Down to earth: therian mammals became more terrestrial towards the end of the Cretaceous

The end Cretaceous extinctions had a profound effect on mammalian diversity, especially on metatherians (marsupials and their extinct relatives). Could mammalian substrate preference have influenced differential survival patterns? The plant fossil record shows changing angiosperm leaf anatomy during the last ten million years of the Cretaceous that would have resulted in a greater richness of terrestrial understory habitats, and work by other researchers implies that terrestrial (vs arboreal) substrate preference promoted increased survival over the Cretaceous–Palaeogene boundary for both mammals and birds. Here we use fragmentary postcranial remains of Late Cretaceous mammals and show that, at least in the Western Interior of North America, therian mammals were becoming more terrestrial in their locomotor mode towards the end of the Cretaceous.