They say, punctuated equilibrium (punk eek):
In the new research, published today in the journal Nature Communications Biology, the scientists explain how crocodiles follow a pattern of evolution known as ‘punctuated equilibrium’.
The rate of their evolution is generally slow, but occasionally they evolve more quickly because the environment has changed. In particular, this new research suggests that their evolution speeds up when the climate is warmer, and that their body size increases.
Lead author Dr Max Stockdale from the University of Bristol’s School of Geographical Sciences, said: “Our analysis used a machine learning algorithm to estimate rates of evolution. Evolutionary rate is the amount of change that has taken place over a given amount of time, which we can work out by comparing measurements from fossils and taking into account how old they are.
“For our study we measured body size, which is important because it interacts with how fast animals grow, how much food they need, how big their populations are and how likely they are to become extinct.”
The findings show that the limited diversity of crocodiles and their apparent lack of evolution is a result of a slow evolutionary rate. It seems the crocodiles arrived at a body plan that was very efficient and versatile enough that they didn’t need to change it in order to survive.
This versatility could be one explanation why crocodiles survived the meteor impact at the end of the Cretaceous period, in which the dinosaurs perished. Crocodiles generally thrive better in warm conditions because they cannot control their body temperature and require warmth from the environment.University of Bristol, “Why crocodiles have changed so little since the age of the dinosaurs” at ScienceDaily
The paper is open access.
One way of looking at it: After you are a crocodile, there is no place for you to go.