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

Klara K Nordén,Thomas L Stubbs,Albert Prieto-Márquez,Michael J Benton

doi:10.1017/pab.2018.26

Abstract

AbstractUnderstanding temporal patterns in biodiversity is an enduring question in paleontology. Compared with 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, especially 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 Ma. 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 Myr 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 characterized 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.

Highlights

Studies of biodiversity in deep time are often focused on taxonomic diversity (Jackson and Johnson 2001)
There is a major discrepancy between the two distance measures in the time from the Albian to the Turonian–Coniacian, when the maximum observable distances (MORD) metric records a sharp rise, but the generalized Euclidean distances (GED) metric suggests unchanged or decreasing disparity
Disparity Trends in the Cretaceous.—We find three key results: (1) an Aptian peak in disparity characterized by expansion and packing; (2) a second disparity peak in the Campanian characterized by intense morphospace packing; and (3) a thinning out of morphospace in the Maastrichtian

Summary

Introduction

Studies of biodiversity in deep time are often focused on taxonomic diversity (Jackson and Johnson 2001). A recent study exploring both taxonomic and ecological diversity of bivalves during extinction events in the Phanerozoic found that great losses in taxonomic diversity did not equal losses in ecological diversity (Edie et al 2018), supporting the notion that these processes can be decoupled. This is important, because ecological diversity may increase the robustness and resilience of ecosystems, even as species diversity declines. Ecological diversity is likely to be important for both the maintenance and recovery of biodiversity

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Conclusion