Early Cenozoic mammal radiation coincides with increased terrestrial habitability

Environmental variables like temperature, land availability and food availability constrain the ecological niches of terrestrial animals and, along with atmospheric oxygen levels, likely had a direct effect on their evolution and distribution over geological time. In this study we develop an agent-based terrestrial palaeoecological model, which we couple to an Earth system model to reconstruct how Earth’s habitability for terrestrial mammals has changed over the Mesozoic to Cenozoic eras. This allows us to investigate whether there was an environmental component to the early Cenozoic mammal radiation. Our findings indicate that Earth’s habitability for terrestrial mammals was maximised during the Cretaceous–Paleogene interval, due to the combination of elevated plant Net Primary Productivity (NPP), expansion of continental land areas, minimal glaciation, and elevated atmospheric oxygen levels. We propose that the rapid diversification of mammals during this period, while clearly enabled by the extinction of non-avian dinosaurs, was also influenced by the enhanced habitability of Earth’s surface during this time. Similar environmentally-driven changes in terrestrial habitability likely also play a significant role for other palaeobiological events.