The number of bones in mammalian skulls has dwindled over time, a change that appears to have supported more efficient feeding. This finding comes from research conducted with input from the University of Birmingham and collaborators.
In many vertebrate groups, including fish and reptiles, the skull is made up of numerous small bones that fuse as evolution proceeds. A similar, highly segmented skull architecture existed in the earliest mammals, which emerged roughly 300 million years ago. Over the next 150 to 100 million years, the count of skull bones gradually declined as the lineage evolved.
For years, scientists thought the reduction in skull bones primarily strengthened the bite or reinforced skull integrity. New investigations show a different mechanism. Stefan Lautenschlager and his colleagues describe a shift in how mechanical stress is distributed during feeding, with bones being moved away from the brain region toward the sides of the skull. This redistribution may have allowed for a larger brain over generations.
According to the researchers, the drop in bone numbers altered skull mechanics during feeding, causing a divergence of strain away from the braincase toward the lateral skull walls. This reorganization could contribute to brain enlargement as mammals adapted to new dietary demands.
As skull bones became fewer, mammals also tended to reach smaller body sizes, with some individuals measuring only about 10 to 12 millimeters in length at certain stages. This miniaturization constrained the range of foods available, steering ancestral mammals toward insect consumption as a viable feeding strategy.
That combination of small size, reduced skull bones, and new insect prey helped the ancestors of modern mammals survive during the dinosaur era and later thrive after dinosaurs disappeared. The post-dinosaur era opened ecological opportunities, allowing many mammal lineages to expand their niches and grow to sizes well beyond most dinosaurs in some ecosystems.
Glimpses from ancient biology hint at additional adaptive strategies, including how certain tiny insects may have influenced predator-prey dynamics in the prehistoric world. These insights underscore how shifts in skull architecture and body size can align with broad ecological opportunities, shaping the course of mammalian evolution. (Attribution: University of Birmingham study)