A new study unveils that beginning with small and basic factors was crucial for the development of mammals.

April 12, 2023

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by University of Birmingham

The ancestors of modern mammals were able to evolve into one of the most successful animal lineages by starting out small and simple, according to a new study. The study, published in Communications Biology by an international team of paleontologists, demonstrates that reducing the number of skull bones in early mammals around 150 to 100 million years ago did not lead to higher bite forces or increased skull strength, as hypothesized for many decades. Instead, the team found that the skull shape of these early mammals redirected stresses during feeding in a more efficient way.

The researchers used computer simulations and stress analyses to investigate the purpose of this skull simplification. They discovered that reducing the number of skull bones led to a redistribution of stresses in the skull of early mammals, allowing for stress to be redirected from the part of the skull housing the brain to the margins of the skull during feeding. This may have allowed for an increase in brain size, paving the way for the diversification of mammals that led to the development of the wide range of creatures we see today.

Lead author Dr. Stephan Lautenschlager, Senior Lecturer for Palaeobiology at the University of Birmingham, said, "Changes to skull structure combined with mammals becoming smaller are linked with a dietary switch to consuming insects—allowing the subsequent diversification of mammals which led to development of the wide-range of creatures that we see around us today."

The study also found that alongside the reduction of skull bones, early mammals also became a lot smaller, with some having a skull length of only 10–12 mm. This miniaturization considerably restricted the available food sources, and early mammals adapted to feeding mostly on insects. This combination of small size, reduced number of skull bones, and feeding on new food sources allowed the ancestors of modern mammals to thrive in the shadows of the dinosaurs.

However, it was not until dinosaurs became extinct at the end of the Cretaceous, some 66 million years ago, that mammals had a chance to further diversify and reach the large range of body sizes we see today.

Journal information: Communications Biology

Provided by University of Birmingham