A lot has changed since the age of dinosaurs hundreds of millions of years ago. Humans didn't exist and dinosaurs are gone. Yet crocodiles are still here and, unlike humans, have not evolved much by comparison.
They even look similar to ones from the Jurassic period some 200 million years ago.
A new study find that it's due to a 'stop-start' pattern of evolution, governed by environmental change. This pattern of evolution known as "punctuated equilibrium" is generally slow, but occasionally means faster evolution because the environment has changed. This new research suggests that their evolution speeds up when the climate is warmer, and that their body size increases.