A revelatory cache of fossils dug up in central Colorado details as never before the rise of mammals from the post-apocalyptic landscape after an asteroid smacked Earth 66 million years ago and annihilated three-quarters of all species, including the dinosaurs.

The fossils, described by scientists on Thursday, date from the first million years after the calamity and show that the surviving terrestrial mammalian and plant lineages rebounded with aplomb. Mammals, after 150 million years of subservience, attained dominance. Plant life diversified impressively.

With dinosaurs no longer eating them, mammals made quick evolutionary strides, assuming new forms and lifestyles and taking over ecological niches vacated by extinct competitors. Within 700,000 years their body mass had become 100 times bigger.