New research at the University of Bristol by scientists describes how a “stop-start” evolution pattern dictated by environmental change might explain why crocodiles have changed so little since the dinosaur period.
Today’s crocodiles look very close to those of some 200 million years ago in the Jurassic period.
Also, very few animals are alive today – just 25. In the same time span, other animals, such as lizards and birds, reached a diversity of several thousands of species or fewer.
There have also been crocodile species in prehistory that we do not see today, including giants as big as dinosaurs, herbivores, swift runners, and snake-like forms that lived in the sea.
Scientists explain in the new report, published today in the journal Nature Communications Biology, how crocodiles adopt an evolutionary trend known as’ punctuated equilibrium.’
In general, the pace of their evolution is slow, but because of environmental changes, they often evolve faster.
The new research indicates that their development speeds up, especially when the environment is warmer and their body size increases.
“Lead author Dr. Max Stockdale of the School of Geographical Sciences at the University of Bristol said, “Our study used a machine learning algorithm to estimate evolution rates.
The rate of evolution is the amount of change that has happened in a given period of time. By comparing measurements from fossils, we can quantify it, taking into account how old they are.
“For our study, we measured body size, which is important because it’s related to how fast animals grow, how much food they need, how large their populations are and how likely they are to go extinct.”
The findings suggest that the limited diversity and obvious lack of evolution of the crocodiles is a consequence of a slow rate of evolution.
Crocodiles seem to have arrived at a body plan that was very powerful and flexible enough that they did not need to modify it in order to survive.
This versatility may help explain why, at the end of the Cretaceous period that killed the dinosaurs, crocodiles survived the meteorite impact.
In warm environments, crocodiles usually survive best because they can not regulate their body temperature and require heat from the atmosphere.
During the dinosaur period, the atmosphere was colder than it is today, and this may explain why there were far more crocodile species than we see today.
They may not have to feed as much as warm-blooded animals, including birds or rodents, because they are able to draw nutrition from the sun.
“It’s fascinating to see how complicated the relationship between the Earth and the creatures with whom we share it is,” Dr. Stockdale added.
Crocodilians have adopted a lifestyle that is sufficiently adaptive to respond to the tremendous changes in the climate that have occurred since dinosaurs lived.
The next step in the team’s research is to figure out why certain ancient crocodile species have become extinct, while others have not.
Reference, by Dr. Maximilian T. Stockdale and Professor Michael J., “Environmental Drivers of Body Size Evolution in Crocodile-Line Archosaurs,”
Benton, January 7, 2021. Biology of Nature Communications.