The Cretaceous-Paleogene boundary marks a critical event in mammalian evolution. Using a database of 4769 mammalian specimens from the Hell Creek and lower Fort Union formations of Garfield County, northeastern Montana, I quantified temporal patterns of diversity and community structure to evaluate faunal dynamics during the last ~1.9 m.y. of the Cretaceous, the Cretaceous-Paleogene extinction and survival, and the first ~1.2 m.y. of the early Paleocene recovery and placental radiation.

Mammalian taxonomic composition and species richness remained relatively stable for most of the last ~1.9 m.y. of the Cretaceous, but the relative abundance of metatherians and evenness of paleocommunities began...