New research from scientists at the University of Bristol explains how a ‘stop-start’ model of evolution, driven by environmental change, might explain why crocodiles have changed so little since the age of dinosaurs.
Today’s crocodiles look a lot like those from the Jurassic Period around 200 million years ago. There are also very few living species today – only 25. Other animals such as lizards and birds have reached a diversity of several thousand species in the same time span or less.
Prehistoric times also saw types of crocodiles that we don’t see today, including giants as large as dinosaurs, plant eaters, fast runners, and serpentine forms that lived in the sea.
In new research, published today in the journal Communication biology of nature, scientists explain how crocodiles follow a pattern of evolution called “punctuated equilibrium”.
The pace of their evolution is usually slow, but sometimes they evolve faster because the environment has changed. In particular, this new research suggests that their evolution speeds up when the climate is warmer and their body size increases.
Lead author Dr Max Stockdale, School of Geographical Sciences, University of Bristol, said: “Our analysis used a machine learning algorithm to estimate the rates of change. is the amount of change that has taken place over a given period of time, which we can establish by comparing the measurements of the fossils and taking into account their age.
“For our study, we measured body size, which is important because it interacts with how fast animals grow, how much food they need, the size of their populations, and the likelihood of them going extinct. “
The results show that the limited diversity of crocodiles and their apparent lack of evolution is the result of a slow rate of evolution. It seems that crocodiles have come up with a very effective body plan that is versatile enough that they don’t need to change it to survive.
This versatility could explain why crocodiles survived the impact of meteors in the late Cretaceous Period, during which dinosaurs perished. Crocodiles generally thrive best in warm conditions because they cannot control their body temperature and need the warmth of the environment.
The climate during the time of the dinosaurs was warmer than it is today, and that may explain why there were many more varieties of crocodiles than we see now. Being able to draw energy from the sun means that they don’t need to eat as much as a warm-blooded animal like a bird or mammal.
Dr Stockdale added: “It is fascinating how complex a relationship between the earth and the living things we share it with. Crocodiles have landed on a lifestyle versatile enough to adapt to the huge changes. environmental issues since dinosaurs were there. “
The next step in the team’s research is to find out why some types of prehistoric crocodiles went extinct, while others were not.
Ancient African skull sheds light on the origins of the American crocodile
“Environmental factors in the evolution of body size in archosaurs of the crocodile lineage” Dr Maximilian T. Stockdale and Professor Michael J. Benton, Nature Communications Biology, 2021.
Provided by the University of Bristol
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