Shrinking, an evolutionary necessity

Small is strong

The origin of modern mammals can be traced back more than 200 million years to the age of dinosaurs. But while dinosaurs evolved to become some of the largest land animals, for the following 150 million years, the ancestors of all modern mammals pursued an entirely different strategy: getting very small.

Modern mammals are unique in having a lower jaw consisting of just a single bone that bears teeth. In the course of evolution, fossils show that the lower jaw of mammalian ancestors became simplified and a new jaw joint was formed, while some of the other bones moved into the middle ear to aid in hearing.

An international team of scientists focused on the long-standing question of how it was possible to simplify and restructure the lower jaw, while still being able feed and hear, according to the study in Nature. Using X-ray computed tomography (CT) scanning of several fossil skulls and lower jaws, researchers generated digital models which were subjected to different computer simulations.

Their results showed that the small size of the fossil mammals significantly reduced the stresses in the jaw bones when feeding, while still being powerful enough to capture and bite through prey, such as insects.

Professor Emily Rayfield from the University of Bristol who led the study added: “The evolution of the mammalian jaw joint has perplexed palaeontologists for over 50 years. Using computational methods we can offer explanations to how our mammalian ancestors were able to maintain a working jaw while co-opting bones into a complex sound detection system.”

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Shrinking, an evolutionary necessity

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