Brawn before bite in endemic Asian eutherian mammals after the end-Cretaceous extinction.

内容摘要

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 global sites are located and most contain species found nowhere else. We show that isolated Paleocene eutherian assemblages from China (1) exhibited high mean tooth size and disparity early in the Paleocene, (2) shifted in their dental shape in parallel with regional and global environmental changes later in the Paleocene, and (3) achieved maximum dental shape-performance covariation 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 eutherian mammals were borne out of phenotypically and functionally plastic ancestral assemblages, including those in tropical South China, during the Paleocene. Over the course of Earth's history, five major mass extinctions have shaped life as we know it today. The most recent occurred around 66 million years ago at the end of the Cretaceous Period, leading to the demise of non-avian dinosaurs and ushering in the age of mammals. Most of what we know about how mammals recovered from this mass extinction comes from fossil sites in North America. Far less is known about how ancient mammals in other parts of the world adapted to a dramatically altered environment after the disappearance of large dinosaurs. Tseng, Li and Ting investigated how some of the earliest mammal species in Asia recovered following this global mass extinction. They studied 200 individual teeth from 48 specimens of extinct mammals, including members of the Pantodonta (large herbivorous mammals), Arctostylopidae (stocky herbivorous and omnivorous mammals), and Anagaloidea (a group closely related to rodents). Using high-resolution 3D models of these rare fossil teeth, the researchers quantified variation in tooth shape and function. Their analyses revealed that mammals in East Asia, particularly South China, were already relatively large during the early Palaeocene, the first epoch of the age of mammals. Over the next five million years, their teeth became increasingly specialised for different forms of chewing and food processing, reflecting the likely diversification of diets and ecological niches within mammal communities. The findings also suggest that these early mammals were ecologically flexible, meaning they were able to exploit a wide range of food resources and adapt to changing environmental conditions. As ecosystems recovered and transformed during the first 10 million years after the end-Cretaceous mass extinction, the relationship between tooth shape and function also shifted, indicating changing evolutionary pressures and ecological opportunities. The study by Tseng, Li and Ting helps fill an important gap in our understanding of how biodiversity recovered in different regions of the world following the most recent major mass extinction. Their findings may also inform predictive models and conservation strategies aimed at understanding how modern animals could respond to future biodiversity crises. Insights from the past can help us prepare for the present and future, as rapid climate and environmental change increasingly challenge the coexistence of humans and the natural world.