Rapid evolution was the source of the success of ancient crocodiles

New research from the University of Bristol has found that crocodiles once thrived on land and in the oceans as a result of rapid evolution.

Modern crocodiles are predators living in rivers, lakes and wetlands, catching fish, reptiles, birds and mammals with their visible snouts and powerful jaws.

However, new research published today in the journal Proceedings of the Royal Society B, shows that ancient crocodiles were once much more varied due to their rapid evolution.

During the time of the dinosaurs, some crocodiles experienced dolphin-like adaptations to living in the oceans, and others lived on land as fast-paced plant eaters.

Researchers studied more than 200 skulls and jaws, including fossils from the entire 230-million-year history of crocodiles and their extinct relatives. They explored variation in shape to reveal the differences between species and analyzed the speed at which groups of crocodiles changed over time.

It turns out that some groups of extinct crocodiles, including the dolphin-like thalattosuchians and small terrestrial notosuchians, evolved very rapidly over several million years, and they underwent great changes in their skulls and jaws as they ‘they developed in niches now occupied by other animals. groups, especially mammals.

Research also shows that crocodiles, alligators and gharials, the only living crocodilians, are more conservative than these extinct fossil groups and have evolved steadily over the past 80 million years, but there is no evidence of it. ‘a slowdown in their evolution and they are not “living fossils” as was once thought.

Lead author Dr Tom Stubbs, senior researcher at the School of Earth Sciences at the University of Bristol, said: “Crocodiles and their ancestors are an amazing group to understand the rise and fall of the earth. biodiversity.

“There are only 26 species of crocodiles today, most of which look very similar. However, there are hundreds of fossil species with dramatic variation, especially in their feeding apparatus.”

Dr Armin Elsler, Bristol School of Earth Sciences research associate and co-author, added: “New cutting-edge methods now allow us to test for differences in rate of change over time and between groups. “

It has long been suggested that dramatic changes in habitat and diet can trigger rapid evolution, but these patterns are generally only reported in groups of great variety today, such as birds, mammals and the fish. This is the first time this trend has manifested itself in crocodiles, a group with a rich fossil history, but low modern diversity.

Dr Stephanie Pierce, associate professor of organism and evolutionary biology at Harvard University, said: “Ancient crocodiles came in a dizzying array of shapes. They were suitable for running on land, swimming in water, catching fish, and even chewing plants.

“Our study shows that these very different lifestyles evolved incredibly quickly, allowing extinct crocodiles to thrive quickly and dominate new ecological niches over millions of years.”

Professor Michael Benton of Bristol added: “It is not clear why modern crocodiles are so limited in their adaptations. If we only had living species we could say that they are limited in their lifestyles by being in cold blood or because of their anatomy.

“However, the fossil record shows their amazing abilities, including a large number of species in the oceans and on land. Perhaps they only did well when the world’s climates were warmer than they are today. . ”