Contrary to popular belief, the rise of land mammals may not be solely linked to the disappearance of dinosaurs. A study reveals that their transition had begun much earlier, under the influence of major vegetation changes.
This discovery challenges the traditional narrative that the asteroid impact 66 million years ago freed mammals from dinosaur domination. The analysis of bone fragments shows that their adaptation to terrestrial life was already underway, driven by the expansion of flowering plants.
A transition initiated before the catastrophe
Researchers from the University of Bristol studied limb bones of therian mammals, ancestors of modern marsupials and placentals. These fragments, from western North America, reveal adaptations for terrestrial locomotion several million years before the Cretaceous extinction.
Palaeontology published these findings, obtained by comparing fossil bone structures with those of modern species. Flowering plants, by diversifying ground habitats, likely facilitated this transition. Meanwhile, arboreal mammals were already in decline before the asteroid impact.
This innovative method uses tiny fragments, whereas previous studies required complete skeletons. The data come from museum collections in New York, Calgary, and California, offering an unprecedented glimpse into the evolution of an entire community.
A change driven by vegetation, not dinosaurs
The study dismisses the idea that dinosaurs hindered mammal evolution. Their small size during the Mesozoic is better explained by the limited ecosystems of the time. The emergence of angiosperms created ecological niches favorable to diverse terrestrial life.
Multituberculates, widespread primitive mammals of the era, were not included in the analysis. Their bones, too different, did not allow for the same conclusions. Researchers emphasize that plant habitats played a far more decisive role than the presence of dinosaurs.
This work sheds light on a gradual adaptation, independent of the later catastrophe. It suggests mammals would have continued colonizing Earth even without dinosaur extinction, given how their environment was transforming.
Article author: Cédric DEPOND