevolutionary processes underlying patterns of disparity and ecological diversity.

解析生物多样性的时间分布模式，是古生物学领域一项经久不衰的研究课题。相较于分类多样性相关研究，针对生态多样性的长期系统性研究较为稀缺，在陆地生态系统中尤为如此。然而生态多样性对于维持生物多样性至关重要，在遭遇重大扰动的时期更是如此。本研究以牙齿与颌骨形态差异度作为替代指标，探究白垩纪植食性恐龙在白垩纪-古近纪（K-Pg）灭绝事件前的生态多样性特征。我们验证了如下假说：生态多样性的衰退或许曾加速这群恐龙在6600万年前的快速灭绝。我们采用三种差异度指标，从不同维度共同刻画形态空间占据格局，并阐明该方法对于解析形态演化模式的关键意义。我们未发现整体植食性恐龙的形态差异度出现下降的证据——这表明在恐龙存续的最后1000万年里，其生态多样性始终维持在较高水平。不同演化支在白垩纪期间的形态差异度变化趋势各不相同，但除蜥脚类恐龙外，其余类群均未出现长期的差异度衰退。植食性恐龙存在两个形态差异度峰值，其形成机制各不相同：早白垩世的峰值源于形态空间的扩张，坎潘期的峰值则源于形态空间的填充。唯有结合多种差异度指标方能揭示上述变化趋势，这也证明该方法可为解析形态差异度与生态多样性模式背后的宏观演化过程提供全新视角。