Tiny Fossils Reveal How Shrinking Was Essential for Successful Evolution

A new study published today in Nature shows that getting smaller was a key factor contributing to the exceptional evolution of mammals over the last 200 million years.

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.

An international team of scientists from the United Kingdom and the US have used modern computer analysis to take a look at what happened to the skeleton of our tiny mammal ancestors.

Modern mammals are unique in having a lower jaw consisting of just a single bone that bears teeth. In contrast, all other vertebrates possess complex lower jaws formed by at least five or more bones joined together. 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.

The team’s research focussed on the long-standing question of how it was possible to simplify and restructure the lower jaw, while still being able feed and hear. Using X-ray computed tomography (CT) scanning of several fossil skulls and lower jaws, the researchers generated digital models which were subjected to different computer simulations.

Life reconstruction of the mammaliaform Morganucodon found in Jurassic sediments of Wales and China. Morganucodon was one of the smallest fossil mammal ancestors with a size of 4-6cm