Tseng, Z. J.; Li, Q.; Ting, S.

The first 10 million years (Myr) following the Cretaceous-Paleogene (K-Pg) mass extinction marked a period of global greenhouse conditions and dramatic rise of placental mammals. Because ~80% of known terrestrial sections capturing post-K-Pg mammal recovery come from North America, a substantial knowledge gap exists in the tempo and mode of recovery in Asia, where only 3% of sites are located and most contain species found nowhere else. We show that isolated Paleocene placental assemblages from China (1) reached high tooth size disparity early in the Paleocene, (2) tracked regional and global environmental changes in their dental shape later in the Paleocene, and (3) achieved maximum dental shape-performance integration near the end of the first 10 Myr post-K-Pg. This brawn before bite transformation, coupled with prolonged dental shape versus performance variability, favors a scenario whereby many living orders of placental mammals were borne out of phenotypically and functionally plastic ancestral assemblages, including those in tropical south China, during the Paleocene.