Two major ecological shifts shaped 60 million years of ungulate faunal evolution

Abstract

The fossil record provides direct evidence for the behavior of biological systems over millions of years, offering a vital source for studying how ecosystems evolved and responded to major environmental changes. Using network analysis on a dataset of over 3000 fossil species spanning the past 60 Myr, we find that ungulate continental assemblages exhibit prolonged ecological stability interrupted by irreversible reorganizations associated with abiotic events. During the early Cenozoic, continental assemblages are dominated by mid-sized browsers with low-crowned teeth, which show increasing functional diversity. Around 21 Ma, the formation of a land bridge between Eurasia and Africa triggers the first major global transition towards a new functional system featuring a prevalence of large browsers with mid- to high-crowned molars. Functional diversity continues to increase, peaking around 10 Ma. Shortly after, aridification and the spread of C4-dominated vegetation lead to a second tipping point towards a fauna characterized by grazers and browsers with high and low crowned teeth. A global decline in ungulate functional diversity begins 10 Ma ago and accelerates around 2.5 Ma, yet the functional structure of these faunas remains stable in the latest Cenozoic. Large mammal evolutionary history reflects two key transitions, aligning with major tectonic and climatic events.